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DEPARTMENT   OF  THE    INTERIOR 


MONOGRAPHS 


OF  THE 


United  States  Geological  Survey 


VOLUME    XXXII 
F^RT   II 


WASHINGTON 

GOVERNMENT    PRINTING    OFFICE 

1899 


UNITED  STATES  GEOLOGICAL  SURVEY 

CHARLKS  II.  WALCOTT,  DIRKCTOK 


GEOLOGY 


YELLOWSTONE   NATIONAL  PARK 


P^RT    II 

DESCRIPTIVE  GEOLOGY,  PETROGRAPHY,  AND  PALEONTOLOGY 


ARNOLD  HAGUE,  J.  P.  IDDINGS,  W.  H.  WEED 


C.  D.  WALCOTT,  G.  H.  6IRTY,  T.  W.  STANTON,  AND  F.  H.  KNOWLTON 


V. 


WASHINGTON 

GOVERNMENT    PRINTING    OFFICE 
1899 


^510 


CONTENTS, 


Page. 

Letter  of  transmittal xiii 

OUTLINK XV 

Chapter  I. — Descriptive  geology  of  the  Gallatin  Mountains,  by  J.  P.  IcUlings  and  W.  H. 

Weed 1 

Introduction 1 

The  Crags  and  vicinity 3 

The  Crags 3 

Crowfoot  section 6 

Mountains  south  of  Panther  Creek 9 

South  End  Hills 10 

Trilobite  Point 11 

The  Dome 12 

Indian  Creek  laccolith 13 

Mount  Holmes  by sraallth 16 

Antler  Peak 20 

Three  River  Peak 23 

Bighorn  Pass 24 

Crowfoot  Ridge  and  Gallatin  Valley 27 

Quadrant  Mountain,  Bannock  Peak,  and  the  valley  of  the  Gallatin  Eiver 31 

Banuock  Peak 31 

Quadrant  Mountain 33 

Little  Quadrant  Mountain  and  Fawn  Creek  Valley 36 

Little  Quadrant  Mountain 36 

Fawn  Creek  Valley 39 

Region  north  of  Gallatin  River 41 

The  Fan 45 

Electric  Peak 50 

Western  flanks  of  the  Gallatin  Range 56 

Eastern  flank  of  the  Madison  Range 57 

Chapter  II. — The  intrlsive  rocks  of  the  Gallatin  Mountains,  Bunsen  Peak,  and  Mount 

Everts,  by  J.  P.  Iddings 60 

Indian  Creek  laccolith 60 

Hornblende-mica-andesite-porphy  ry 60 

Mount  Holmes  bysmalith 64 

Dacite-porphyry , 64 

Bighorn  Pass  sheet 69 

Kersantite 69 

Gray  Mountain  mass  and  connected  sheets 73 

Hornblende-mica-andesito  porphyry  and  andesite 73 

Hornbleude-andesite-porphy ry  and  andesite 77 

Hornblende-pyroxene-andesite-porphyries  and  andesites 80 

Chemical  composition 81 

V 


VI  CONTENTS. 

Chapter  II — Continued.  Page. 

Ditterentiated  sheet  southeast  of  Electric  Peak 82 

Gallatin  River  laccolith 84 

Dacite-porphy  ry 84 

Intrusive  sheets  in  Mount  Everts 85 

The  Bunsen  Peak  mass 86 

Daeite-porphy  ry 86 

Chapter  III. — The  igneous  rocks  of  Electric  Peak  and  Sepulchre  Mountain,  hy  J.  P. 

Iddings 89 

Geological  sketch  of  the  region 89 

The  intrusive  rocks  in  Electric  Peak 92 

The  dike  rock.s  and  certain  contact  forms  of  the  stock 94 

The  stock  rocks  and  apophyses 97 

Varieties  in  which  the  dark-colored  and  light-colored  minerals  are  nearly  equal 99 

Varieties  in  which  the  light-colored  minerals  are  in  excess,  hut  in  which  quartz  is 

not  excessive 102 

Varieties  with  an  excess  of  light-colored  minerals,  in  which  quartz  is  abundant 103 

Quartz-mica-diorite-porphyry 103 

General  consideration  of  the  mineral  and  chemical  composition  of  the  intrusive  rocks 

in  Electric  Peak 105 

Mineral  composition 105 

Chemical  composition 115 

The  volcanic  rocks  of  Sepulchre  Mountain 121 

The  lower  breccia 121 

The  upper  breccia 122 

The  dike  rooks 128 

General  consideration  of  the  mineral  and  chemical  composition  of  the  eruptive  rocks 

of  Sepulchre  Mountain 134 

Miueral  composition 134 

Chemical  composition 135 

The  extrusive  igneous  rocks  west  and  southwest  of  the  Gallatin  Mountains 137 

Comparison  of  the  rocks  from  Electric  Peak  and  Sepulchre  Mountain 138 

Correlation  of  the  rocks  on  a  chemical  basis 142 

Chapter  IV. — Descriptive  geology  op  the  northern  end  of  the  Teton  Range,  by  J.  P. 

Iddings  and  W.  H.  Weed 149 

Introduction 149 

Topographic  features 151 

Crystalline  axis  aud  region  east 152 

Region  west  of  the  crystalline  axis 157 

Chapter  V. — Descriptive  geology  of  Huckleberry  Mountain  and  Big  Game  Ridge,  by 

Arnold  Hague 165 

General  features 165 

Region  of  Wildcat  Peak  and  Huckleberry  Mountain 168 

Region  of  Snake  River  gorge 173 

Region  between  Red  and  Basin  creeks 175 

Snake  River  Hot  Springs 177 

Region  of  Coulter  Creek  and  Bobcat  Ridge 179 

Region  of  Wolverine  Creek 181 

Region  of  Pinyon  Peak 184 

Big  Game  Ridge '. 188 

Chicken  Ridge 191 


CONTENTS.  VII 

ClUPTF.n  V — Continued.  Page. 

Outlet  t'iiiiyoii 194 

Clianui'l  Miiuntaiii 196 

Flat  Mouutaiii 196 

West  Base  of  Two  Ocean  Plateau 197 

Two  Ocean  Plateau 200 

ChaI'TKR  VI.— (JkoI.OGY  of  the  80UTHEHN  END  OF  THE  Snowy  Range,  by  W.  H.  Weed 203 

(ieueial  description 203 

Topography 201 

Sedimentary  rocks 20.5 

Buffalo  Plateau 206 

Lamar  Valley 207 

Slough  Creek 208 

Soda  Butte  Creek 210 

Pebble  Creek 211 

Soda  Butte  Valley 212 

CiiArxER  VII.— The  dissected  volcano  of  Crandall  Basin,  Wyoming,  by  J.  P.  Iddings..  21,5 

Introduction 215 

Geological  description 216 

General  features 216 

Early  acid  breccia 219 

Basic  breccia  and  flows 220 

Distinctly  bedded  breccia 221 

Chaotic  breccia 222 

Dikes 224 

Extent  of  erosion 232 

Petrography  of  the  rocks  of  the  district 237 

Early  acid  breccia 237 

Basic  breccia  and  lava  flows 238 

Basalt  flows 239 

Intrusive  rocks 240 

Outlyiug  dikes 240 

Granular  core  and  intersecting  dikes 246 

Mineral  and  chemical  variations  of  rocks 259 

Crystallization 265 

Development  of  pheuocrysts 266 

Chapter  VIII. — The  igneous  rocks  of  the  Absaroka  Range  and  Two  Ocean  Plateau 

and  op  outlying  portions  of  the  Yellowstone  National  Park,  by  J.  P.  Iddings 269 

Introduction 269 

Early  acid  breccia 270 

Early  basic  breccia  and  associated  basaltic  flows 275 

Late  acid  breccia 281 

Late  basic  breccia 296 

Dikes  and  surficial  flows 304 

Vicinity  of  Sylvan  Pass 304 

Dikes  south  and  southeast  of  Sylvan  Pass 311 

Massive  flows  and  intrusions  of  light-colored  andesite 314 

Trachy tic  rhyolite 321 

Chapter  IX. — Absarokitk-shoshonite-banakite  series,  by  J.  P.  Iddings 326 

Introduction 326 

Absarokite 328 


VIII  CONTENTS. 

Chapter  IX— Continued.  Page. 

Shoahonite 339 

Banakite 347 

Similar  rocks  in  Montana 351 

Chapter  X.— The  khyoi.ites,  Ijy  J.  P.  Iddings 356 

Introduction 356 

Megascopical  cliaracters 357 

Vicinity  of  the  Mammotli  Hot  Springs 357 

Obsidian  Cliff 359 

Canyons  of  Gibbon  River  and  Madison  River 366 

Madison  Plateau  north  of  the  Lower  Geyser  Basin 367 

Vicinity  of  the  Lovrer  Geyser  Basin 369 

Upper  Geyser  Basin 372 

Madison  Plateau  south  of  the  Geyser  basins 374 

Bechler  Canyon 375 

Falls  River  Basin 377 

Pitchstone  Plateau 379 

Red  Mountains 381 

Vicinity  of  Yellowstone  Lake 382 

Natural  Bridge 386 

North  and  east  of  Yello wstoue  Lake 387 

Vicinity  of  Yellowstone  River 388 

Vicinity  of  the  Grand  Cauyon  of  the  Yellowstone 389 

Northeastern  corner  of  Yellowstone  Park 391 

Microscopical  characters  of  the  rhyolite 393 

Phenocrysts 394 

Quartz 395 

Sanidiue 398 

Plagioclase 399 

Pyroxene 399 

Magnetite  and  titaniferous  iron  oxide 400 

Zircon ^01 

Pseudobrookite *01 

AUanite  and  apatite 402 

Groundmass 4"2 

Glasses  free  or  almost  free  from  microlites 403 

Globulitic  glass 406 

Microlitic  glass 408 

Forms  of  growth  of  microscopic  crystals 410 

Lithophysie ^^° 

Microgr.anular  structure - 4— 

Relations  of  the  various  microstructures  to  one  another  in  the  rock  mass 423 

Lamination  and  banding 41.4 

Variations  in  composition  among  the  rhyolites 427 

Intermingled  rhyolite  and  basalt 430 

Chapter  XL— Recent  basalts,  by  J.  P.  Iddings 433 

Ophitic  basalt "136 

Basalts  related  to  those  with  ophitic  structure 437 

A'ery  fiue-grained  bas.alts  with  minute  phenocryts - 439 

Chapter  XIL— Paleozoic  fossils 440 

Section  I.— Cambrian  fossils,  by  C.  D.  VValcott 440 

Section  II.— Devonian  and  Carboniferous  fossils,  by  G.  H.  Girty 479 


CONTENTS.  IX 

Pago. 

Chaptku  XIII. — Mksozoic  Fds.siLS,  by  T.  W.  Stanton 600 

Chai'Ter  XIV. — Fossil,  I'l.oitA,  by  F.  H.  Knowlton ''51 

Historical  sunimary *'51 

Enumeration  anil  description  of  fossil  plants  from  the  Laramie 6.^5 

Discussion  of  Laramie  flora ''"3 

Enumeration  and  duscription  of  fossil  plants  from  the  Tertiary 665 

Plants,  exclusive  of  fossil  wood ''65 

Fossil  forests .- ^^5 

Biological  consideration  of  the  Tertiary  flora 773 

Geological  consideration  of  the  Tertiary  flora 783 

Indkx *^83 


ILLUSTRATIONS. 


Page. 

Plate                I.  Mountains  north  of  Mount  Holmes 4 

II.  Paleozoic  section,  Crowfoot  Ridge 8 

III.  Geological  cross  sections  of  Gallatin  Range 12 

IV.  Panoramic  view  of  Gallatin  Range  from  Norris  Geyser  Basin 18 

V.  Cross  sections  showing  Mount  Holmes  bysmalith 18 

VI.  Antler  Peak  from  valley 22 

VII.  Three  River  Peak  from  Gallatin  Valley 24 

VIII.  Bannock  Peak  from  Panther  Creek  Valley 32 

IX .  Geological  cross  sections 50 

X.  Geological  map  of  Gallatin  Range 56 

XI.  Photomicrographs  of  audesiteporphyry  and.  dacite-porphyry 62 

XII.  View  of  Echo  Peak 68 

XIII.  Electric  Peiik  from  Sepulchre  Mountain 90 

XIV.  Head  of  East  Gulch  of  Electric  Peak 90 

XV.  Sepulchre  Mountain  from  its  northwest  spur 96 

XVI.  Geological  map  of  Electric  Peak  and  Sepulchre  Mountain 96 

XVII.  Diorites 100 

XVIII.  Granite  and  diorite-porphy ry 100 

XIX.  Photomicrographs  of  andesite-porphyry  and  diorite 104 

XX.  Photomicrographs  of  diorite  and  diorite-porphyry 104 

XXI.  Photomicrographs  of  diorite-porphyry  and  dacite 104 

XXII.  Photomicrographs  of  pyroxene-andesite  and  dacite 130 

XXIII.  Map  of  the  northern  end  of  the  Teton  Range 150 

XXIV.  Snake  River  Hot  Springs 178 

XXV.  Outlet  Canyon 194 

XXVI.  BarouettPeak 204 

XXVII.  Geological  map  showing  dissected  volcano  of  Crandall  Basin,  Wyoming 216 

XXVIII.  Index  Peak 218 

XXIX.  The  Thunderer  and  Mount  Norris 222 

XXX.  Koodoos 222 

XXXI.  Hurricane  Ridge 226 

XXXIl.  Geological  cross  sections 232 

XXXIII.  Photomicrographs  of  gabbro,  diorite,  and  granitic  aplite 250 

XXXIV.  Photomicrographs  of  monzouite,  diorite,  and  basalt 250 

XXXV.  Eagle  Peak 296 

XXXVI.  Photomicrographs  of  absarokite 332 

XXXVII.  Photomicrographs  of  shoshonite  and  diorite-porphyry 344 

XXXVIII.  Photomicrographs  of  banakite,  quartz-banakite,  and  andesite 350 

XXXIX.  Obsidian  Cliff  columns 360 

XL.  Top  of  columns 360 

XLI.  Lithophysie 364 

XI 


XII  ILLUSTRATIONS. 

Page. 

Plate        XLII.  Fissile  litboidal  rhyolite,  Obsidian  Cliff 364 

XLIII.   Lithophys:^ 364 

XLIV.  Columnar  rhyolite 364 

XLV.  Columnar  Cliff,  Madison  Canyon 368 

XLVI.  Banded  perlite 370 

XLVII.  Perlite  with  spherulites 370 

XLVIII.  Natural  Bridge 386 

XLIX.  Natural  Bridge,  vertical  plates 386 

L.  Photomicrographs  of  rhyolitiu  glasses 406 

LI.  Photomicrographs  of  rhyolitio  glasses 406 

LII.  Spherulites 410 

LIU,  Spherulites  and  feldspar  needles 414 

LIV.  Photomicrographs  of  micrographic  phenocrysts  and  spherulites 414 

LV.  Photomicrographs  of  spherulitic  structures 414 

LVI.  Photomicrographs  of  spherulitic  structures  and  feldspar  microlites 422 

LVII.  Diagrams  of  lithophys;e 422 

LVIII.  Columnar  structure 436 

LIX.  Photomicrographs  of  basalt '. 436 

LX-LXV.  Cambrian  fossils 468-478 

LXVI-LXXI.  Devonian  and  Carboniferous  fossils 580-598 

LXXII-LXXVI.  Mesozoic  fossils 642-650 

LXXVII-CXXI.  Fossil  flora 794-882 

Fig.  1.  Diagram  showing  variation  in  silica  percentages  of  rocks  from  Electric  Peak 117 

2.  Diagram  showing  molecular  variation  of  the  rocks  at  Electric  Peak 119 

3.  Diagram  showing  molecular  variation  of  the  rocks  of  Sepulchre  Mountain 136 

4.  Sections  of  spherulites  with  projecting  prisms  of  orthoclase  and  a  crescent-shaped  belt 

free  from  granulation  413 


LETTER  OF  TRANSMITTAL, 


Department  of  the  Interior, 

United  States  Geological  Survey, 

Washington,  D.  C,  June  30,  1896. 
Sir:  1  have  the  honor  to  transmit  herewith  the  manuscript  of  Part  II 
of  a  monograph  on  the  Geology  of  the  Yellowstone  National  Park.  It 
embraces  chapters  on  the  descriptive  geology  of  the  mountains  surrounding 
the  Park  Plateau,  by  myself  and  colleagues;  elaborate  investigations  of 
the  petrography  of  the  crystalline  rocks,  by  Prof.  J.  P.  Iddings;  reports 
upon  the  invertebrate  paleontology  of  the  Park  and  the  Absaroka  Range, 
by  Messrs.  C.  D.  Walcott,  George  H.  Girty,  and  T.  W.  Stanton;  and  an 
exhaustive  study  of  the  fossil  flora  of  the  region,  by  Mr.  F.  H.  Knowlton 
Very  respectfully, 

Arnold  Hagie, 

Geologist  in  Charge. 
Hon.  Charles  D.  Walcott, 

Director  United  States  Geological  Survey. 

XIII 


OUTLINM:  OF  THIS  VOLUME. 

CiiArTEK  I.  The  (iallatin  Mountains,  extending  IK  miles  within  the  boundary  of  the  Yellowstone 
National  Talk,  consist  of  sedimentary  strata  ranging  from  the  Cambrian,  through  the  Silurian, 
Devonian,  Carboniferous,  and  Juratrias,  to  the  Laramie  of  the  Cretaceous.  These  sedimentary  rocks 
have  been  uplifted  by  forces  acting  from  the  southwest.  They  dip  northeast,  and  have  been  folded 
to  a  slight  extent  transverse  to  the  strike.  .Subseqnently  they  have  been  strongly  faulted.  The  dis- 
location at  the  close  of  the  Laramie  was  accompanied  by  intrusions  of  igneous  magmas  in  several 
large  lacoolithio  bodies  and  in  numerous  sheets,  and  in  the  vicinity  of  Electric  Peak  by  dikes.  Erosion 
has  uncovered  crystalline  schists  at  the  southern  and  southwestern  end  of  the  range,  and  has  laid  baie 
exposures  of  all  the  sedimentary  and  igneons  rocks.  Finally,  glaciation  has  modified  the  topography 
in  a  striking  manner.  The  structural  relations  of  the  sedimentary  and  igneous  rocks  are  illustrated 
by  a  number  of  geological  sections. 

Chapter  II.  Thi.s  chapter  treats  almost  exclusively  of  the  intrusive  rocks  of  the  Gallatin  Moun- 
tains. They  are  mainly  line-grained  and  aphanitic  masses,  in  most  occurrences  porphyritic  and 
andesitic  in  character.  The  large  bodies  differ  from  one  another  .somewhat  in  composition,  and  vary 
slightly  in  texture,  in  diH'erent  parts  of  the  rock  bodies.  In  one  intrusive  sheet  there  has  been  a  pro- 
nounced dlft'erentiation  by  the  settling  of  phenocrysts  of  augite. 

Chapter  III.  Electric  Peak  aud  Sepulchre  Mountain  are  described  as  parts  of  a  Tertiary  volcano 
■which  were  faulted  across  the  conduit,  the  amount  of  vertical  displacement  having  been  more  than 
5,000  feet.  The  deeper  i)ortion.s  of  the  mountains,  consisting  of  sedimentary  strata  intersected  by 
dikes,  sheets,  and  the  stock  or  conduit  of  the  volcano,  have  been  brought  to  the  surface,  as  shown  in 
the  mass  of  Electric  Peak.  The  ejected  breccias  and  lava  flows,  together  with  the  upper  portion  of 
the  conduit,  constitute  Sepulchre  Mountain.  Lavas  which  are  andesites  in  the  latter  mass  are  diorites 
and  porphyries  in  the  former.  Rocks  with  like  chemical  composition  are  found  to  have  different 
mineral  composition  according  as  they  are  crystallized  into  phanerocrystalline  diorites  or  into  apha- 
nitic andesites. 

Chapter  IV.  The  northern  end  of  the  Teton  Range  extends  but  a  short  distance  within  the  Yellow- 
stone National  Park.  It  consists  of  a  nucleus  of  crystalline  schists  aud  gneisses  overlain  by  Paleozoic 
and  Mesozoie  strata  flexed  in  an  anticline  witli  northward-dipping  axis  and  faulted  to  a  slight  extent. 
Birch  Hills,  a  few  miles  to  the  north,  are  an  outlier  of  the  range.  Upon  greatly  eroded  strata  basic 
breccias  were  thrown  out,  and  after  these  had  undergone  fresh  erosion  vast  flows  of  rhyolite  covered 
the  country  and  now  form  a  part  of  the  plateau  of  the  Park,  beneath  which  the  northern  extremity 
of  the  Teton  Range  is  hidden. 

Chapter  V.  The  country  described  in  this  chapter  embraces  a  mountainous  area  irregular  in 
outline  and  of  great  diversity  of  form.  It  is  situated  in  the  southern  part  of  the  Park  and  the  Yel. 
lowstone  Park  Forest  Reservation.  It  consists  of  a  number  of  ridges  trending  northwesterly  and 
southeasterly,  formed  for  the  most  part  of  Mesozoie  rocks.  The  older  sedimentary  rocks  are  exposed 
but  the  ridges  are  essentially  made  up  of  sandstones  of  Cretaceous  age.  The  irregular  outline  of  the 
mountains  is  due  to  the  rhyolites  of  the  Park  Plateau  that  abut  against  the  slopes  of  the  upturned 
beds.  The  principal  physical  features  of  the  region  are  Wildcat  Peak  and  Huckleberry  Mountain, 
Bobcat  Ridge,  Big  Game  Ridge,  Chicken  Ridge,  Two  Ocean  Plateau,  and  the  gorge  of  Snake  River. 
West  of  Huckleberry  Mountain  occur  several  exposures  of  dacite  surrounded  by  rhyolite.  They  are 
among  the  few  outcrops  of  dacite  known  in  the  Park,  and  are  apparently  older  than  the  rhyolite.  In 
the  gorge  of  Snake  River  the  Madison  limestones,  Teton  sandstones,  and  the  Ellis  limestones  and 


XVI  OUTLINE  OF  THIS  VOLUME. 

shales  are  well  shown.  The  Snake  River  hot  springs  are  situated  near  the  contact  of  the  rhyolite 
with  the  Carboniferous  limestone,  the  lime  of  the  travertine  being  derived  from  the  Madison  lime- 
stones. The  incrustations  around  the  springs  resemble  the  travertine  deposits  found  at  the  Mammoth 
Hot  Springs.  The  characteristic  and  limited  Wolverine  flora,  of  Laramie  age,  occurs  near  the  base 
of  Pinyon  Peak.  The  conglomerate  of  Pinyon  Peak,  a  striking  physical  feature  of  the  region,  is 
described  as  overlying  unconformably  the  Laramie  sandstones,  and  evidence  is  given  showing  that 
the  conglomerate  probably  belongs  to  Eocene  time,  as  it  iinderlies  the  basic  breccia  of  the  Absaroka 
Range.  The  impressive  gorge  of  Outlet  Canyon  cuts  a  deep  passage  completely  through  Chicken  Ridge. 
The  interesting  feature  of  the  canyon  is  that  it  at  one  time  served  as  the  discharge  for  the  waters 
of  Yellowstone  Lake.  This  sheet  of  water,  which  now  flows  northward  and  drains  to  the  Atlantic 
through  Yellowstone  Canyon,  formerly  discharged  into  Snake  River  and  thence  to  the  Pacific. 
Two  Ocean  Plateau  shuts  in  the  sedimentary  ridges  on  the  east.  The  plateau,  which  rises  10,000 
feet  above  sea  level,  forms  a  part  of  the  Absaroka  range  and  Is  made  up  of  similar  volcanic  breccias 

and  silts. 

Chaptbk  VI.  The  extreme  southern  end  of  the  Snowy  Kange  forms  the  northeast  corner  of  the 

Park.  The  crystalline  core  of  the  range  forms  a  broad,  plateau-like  summit,  bordered  by  sedimentary 
rocks  of  Paleozoic  age,  which  along  the  south  slope  dip  gently  away  from  it  toward  the  Park.  The 
highest  peaks,  together  with  extensive  areas,  are  formed  of  andesitic  breccias,  but  erosion  has  cut 
through  them  and  exposed  the  underlying  limestones,  showing  that  the  volcanic  rocks  rest  upon  a 
very  uneven  anil  rugged  surface.  Detailed  sections  of  the  Paleozoic  sedimentary  rocks  from  the  Flat- 
head formation  to  the  Madison  limestone  are  given,  but  the  igneous  rocks  are  described  in  other 

chapters. 

Chapter  VII.  The  Miocene  volcano  of  Crandall  Basin  built  itself  upon  a  ridge  of  eroded  Pale- 
ozoic rocks  which  dip  toward  the  southwest  from  the  crystalline  schists  of  the  Beartooth  Range. 
Beneath  the  volcano  are  remnants  of  Eocene  breccias  and  lava  flows.  The  volcano  consisted  of  basic 
andesitic  breccias  topped  by  basalt  flows  and  traversed  by  dikes  that  radiated  from  the  stock  or  core 
which  was  the  conduit  beneath  the  crater.  While  bedded  breccias  characterize  the  outer  portions  of 
the  volcano,  chaotic  unbedded  breccias  form  the  central  portion.  Comparison  with  modern  active 
volcanoes  indicates  that  the  Crandall  volcano  rose  to  about  13,400  feet  above  its  limestone  floor.  The 
phanerocrystalline  rocks  within  the  core  are  gabbros  and  diorites,  approaching  monzonites  in  part, 
and  are  chemically  like  the  basalts  and  andesites  of  the  breccias,  dikes,  and  flows,  but  diifer  from 
them  in  mineral  composition.     They  also  are  parts  of  the  volcano  and  are  properly  volcanic  rocks. 

Chapter  VIII.  The  Absaroka  Range  consists  largely  of  volcanic  breccias,  with  subordinate 
amounts  of  massive  flows  or  intrusive  bodies.  This  chapter  presents  a  petrographic  treatment  of  those 
io-neous  rocks  which  lie  withiu  the  limits  of  the  Yellowstone  Park,  and  their  discussion  is  confined  to  an 
account  of  their  field  occurrence  and  distribution  and  a  systematic  description  of  their  mineralogical 
characteristics  and  composition.  The  earliest  accumulations  occur  at  the  northern  end  of  the  range 
and  are  made  up  of  early  acid  breccias  found  in  disconnected  remnants  beneath  early  basic  breccias. 
They  consist  mainly  of  hornblende-andesite  and  hornblende-mica-andesite.  The  early  basic  breccias 
are  pyroxene-andesite,  passing  upward  into  the  massive  basalt  flows.  Upon  the  latter  were  thrown 
the  late  acid  breccias,  similar  in  composition  and  appearance  to  the  early  acid  breccia.  This  passes 
upward  into  late  basic  breccia,  consisting  of  basic  andesites  with  less  basalt  than  is  associated  with 
the  early  basic  breccia.  The  late  basic  breccia  forms  the  southern  portion  of  the  range  within  the 
Yellowstone  Park  and  also  Two  Ocean  Plateau.  At  Sylvan  Pass  and  in  its  vicinity  it  is  traversed  by 
dikes  of  andesite  and  a  few  of  diorite.  Remnants  of  surficial  flows  of  massive  andesite  form  the 
summits  of  Mount  Stevenson,  Mount  Doane,  Colter  Peak,  and  several  prominent  mountains  south  of 
Sylvan  Pass. 


OUTLINE  OK  THUS  VOLUME.  XVII 

t'llAPTEl!  IX.  Certain  b.isultic  Mini  otluT  rocks  assiiriatfd  with  the  andesitic  hrecrias  and 
basalt  Hows  have  a  considerable  content  of  iiitlio(Mase  in  niicrnscci))!!'  crystals,  and  a  comparatively 
high  percentage  oC  potash.  They  occnr  as  lava  Hows  and  as  dikes  in  v.ariiiiis  localities  within  the 
I'ark.  According  to  their  ('honiical  and  niiiicral  composition  tliey  have  been  classed  as  absarokites, 
shoshonitcs,  and  banakites. 

CllAl'TF.R  X.  The  rbVoIites  of  the  I'aiU  are  almost  wholly  extrnsivc  Lavas  of  very  niiiform  compo- 
sition, bnt  having  a  wide  range  of  color,  texture,  and  mog.ascopic  habit.  Tlic  appcar.ancc  of  the  rhy- 
olito  ill  the  field,  and  tlio  microscopical  cliarnctcristics  of  pbcnocrysts,  spheriilites,  litliophys:c,  and 
groniidmass,  are  dencrilied  in  detail.  The  dill'ciont  modidcations  of  cryst.allization,  besides  the  lami- 
nation and  formation  of  pnniicc,  are  referable  to  lieteiogeiieity  of  the  molten  magma,  especially  with 
reference  to  the  amonnt  of  vapor  contained  in  it.  Examples  of  intermingled  b.asalt  and  rhyolite  are 
de.scribed,  in  which  the  basalt  appears  to  have  been  inclosed  and  partly  melted  by  the  rhyolite. 

CiiAPTEU  XI.  The  recent  biisalts  overlie  the  rhyolite  in  most  inst.anccs,  but  .are  found  beneath  it, 
and  also  between  older  and  younger  sheets  of  rhyolite  in  several  localities.  These  basalts  arc  distin- 
guished from  those  .associated  with  the  early  .and  Kate  basic  breccias  by  being  ophitic  .and  iionpor- 
pbyritic  for  the  most  p.art. 

Chapter  XII.  This  chapter  describes  the  Paleozoic  fossils  known  to  occur  in  the  Yellowstone 
Niitional  Park  and  the  Absaroka  Range.  It  is  divided  into  two  sections,  the  first  treating  of  the  Cam- 
brian species  and  the  second  of  the  Devonian  .and  Carboniferous  species.  Both  Flathead  and  GalKatiu 
formaticms  have  yielded  a  sm.all  but  characteristic  fauna.  From  the  Cambrian  21  species  in  all  have 
been  obtained,  several  of  which  are  new  to  science  .and  described  here  for  the  first  time.  No  fossils 
of  undoubted  Silurian  age  have  been  obtained,  altliongh  the  beds  carry  imperfect  and  partially  oblit- 
erated organic  forms.  The  Three  Forks  limestone  has  furnished  a  well-recognized  Devonian  fauna. 
From  the  Madison  limestone  a  varied  fauna  has  been  collected,  but  belonging  wholly  to  the  Lower 
Carboniferous  period. 

CllAPTKU  XIII.  The  Mesozoic  fossils  obtained  from  the  Yellowstone  N.atioual  Park  were  found  in 
the  G.all.atin  Range  near  Electric  Peak,  Teton  Range,  in  the  neighborhood  of  Wildcat  Peak  .and 
Huckleberry  Mountain,  and  from  the  Cret.accous  ridges  in  the  southern  end  of  the  Park  and  Yellow- 
stone Forest  Reserve.  The  Mesozoic  str.ata  have  yielded  78  species  of  invertebrates,  of  which  one  is 
from  beds  supposed  to  be  of  Triassic  age,  4G  are  .Turassie,  and  31  are  Cretaceous.  The  fossils  obtained 
were  mainly  from  the  Ellis  form.atiou  of  the  .Jura  and  the  Colorado  of  the  Cretaceous.  The  .Jnr.assic 
fossils  form  much  the  largest  and  most  prominent  part  of  this  collection,  and  in  number  of  species  it 
compares  favorably  to  the  .Jur.assic  of  other  parts  of  the  Rocky  Mount.ains. 

Chapter  XIV.  The  Mesozoic  fo.ssil  llora  of  the  Yellowstone  National  Park  is  confined  to  the 
Laramie  sandstones  of  the  Cretaceous  .and  is  found  on  Mount  Everts,  near  M.ammoth  Hot  Springs,  and 
at  the  base  of  Pinyou  Peak  near  the  head  of  Wolverine  Creek.  The  llora  from  this  Latter  locality  has 
been  designated  the  Wolverine  Creek  llora.  The  Tertiary  llora  is  very  v.aried  and  possesses  great 
biological  interest.  It  is  a  rich  llora,  and  on  comparing  it  with  the  living  llora  it  becomes  app.areut 
th.at  great  clim.atic  ch.anges  must  have  taken  place  since  the  do.se  of  Miocene  time  to  have  m.ade  these 
changes  in  pl.ant  life  possible.  It  is  found  at  numerous  localities  associated  with  the  breccias  and 
silts  of  the  igneous  rocks  of  the  Absaroka  Range.  It  is  found  in  the  early  acid  breccias,  in  the  early 
basic  breccias,  in  the  late  acid  breccias,  and  in  the  l.ate  basic  lireccias,  where  the  muds  and  silts 
furnish  a  soil  favorable  for  a  vegetable  growth.  The  most  interesting  locality  as  reg.ards  number  of 
species  and  mode  of  occurrence  is  the  well-known  Fossil  Forest  of  .Specimen  Ridge.  The  Terti.ary 
fossil  llora  embraces  about  150  forms  th.at  have  been  distrrbuted  among  .S3  natural  orders.  This  fossil 
flora  is  illustrated  by  forty-five  plates. 
.    MON    XXXII,  PT    II II 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK,  PART  IL 


By  ARNOLD  HAGUE  AND  OTHERS. 


CHAPTER  I. 
DESCRIPTIVE    GEOLOGY    OF   THE    GALLATIN    MOUNTAINS. 


By  Joseph  Paxson  Iddings  aud  Walter  Harvey  Weed. 


I^TTRODUCTION. 

The  Gallatiu  Mountains  form  a  range  of  peaks  and  ridges  extending 
southward  for  63  miles  from  the  vicinity  of  Bozeman,  on  the  line  of  the 
Northern  Pacific  Railroad,  about  latitude  45°  40'.  The  range  lies  between 
the  Yellowstone  and  Gallatin  rivers  and  terminates  in  the  neighborhood  of 
Mount  Holmes,  at  about  latitude  44°  45'.  The  southernmost  18  miles  of 
the  range  lies  within  the  boundary  of  the  Yellowstone  National  Park  aud 
forms  that  portion  of  it  described  in  the  present  chapter.  The  northern 
portion  falls  within  the  region  described  in  folios  1  and  24  of  the  Geologic 
Atlas  of  the  United  States.^ 

Within  the  Park  boundary  the  peaks  of  the  main  chain  reach  altitudes 
of  from  10,000  to  10,500  feet,  and  at  Electric  Peak  11,100  feet,  and  stretch 
from  Electric  Peak,  which  is  situated  directly  on  the  northern  boundary 
line,  southward  to  Mount  Holmes.  The  country  has  been  deeply  cut  by 
erosion,  and  is  drained  by  tributaries  of  the  Yellowstone,  Gallatin,  and 

I  Geologic  Atlas  U.  S.,  folio  1,  Livingston,  Mout.,  1893 ;  and  folio  24,  Three  Forks,  Mont.,  1896. 
MON  XXXII,   PT   II 1  1 


2  GEOLOGY  OF  THE  YELLOWSTOInE  NATIONAL  PARK. 

Madison  rivers,  the  watersheds  between  which  meet  one  another  in  Tln-ee 
River  Peak.  The  special  description  of  the  physiographic  features  of  the 
region,  however,  inchiding  the  glaciation,  will  be  found  in  Part  I  of  this 
report,  where  it  is  treated  by  Mr.  Hague.  Without  entering  into  a  topo- 
graphic description  of  the  Gallatin  Mountains,  it  will  be  in  place  here 
to  call  attention  to  the  fact  that  the  region  in  question,  within  the  Park 
boundary,  is  a  block  of  country  delimited  on  the  east  and  on  the  west  by 
profound  faults  trending  nearly  north  and  south,  the  western  fault  line 
having  a  somewhat  northeasterly  trend.  This  block,  about  7  miles  wide, 
is  bounded  on  the  south  by  a  capping  of  lavas,  which  borders  it  also  to 
some  extent  on  the  east  and  on  the  west.  The  northern  end  of  the  block 
lies  beyond  the  Park  boundary,  in  the  neighborhood  of  Cinnabar  Mountain. 
The  block  is  wider  at  the  south,  and  narrows  northward.  It  is  a  wedge- 
shaped  mass  cut  diagonally  across  a  synclinal  trough,  with  one  long  and 
one  very  short  limb.  The  latter  appears  for  only  a  short  distance  at  the 
northern  end,  in  Cinnabar  Mountain.  Within  the  area  of  the  Park  the 
block  has  the  structure  of  a  monocline,  dipping  northeast  across  the  longer 
diameter  of  the  block.  Minor  faults  and  folds  modify  the  structure  some- 
what and  introduce  local  complications,  which  will  be  described  in  detail. 

As  a  result  of  the  dipping  of  the  block  to  the  northeast,  the  oldest 
formations  are  found  at  the  southern  and  southwestern  ends,  and  the 
youngest  formations  at  the  northern.  The  rocks  are  well  exposed,  the 
succession  of  the  strata  is  clearly  made  out,  and  the  form  and  character  of 
the  igneous  material  that  has  been  forced  through  the  sedimentary  rocks 
are  readily  observed.  The  study  of  the  igneous  bodies  and  their  relations 
to  the  geological  structure  of  the  block  proves  that  the  dynamic  history  of 
this  particular  area  was  complex,  and  extended  over  a  long  period  after  the 
deposition  of  the  coal-bearing  Laramie  sandstones.  In  fact,  a  succession  of 
dislocations  must  have  followed  one  another  through  the  greater  part  of  the 
Tertiary  period.     This  will  aj^pear  from  the  description  which  follows. 

Erosion  has  carved  deeply  the  surface  of  this  upturned,  fractured,  and 
distorted  block,  grooving  it  with  valleys  and  gulches,  the  eastern  system 
trending  northeast  and  east  and  draining  with  the  dip  of  the  strata,  the 
western  system  trending  and  draining  northwest  along  the  general  line  of 
the  strike  and  being  in  all  probability  controlled  by  lines  of  fracture  in 
this  direction.     The  intervening  elevations  rise  abruptly  to  sharp  peaks 


THE  CRAGS.  3 

and  ridges,  attaining  altitudes  of  from  10,000  to  11,000  feet  above  sea  level, 
with  occasional  plateaus,  2,000  feet  or  more  above  the  valley  bottom. 

The  bold  escarpment  and  barren  upper  portions  of  these  mountains 
permit  their  general  structure  to  be  made  out  with  ease,  even  from  a 
distance.  Thus  the  general  structure  of  the  eastern  face  of  the  range  may 
be  seen  from  Bunsen  Peak  or  Ten-ace  Mountain.  The  open,  park-like 
character  of  the  valleys  and  lower  slopes  of  the  mountains,  the  abundance 
of  grass  and  water,  and  the  multitude  of  flowers  that  cover  the  whole 
country  during  the  summer  season  render  this  one  of  the  most  picturesque 
and  delightful  of  mountain  regions,  both  for  the  geologist  and  for  the  artist. 

THE   CRAGS  AISTP   VICINITY. 

A  description  of  the  geological  features  of  the  Gallatin  Range  naturally 
begins  with  an  account  of  the  region  where  the  basal  and  lowest  rocks  of 
the  series  are  exposed.  These  occur  in  the  southern  and  southwestern  part 
of  the  range,  and  a  descrijDtion  of  the  range  from  these  peaks  northward  is, 
in  general,  also  a  description  of  successively  later  geological  formations. 
The  oldest  rocks  of  the  region  are  crystalline  schists,  which  are  mainly 
gneisses.  These  rocks  form  two  prominent  topographic  features  of  the 
southern  end  of  the  range.  The  first  of  these  is  the  group  of  rugged  peaks 
called  The  Crags,  together  with  their  less  elevated  spurs  to  the  south,  and 
their  prolongation  in  the  ridge  trending  northwest,  parallel  to  Grayling 
Creek.  Crowfoot  Ridge  constitutes  the  second  prominent  mass  of  crystal- 
line schists,  while  the  low  rounded  hills  at  the  head  of  Grayling  Creek  are 
also  formed  of  these  rocks.  A  few  inconspicuous  outlying  exposures  of 
schist  occur  to  the  southwest,  where  erosion  has  removed  the  overlying 
sheet  of  rhyolitic  lava. 

THE    CRAGS. 

The  rocky  summits  of  The  Crags  and  the  ridges  northwest  are  very 
rugged  and  difficult  to  traverse  on  account  of  the  loose  ddbris  and  thick- 
timbered  slopes.  But  while  the  southern  escarpment  of  Crowfoot  Ridge  is 
equally  obstructed,  its  summit  is  comparatively  open  and  level  topped, 
showing  little  erosion  since  the  removal  of  the  sedimentary  cover.  The 
lower  hills  between  Grayling  and  Maple  creeks  are  rounded  and  smoothed, 
with  every  evidence  of  having  been  glaciated  and  considerably  worn. 
Tlnroughout  this  area  of  crystalline  schists,  coarse  and  fine  grained  gneisses 


4       GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

alternate  with  one  another,  the  coarser  varieties  being  generally  light- 
colored  mica-gneisses  rich  in  feldspar  and  quartz.  The  finer-grained, 
dark-colored  varieties  are  for  the  most  part  mica-gneisses  richer  in  biotite. 
Mica-schists,  sometimes  highly  garnetiferous,  occur  in  smaller  quantities, 
and  amphibolites  are  also  found.  The  pronounced  lamination  or  schistositv 
of  the  whole  body  of  these  rocks  is  quite  uniform  in  its  jiosition,  the  layers 
standing  at  high  angles  or  nearly  vertical,  with  a  general  north-south 
trend.  The  microscopical  study  of  these  rocks  shows  them  to  be  normal 
crystalline  schists,  having  the  microstructure  of  highly  metamorphosed 
rocks  and  exhibiting  no  traces  of  their  previous  character.  Their  study  in 
the  field  was  not  thorough  enough  to  throw  any  light  on  the  question  of 
their  possible  origin. 

South  and  west  of  The  Crags  the  crystalline  schists  are  directly 
overlain  by  volcanic  breccia  and  tuffs  of  andesites,  whose  subaerial 
accumulation  is  beyond  question.  These  rocks  are  generally  dark  colored, 
and  occur  in  rugged  outcrops  and  rough,  angular  talus  blocks.  In  general, 
the  easterly  slopes  are  smooth,  covered  with  soil,  and  less  steep  than  the 
western  sides  of  the  hills.  The  andesites  are  variegated  in  color  and  are 
chiefly  hornblende-andesite,  carrying  some  pyroxene  and  a  little  biotite. 
The  occurrence  of  these  subaerial  breccias  shows  that  at  the  time  of  their 
eruption  the  crystalline  schists  were  exposed  sui-face  rocks  which  had 
undergone  extensive  erosion,  by  which  they  had  acquired  a  pronounced 
mountainous  topography. 

On  the  west  and  south  the  schists  pass  under  massive  rhyolitic  lava, 
which  is  part  of  the  great  plateau  lavas  farther  south,  and  whose  position 
with  respect  to  the  crystalline  schists  and  andesitic  breccias  is  such  as  to 
show  that  the  rhyolitic  lava  flooded  the  lower  levels  of  this  gneissic  region 
after  the  andesitic  material  had  been  accumulated  and  had  been  partly 
removed  by  erosion.  That  the  rhyolite  overlies  the  andesitic  breccia  is 
clearly  shown  in  the  walls  of  Maple  Creek  Canyon.  The  rhyolite  also  fills 
the  valley  bottom  between  two  ridges  of  andesitic  breccia  in  this  vicinity, 
indicating-  the  extent  to  which  the  andesite  had  been  previously  eroded. 

There  is  marked  contrast  in  the  scenery  and  topography  of  the 
gneissic  areas  and  of  the  country  formed  by  the  rhyolite,  the  former  being 
essentially  rugged  and  broken,  while  the  latter  is  as  yet  comparatively 
little  affected  by  erosion,  the  streams  flowing  in  trenches  and  canyons  cut 


THE  CKAGS.  5 

in  the  soft  rock.     Often  the  boundary  between   gneiss   and   rhyolite  is 
defined  by  small  drainage  ways  woni  along  the  contact. 

Along  the  western  side  of  the  gneissic  area  the  rhyolitic  lava  rises  to 
altitudes  of  8,000  to  8,200  feet,  while  at  the  head  of  Maple  Creek  it  rises 
to  8,700  feet,  the  level  of  the  divide  between  this  creek  and  Grayling 
Creek.  From  this  it  seems  highly  probable  that  the  lava  flooded  the  valley 
of  Grayling  Creek  at  the  time  of  its  eruption,  and  has  since  been  removed 
by  erosion.  The  absence  of  au)^  remnant  of  rhyolite  within  this  valley, 
as  the  map  represents,  is  not  based  on  a  careful  examination  of  the  valley, 
but  expresses  our  ignorance  in  respect  to  its  occurrence  there. 

The  marked  contrast  between  the  topographic  character  of  the 
southern  side  of  Crowfoot  Ridge  and  that  of  the  northern  side  is  note- 
worthy. The  southern  slopes  are  almost  free  from  lateral  spurs  of  any  size 
and  the  ridge  is  approximately  straight.  On  the  north,  spurs  branch  off  at 
short  intervals,  increasing  in  size  toward  the  west  until  they  attain  the 
proportions  of  mountain  ridges.  The  tlu-ee  most  prominent  of  these  spurs 
trend  north. 

This  contrast  in  topographic  configuration  is  to  be  explained  by  the 
position  of  the  former  covering  of  sedimentary  rocks,  which  were  removed 
during  the  downcutting  of  the  Grayling  Creek  Valley.  This  creek, 
following  the  well-known  habit  of  streams,  formerly  cut  its  channel 
westward  along  the  strike  of  the  northward-dipping  sedimentary  rocks, 
gradually  deepening  its  channel  until,  reaching  the  underlying  crystalline 
schists,  it  was  compelled  to  continue  in  the  same  course,  deepening  and 
widening  the  valley,  whose  straight  northerly  walls  are  due  to  the  absence 
of  lateral  drainage  channels  consequent  upon  the  northward  dip  of  the 
strata.  The  same  configuration  is  seen  in  the  upper  valley  of  the  Gallatin 
River  and  the  valley  of  Fawn  Creek,  where  the  mountain  gorges  are  cut 
in  sedimentary  rocks. 

The  topography  of  this  vicinity  is  so  closely  dependent  on  the  charac- 
ter and  position  of  the  strata  immediately  overlying  the  gneiss,  and  these 
strata  have  been  tilted,  curved,  and  faulted  to  such  an  extent,  that  it  is 
advisable  to  postpone  the  description  of  this  area  until  the  less  distributed 
rocks  lying  immediately  east  of  the  main  body  of  crystalline  schists  have 
been  described. 

The  region  just  mentioned  lies  east  of  the  main  gneissic  area,  and  is 


6  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK, 

separated  from  it  by  a  fault  trending  a  little  west  of  north.  This  fault 
crosses  the  southern  end  of  Crowfoot  Ridge,  about  a  mile  west  of  the 
summit  of  Three  River  Peak,  and  passes  southward  along  the  west  base  of 
the  mountains,  between  Indian  and  Maple  creeks,  disappearing  beneath  the 
more  recent  rhyolitic  lavas.  The  eastern  area  embraces  the  most  joromi- 
nent  peaks  of  the  southern  portion  of  the  Gallatin  Mountains,  including 
Mount  Holmes  and  the  bare  porphyry  peaks  around  the  head  of  Indian 
Creek,  besides  Trilobite  Point,  The  Dome,  Antler  Peak,  and  Three  River 
Peak,  peaks  that  are  directly  connected  with  the  mountains  north  of  Panther 
Creek. 

CROWFOOT    SECTION. 

Before  taking  up  the  description  of  these  mountains,  involving  sedi- 
mentary rocks,  it  will  be  best  to  give  an  account  of  the  stratigraphic  series. 
A  very  carefully  measured  section  was  made  of  the  Paleozoic  strata  exposed 
on  a  northern  lateral  spur  of  Crowfoot  Ridge.  This  high  mountain  ridge 
shows  the  entire  sequence  of  the  Paleozoic  sediments  of  the  region,  from  the 
crystalline  schists  to  the  top  of  the  Carboniferous,  exposed  in  an  unbroken 
succession  of  apparently  conformable  beds  dipping  at  an  angle  of  30°  N. 
The  general  form  and  profile  of  the  ridge  is  shown  in  PL  II,  which  gives  a 
view  of  the  ridge  from  the  east.  The  illustration  shows  the  bluffs  formed  by 
the  harder  beds  of  the  series,  rising  above  the  slopes  into  which  the  shales 
and  thinl)^  bedded  strata  have  weathered  down.  Two  lines  of  cliffs,  formed 
by  the  mottled  limestone.  No.  14  of  the  section,  and  the  Jefferson  limestone. 
No.  19,  are  seen  in  the  view.  These  horizons  form  characteristic  cliffs 
throughout  the  range,  and  are  an  important  aid  in  reading  the  structure  of 
the  mountains.  The  section  of  the  sedimentary  rocks  made  at  this  place 
has  served  as  a  basis  of  comparison  for  all  the  other  sections  of  the  Paleozoic 
rocks  made  in  the  Gallatin  Range.  The  beds  are  well  exposed,  the  crest  of 
the  ridge  being  bare  of  soil  or  vegetation  and  the  trend  of  the  ridge  being 
very  nearly  at  right  angles  to  the  strike  of  the  strata. 


THE  GALLATIN  MOUNTAINS. 


Grotrfoot  Ridge  section. 

Nuinber.  ^eet. 
33  Quailiaiit  qnartzite.     Siindstono  and  ([uartzito,  saccharoidal  in   texture,  reddish  near 
the  base,  with  daik-gray  and  very  calcareous  layers;  passes  at  top  to  a  white  sand- 
stone   200 

d.  Limestone, light  gray,  brecciat(Hl  and  broken;  in  places  iron  stained 100 

c.  Limestone,  light  gray,  varied  with  brown  baiidsor  fiuestripes  antl  lines;  contains 

chert,  and  is  in  ])lace8  breeciated,  the  fragments  being  cemented  by  calcite 400 

b.  Limestone;   crystalline,   very  light  gray,  weathering  creamy  white;   contains 

white  chert  in  bands  and  nodules 30 

a.  Limestone,    crystalline,  dark    brownish   gray,  intersected  with   calcite  seams. 

Chert  bands  and  nodules  are  abundant 125 

655 

Limestone,  light  gray  and  gray,  weathering  gray ;  banded  with  brown ;  banded  appear- 
ance on  weathered  surface ;  finely  crystalline.    Fossils  abundant 380 

'  b.  Limestone,  crystalline,  massive,  light  gray,  with  small  brownish  fossil  fragments  scat- 
tered through  it.  The  upper  10  feet  is  a  conglomerate  of  red,  often  cellular  lime- 
stone.    Fossils iO 

a.  Limestone,  massive,  light  gray,  similar  to  No.  28 15 


31' 


31 


30 


Is 


29  Limestone,  light  gray  and  brown,  very  finely  crystalline  or  granular;  well  bedded, 
with  layers  10  to  20  feet  thick  of  brown  or  cream-colored  limestone.  Certain  layers 
are  banded  with  light-colored  chert,  weathering  bufi'  or  brown;  these  layers  carry 

corals  and  fossil  shells 85 

28    Limestone,  crystalline,  light  gray,  generally  massive,  but  in  places  more  thinly  bedded, 

and  striped  with  brown.     The  rock  is  often  magnesian  and  impure.     Fossils 200 

27  Limestone,  dark  gray  and  butf,  very  argillaceous,  thick  and  thinly  bedded.  Fossils 
from  the  upper  portion  and  the  lower  portion  of  these  beds  are  Lower  Carboniferous. 

This  limestone  is  very  much  like  the  bed  beneath  it 50 

b.  Limestone,  more  massively  bedded  than  the  underlying  bed  and  coarser  in  crystal- 
lization; a  quite  pure  limestone,  full  of  fossil  fragments 15 

26  \  a.  Limestone,  fissile  and  thinly  bedded,  impure  and  argillaceous.     The  fossils  occur 

in  lower  and  upper  beds 60 


I 


75 


r 

^-a 

SS 

hS 

20 1 

^<ti 

OJH, 

25    Limestone,  coarsely  crystalline,  dark  gray,  somewhat  variable;  a  little  cherty;  fossil- 

iferous - 80 

24  Limestone,  cherty;  at  base  very  finely  crystalline;  occurs  in  massive  layers  and  is 
pinkish  gray.  Higher  up  the  beds  are  cherty,  and  the  upper  portion  contains  many 
crinoid  stems  and  a  few  indistinct  corals  and  shells.     Weathers  red,  and  is  cracked 

and  breeciated 60 

23    Limestone,  bnff  and  red,  fissile,  near  base  passing  into  a  more  thickly  bedded  limestone. 

The  rock  is  a  dense,  compact,  light  limestone,  argillaceous  and  siliceous 30 

22    Limestone,  crystalline,  dense,  compact;  the  upper  20  feet  is  red  and  cracked;  the  beds 

beneath  .ire  massive,  with  toothed  junction  surfaces.     Eock  is  decidedly  magnesian..     50 
21    Limestone,  in  alternating  beds  of  thin  and  fissile  buff  and  massive  gray  limestones, 
the  l)eds  15  to  20  feet  thick,  and  the  limestone  much  cracked    This   limestone  is 

impure,  argillaceous,  and  in  some  beds  quite  arenaceous 100 

b.  Limestone,  crystalline,  dark  gray,  thick  and  thinly  bedded,  with  fetid  odor,  and 

C(mtaining  gasteropod  shells.     The  limestone  is  quite  pure 15 

a.  Limestone,  crystalline,  brown,  crackled,  with  fetid  odor.     Slightly  arenaceous ; 

granular 10 

25 


GEOLOGY  OF  THE  YELLOWSTONE  NATIO]!f AL  PAEK. 


Number. 


19  i 


Crowfoot  Bidge  section — Continued. 

Limestone,  gray  mottled  with  black,  crystalline,  in  part  magnesian,  well 
lieilded,  in  jilaces  crackled,  and  with  much  iron  oxide  and  calcite.  Strike 
N.70^  W.     Dip  30^  N 70 

Limestone,  mottled,  gray  and  buff,  very  ferruginous  in  places.     Beds  5  feet 

thick 30 

Limestone,  white,  crystalline,  weathers  cream,  with  granular  surface  and 
indistinct  fossil  traces ;  is  magnesian  and  very  finely  crystalline.  Forms  a 
cliff,  and  is  iron  stained  in  places 35 


Feet. 


O 


a 


18  Limestone,  conglomerate,  nodular,  and  shaly  layers  near  the  base,  overlain  by  thick  and 
thin  beds  of  densely  crystalline  limestone  alternating  with  thinner,  shaly  and  fissile 
strata.     Toward  the  upper  part  less  shaly,  denser,  with  brown  layers  and  layers  of 

very  fossiliferous,  crystalline  limestone 

17     Shale,  calcareous,  thin;  purple,  green,  and  brown 

16    Limestone,  very  argillaceous,  buff  brown,  very  fissile  . .  -    

15     Shale,  greenish  gray,  very  soft  and  crumbly 

14  Mottled  limestone.  The  upper  2  feet  is  an  arenaceous  conglomerate,  in  which  the  frag- 
ments are  rounded  pebbles  of  shale  and  sandstone;  the  matrix  a  slightly  argillaceous 
sandstone.  Strike  N.  70°  W.  Dip  27^  N.  The  mottled  limestone  is  a  pure,  thickly 
bedded  (20  feet)  rock,  dark  gray  mottled  with  browu   or  black;  crystalline,  with 

granular  weathered  surface  of  unchanged  color 

'  13  Limestone,  variously  moditied.  The  lower  layers  thickly  and  thinly  bedded,  much  of  it 
coarsely  crystalline,  with  green  grains  of  glanconite  and  great  numbers  of  trilobite 
spines.  luterbedded  with  this  limestone  are  layers  of  dense,  gray,  fissile  and  thinly 
bedded  limestone,  with  yellow  bands,  and  limestone  conglomerate.  About  the  middle 
of  the  beds  there  are  several  thick  beds  of  crystalline  limestone  containing  green 
"•rains.     This  is  overlain  by  a  conglomerate.     The  matrix  is  pure  limestone,  the  pebbles 

slightly  argillaceous  and  resembling  a  mud  deposit 

12    Shale,  very  thin,  olive  green  and  dark  purple 

11  Limestone,  pure  and  ferrnginous.  In  general  this  limestone  is  red-brown,  but  contains 
masses  of  dense,  dark-colored  limestone,  which  weather  in  balls  with  spherical  shells. 

Balls  3  feet  through 

f  Limestone  conglomerate;   brown-gray  and  gray  pebbles  in  buff  matrix.     Fragments'! 

j      well  rounded I 

I  Limestone,  very  similar  to  No.  9,  and  taking  section  to  base  of  long  ridge.     Over  these  | 

I     beds  are  layers  of  crystalline  limestone,  with  green  grains J 

9    Limestone,  buff  mottled  with  brownish  gray;  thinly  bedded 

8    Limestone,  massivelybedded,  quite  pure;  weathers  with  smooth  surface;  color,  brown. 
7    Limestone,  pure  gray,  with  dense,  dark-gray  layers  and  streaks  in  a  buff,  granular  j 

matrix.    Runs  up  to  top  of  first  point  shown  in  PI.  II J 

6    Limestones,  thinly  bedded,  light  and  dark  gray  in  color,  showing  remains  of  shells  and 

trilobites 

5    Limestones,  thinly  bedded,  with'  interbedded  micaceous  shale,  having  fossil  indications. 

Fossils  collected  from  the  upper  part  and  from  lowest  beds 

4    Shale,  micaceous,  green  and  purplish 

3    Sandstones,  slightly  indurated,  red  and  green,  with  grains  well  rounded;  quartzose 

2    Quartzite  and  sandstones,  cross  bedded,  and  containing  well-rounded  pebbles  of  gneiss. 
1    Gneiss. 


135 


40 
5 


55 


100 
150 


10 


50 


175 


10 

60 

75 

30 

100 


THE  GALLATIN  JMOINTAINS.  9 

MOUNTAINS   SOUTH   OF   PANTHER  CREEK. 

The  geological  structure  of  the  mountains  east  of  the  fault  already 
mentioned  as  crossing  Crowfoot  Ridge  is  somewhat  complicated  by  the 
presence  of  large  bodies  of  igneous  rock  that  have  been  forced  between, 
and  also  across,  tlie  sedimentary  strata.  The  exact  position  of  these 
eruptive  masses  will  appear  from  the  description  and  may)  (PI.  X).  In 
general,  the  stratified  rocks  form  a  flat  arch,  the  central  portion  of  which  is 
nearly  horizontal,  and  beneath  which  the  crystalline  schists  are  exposed 
along  the  east  base  of  the  mountain  escarpment  for  a  distance  of  4  miles. 
The  strata  immediately  overlying  these  schists  at  the  northern  end  dip  at  a 
low  angle,  5°,  toward  the  northeast,  and  at  the  southern  end  they  dip  about 
3°  toward  the  southwest.  This  is  the  simple  structure  of  the  eastern  portion 
of  the  area  along  a  line  through  Antler  Peak,  The  Dome,  Trilobite  Peak, 
and  the  hills  south  of  Winter  Creek,  which  is  shown  in  the  geological  cross 
section,  PI.  Ill,  fig.  1. 

The  igneous  magma  which  was  intruded  into  the  shaly  layers  of  the 
Flathead  formation  and  was  afterwards^  consolidated  as  the  Indian  Creek 
laccolith,  was  forced  upward  from  some  source  at  the  north,  uplifting  the 
strata  southward  and  wedging  them  apart,  and  being  itself  separated  into 
two  sheets  by  a  thin,  wedge-shaped  layer  of  limestone.  The  sheets,  which 
are  nearly  horizontal  for  a  considerable  distance,  become  thinner  southward 
and  have  only  a  slight  thickness  where  last  exposed  in  this  direction.  In  the 
ridge  north  of  Indian  Creek  the  sedimentary  rocks  overlying  the  intruded 
body  arch  over  it  from  east  to  west  in  a  pronounced  manner,  which  is  shown 
in  cross  section  in  PL  III,  fig.  2,  and  which  will  be  described  later  on. 

Subsequent  to  the  intrusion  of  this  double  sheet  of  igneous  rock,  there 
was  another  outbreak  of  molten  magma  of  a  slightly  different  character, 
which  was  forced  upward  directly  through  the  rocks  just  described.  The 
manner  of  its  intrusion  is  shown  by  the  nature  of  the  contacts  between 
the  second  eruptive  mass  and  the  surrounding  rocks.  This  body  forms 
a  great  mass,  whose  present  exposure  is  3  miles  long  and  2  miles  wide, 
embracing  the  six  white  peaks  surrounding  the  head  of  Indian  Creek,  of 
which  Mount  Holmes  is  the  most  conspicuous.  With  this  preliminary 
sketch  before  us,  it  is  possible  to  2)i'0ceed  to  a  more  detailed  description  of 
the  geology  of  this  portion  of  the  country. 


10      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

SOUTH    END    HILLS. 

Commencing  with  the  most  sontheru  end  of  the  eastern  part  of  the 
ridge,  where  the  sedimentary  rocks  begin  to  rise  above  the  rhyolite  plateau, 
we  find  hmestone  exposed  on  the  crest  of  the  low  ridge  3J  miles  soiith  of 
Mount  Holmes.  The  bedding  is  nearly  horizontal,  the  dip  being  but  3°  to 
5°  SW.  throughout  tlie  greater  part  of  the  ridge.  The  character  of  the 
limestone  varies  from  shaly  and  fissile  to  massive  beds,  the  highest  strata 
being  mottled  and  banded,  dark  and  light  gray,  and  in  places  conglomeratic. 
The  lithological  characters  are  like  those  of  the  Cambrian  formations  about 
300  to  600  feet  above  the  base  of  the  series  as  it  exists  in  the  section  north 
of  Crowfoot  Ridge. 

At  the  southwestern  extremity  of  the  southern  end  of  this  ridge  there 
is  a  small  exposure  of  coarse-grained  gneiss,  against  which  lies  a  bed  of 
fine-grained  granular  quartzite,  about  50  feet  thick,  over  which  is  light -gray 
limestone  in  apparent  conformity.  The  highly  inclined  position  of  these 
beds,  dipping  70°  NE.,  with  strike  N.  50°  W.,  and  the  nearly  horizontal 
position  of  the  limestone  a  short  distance  east,  indicate  a  fault  between 
these  two  sets  of  beds,  which  probably  trends  northwest  and  southeast, 
with  hade  to  northeast,  and  with  a  downtlu-ow  of  not  more  than  500  feet. 
The  extension  of  the  fault  could  not  be  traced  on  account  of  the  covering 
of  lava. 

The  igneous  rock  intruded  between  the  limestone  and  shales  already 
mentioned  is  the  thin  edge  of  one  of  the  sheets  of  the  Indian  Creek 
laccolith,  and  may  be  called  andesite-porphyiy.  At  the  northern  end  of 
the  ridge  in  question  it  is  exposed  in  a  cliff  100  feet  high,  which  is  about  the 
thickness  of  the  sheet  in  this  place.  Limestone  is  exposed  beneath  and 
also  above  it.  The  inti'usive  sheet  can  be  traced  for  several  miles  southward, 
becoming  thinner,  until  it  is  but  10  feet  thick  where  last  seen,  before 
disappearing  beneath  the  rhyolite  of  the  plateau.  Above  it,  on  the  highest 
portion  of  the  ridge,  two  small  dikes  of  andesite-porphyry  traverse  the 
limestone  across  the  axis  of  the  ridge.  A  short  distance  to  the  southwest 
there  is  a  narrow  vertical  dike  of  similar  rock,  about  3  feet  wide,  trending 
southwest  and  northeast.  It  rises  slightly  above  the  shaly  surface  of  the 
ground  and  exhibits  two  systems  of  inclined  joints,  forming  rhombic  hori- 
zontal columns.     Near  the  sides  of  the  dike  a  third,  horizontal  joint  splits 


TRILOBITE  POINT.  11 

the  rock  into  hexagonal  cohimns,  which  are  well  defined  near  the  outside 
of  the  dike,  but  disap2)ear  toward  the  center.  The  rock  is  dark  colored 
and  dense  near  the  contact  walls,  becoming  lighter  colored  and  less  dense 
toward  the  center,  and  containing  irregular  vesicular  cavities,  flattened 
parallel  to  the  walls  of  the  dike. 

Direct  connection  between  the  fonnations  of  this  ridge  and  those  of 
the  mountains  north  is  obscured  by  the  rhyolite  lava  which  extends  up 
Winter  Creek  and  across  the  saddle  of  the  divide  to  Maple  Creek.  A  close 
coirespondence,  however,  between  the  sections  of  limestones  and  the  intru- 
sive sheets  is  observed  on  both  sides  of  Christmas  Tree  Park,  and  when  the 
dip  of  the  strata  in  each  case  and  the  altitudes  at  which  similar  horizons  are 
exposed  are  taken  into  account,  it  appears  that  the  rocks  on  both  sides  of 
the  valley  were  continuous,  with  low  southerly  dip,  before  the  valley  was 
eroded  and  filled  with  rhyolite,  or  that  a  very  slight  fault  has  dropped  the 
strata  of  the  ridge  just  described  a  few  hundred  feet.  In  the  diagi-am  of 
cross  sections,  PI.  Ill,  fig.  1,  the  strata  are  drawn  as  though  not  faulted. 

TRILOBITE  POINT. 

At  the  south  and  east  base  of  the  group  of  peaks  directly  connected 
with  Mount  Holmes,  including  Trilobite  Point  and  The  Dome,  crystalline 
schists  are  exposed  at  altitudes  of  from  8,000  to  8,500  feet,  and  in  isolated 
localities  at  8,700  feet.  These  outcrops  form  a  low,  rounded  bench  at  the 
base  of  the  mountains,  the  upper  limit  of  the  gneiss  being  highest  at  the 
south,  and  lowest  in  elevation  north,  in  the  bottom  of  Indian  Creek.  The 
isolated  exposures  near  the  head  of  Winter  Creek  are  close  to  the  margin  of 
the  great  intrusive  mass  of  Mount  Holmes,  and,  though  at  about  the  same 
altitude  as  the  other  outcrops,  show  by  the  dip  of  the  neighboring  stratified 
rocks  that  their  position  has  been  disturbed  by  the  intrusion  of  this  igneous 
^  mass.  The  limestones  dij?  steeply  in  various  directions,  and  the  beds  are 
largely  concealed  by  drift,  the  outcrops  being  small  and  disconnected,  so 
that  the  precise  stratigraphic  structure  was  not  apparent  at  this  locality. 
The  map  represents  the  beds  as  continuous  with  those  to  be  described  in 
Trilobite  Point,  though  they  are  in  fact  locally  disturbed  by  the  intru- 
sion of  the  Holmes  mass. 

The  character  of  the  crystalline  schists  is  like  that  of  the  area  about 
The  Crags — coarse-grained  gneisses,  mostly  micaceous,   with  subordinate 


12  GEOLOGY  OF  THE  YELLOWSTOISI E  NATIONAL  PARK. 

amount  of  schists  and  some  ancient  and  metamorphosed  intrusive  bodies; 
the  more  detailed  account  of  which  is  given  in  Part  I  of  this  monograph. 

Along  the  eastern  base  of  the  mountains  the  gneiss  forms  prominent 
exposures,  constituting  the  end  of  the  long  southeast  spur  of  Trilobite  Point 
and  forming  bold  escarpments  on  either  side  of  the  valley  northeast  of 
Mount  Holmes,  below  the  level  of  the  glacially  carved  lake  basins.  The 
gneiss  forms  a  bench  extending  along  the  eastern  base  of  The  Dome,  the 
exposure  having  a  height  of  300  or  400  feet,  and  occurring  across  the  valley 
of  Indian  Creek,  where  it  is  last  seen  to  form  a  low,  wooded  hill  on  the 
northern  side  of  the  creek. 

Immediately  overlying  the  gneiss  around  three  sides  of  Trilobite  Point 
is  the  lower  sheet  of  andesite-porphyry,  a  light-gray  aphanitic  rock  with 
porphyritical  crystals  of  feldspar,  hornblende,  and  biotite.  The  sheet  is 
between  200  and  300  feet  thick  and  occupies  the  horizon  of  the  Flathead 
shales,  being  overlain  by  150  to  200  feet  of  Cambrian,  Flathead  Hmestone 
in  nearly  horizontal  beds.  Above  the  limestone  is  another  sheet  of  andes- 
ite-porphyry, from  100  to  200  feet  thick,  which  in  turn  is  topped  by  the 
Upper  Cambrian  shale  and  trilobite-bearing  limestone.  The  upper  surface 
of  the  uppermost  sheet  of  andesite-porphyry  is  quite  irregularly  defined, 
and  the  overlying  limestone  is  traversed  by  small  dikes  and  veins^  of  igne- 
ous rock,  that  are  in  part  offshoots  from  the  lighter-colored  igneous  mass  of 
Mount  Holmes.  The  basal  (lower)  sheet  of  andesite-porphyry  is  thicker 
at  the  northern  side  and  thimier  at  the  southern  side  of  the  mountain. 

At  the  saddle  on  the  ridge  connecting  Trilobite  Point  with  Mount 
Holmes,  near  the  contact  of  the  rocks  just  described  with  the  igneous  rock 
of  the  latter  mountain,  the  beds  of  limestone  and  andesite-porphyry  are 
turned  up  to  an  angle  of  about  45°,  dipping  eastward,  away  from  the 
Holmes  mass.  The  strata  are  greatly  fractured  and  are  penetrated  by  many 
small  bodies  of  the  Holmes  rock. 

THE   DOME.  • 

The  Dome  is  a  mountain  siimmit  northeast  of  Mount  Holmes  and  con- 
nected with  it  by  a  low  ridge.  It  is  separated  from  Antler  Peak  and  the 
northern  portion  of  the  range  by  the  wide  and  deep  valley  of  Indian  Creek. 
The  mountain  is  largely  formed  of  andesite-porphyry,  an  extension  of  the 
Indian  Creek  laccolith,  which  rests  upon  crystalline  schists  and  is  capped 
by  Cambrian  limestones  forming  the  summit  of  the  peak.     A  thin  belt  of 


OS  GEOLOGICAL  SURVEY 


MONCGRAPK  xzxi:  PAP-T ::  7-L  :" 


MOUNT  HOLM  ES 


ANTLER  PEAK 


QUADRANT  MOUNTAIN 


GRAY  PEAK 


ELECTRIC  PEAK 


Jftgn 


ELECTRIC  PEAK 


BANNOCK  PEAK 


ANTLER   PE 


CROWFOOT  ridge: 


THREE    PI  Vf.R    PEAK 


«gn 


Section  11-^ 


MOUNT    HOLMES 


BANNOCK   PEAK 


GRAY  PEAK 


01-()I,()(iU  AJ,  SIXTIONS  ACKOSS  CAI.LAIIN  l(AN(il'; 
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INDIAN  CREEK  LACCOLITH.  13 

these  limestones  is  also  included  in  the  laccolithic  mass  separating  the  igne- 
ous rock  into  the  two  sheets,  whose  southward  extension  has  already  been 
noted  at  Trilobite  Point  and  the  South  End  Hills. 

On  the  southern  side  of  the  mountain  the  lower  intruded  sheet  rests 
directly  upon  the  crystalline  schists,  and  as  we  pass  up  the  southern  slope 
of  the  mountain,  which  is  precipitous  in  places,  we  find  a  layer  of  limestone 
about  300  feet  thick,  which  is  not  wholly  continuous.  Above  it  are  several 
hundi'ed  feet  of  porphyry,  and  then  a  bluff  wall  of  200  feet  of  limestone 
that  forms  the  surface  of  the  table-topped  portion  of  the  mountain,  upon 
which  rises  a  cone  of  limestone  400  feet  in  height.  The  limestone  has  a 
slight  dip  southward,  which  brings  the  porphyry  out  at  a  higher  altitude 
on  the  northern  side  of  the  peak.  The  character  of  the  limestone  overlying 
the  porphyry  is  the  same  as  that  of  the  limestone  on  the  northei-n  side  of 
Indian  Creek,  which  occurs  in  the  same  position,  and  which  has  been  iden- 
tified as  Middle  Cambrian.  As  these  beds  approach  the  eruptive  mass 
forming  the  peak  southwest  of  The  Dome,  they  turn  up  abruptly  to  a  steep 
angle,  dipping  away  from  it  toward  the  northeast  at  55°. 

The  steep  northern  face  of  The  Dome,  below  the  fiat  top,  is  almost 
wholly  andesite-porphyry  to  within  300  feet  of  the  bed  of  the  creek;  the 
lower  part  being  limestone,  forming  steep  walls  that  rise  above  a  bench  of 
g-neiss.  A  thin  belt  of  shale  or  limestone  occurs  about  halfway  up  the 
slope,  inclosed  in  the  porphyry.  It  does  not  appear  to  be  continuous 
horizontally,  though  quite  persistent.  The  contact  between  the  rocks  just 
described  and  the  inti'usive  mass  to  the  west  is  sharply  marked  and  nearly 
vertical,  and  will  be  described  in  connection  with  the  occurrence  of  that 
rock  body. 

The  limestone  underlying  the  andesite-porphyry  at  the  northern  base 
of  The  Dome  is  in  nearly  horizontal  beds,  but  at  the  eastern  base  of  the 
mountain  the  gneiss  rises  up  and  cuts  it  off.  At  a  higher  altitude  the  lime- 
stone is  exposed  with  a  steep  westerly  dip,  evidently  bent  and  faulted,  with 
a  throw  of  several  hundred  feet.  At  about  this  place  the  lower  sheet  of 
porphyry  cuts  down  to  the  horizon  of  the  gneiss. 

INDIAN   CREEK  LACCOLITH. 

North  of  the  valley  of  Indian  Creek  the  slopes  rise  steeply  upward  to 
the  base  of  a  wall  or  cliff  that  extends  westward  from  the  eastern  face  of 
the  mountains  to  the  head  of  Indian  Creek  Valley.     The  lower  part  of  this 


14      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

great  wall  is  formed  of  nearlj^  horizontal  beds  of  limestone  (Flathead),  upon 
which  rests  the  great  mass  of  intrasive  audesite-porphyry  whose  southei'n 
extension  has  already  been  noted,  and  over  which  arches  the  distinctly 
bedded  limestone  that  forms  the  eastern  ^jart  and  the  summit  of  Antler 
Peak.  This  is  the  great  intrusion  termed  by  W.  H.  Holmes  the  "Indian 
Creek  laccolite,"^  whose  mass  forms  the  greater  part  of  Antler  Peak,  the 
bold  summit  north  of  Indian  Creek,  and  its  extension  westward  to  the 
slopes  of  Three  River  Peak.  The  structure  and  topogi'aphy  of  this  part  of 
the  ridge  are  clearly  shown  in  the  sketch  by  Mr.  Holmes."  In  the  middle 
of  the  ridge  the  overlying  strata  are  absent,  but  at  the  western  end  of  the 
ridge  they  recur,  completing  the  westward-dipping  limb  of  the  arch,  as 
shown  in  PI.  Ill,  fig.  2. 

This  dome-shaped  body  of  intrasive  rock  is  a  cross  section  of  the 
double  sheet  met  with  in  the  mountains  south.  In  Antler  Ridge  it  attains 
its  maximum  thickness,  and  appears  as  one  massive  body  with  a  thin  layer 
of  shale  or  limestone  inclosed  near  its  middle,  which  is  indicated  in  Mr. 
Holmes's  sketch.  It  is,  however,  not  absolutely  continuous.  No  doubt  it 
is  the  thin  edge  of  the  limestone  wedge  that  split  the  intrusive  mass  in  two 
as  it  was  forced  southward. 

An  examination  of  the  limestone  underlying  the  laccolith  shows  that 
the  prominent  cliff,  75  to  100  feet  high,  is  formed  of  the  nodular  limestones 
of  the  Flathead  formation  corresponding  to  the  lower  limestone  belt  of  the 
Crowfoot  section.  These  beds  are  more  fully  noted  in  the  section  of  the 
sedimentary  rocks  of  Antler  Peak.  Within  the  lowest  micaceous  shale 
beneath  the  laccolith  there  occurs  a  layer  of  white,  lithoidal,  igneous  rock, 
50  feet  thick,  and  evidently  a  horizontal  sheet,  which  is  again  exposed  at 
about  the  same  horizon  2  miles  farther  west.  Petrographically  it  resembles 
the  rock  of  Mount  Holmes,  of  which  it  is  probably  an  offshoot. 

The  contact  between  the  lower  massive  limestone  and  the  bottom  of 
the  laccolith  is  plainly  exposed  in  places.  The  limestone  exhibits  little  or 
no  metamoi-j^hism,  there  being  only  a  slight  lightening  of  its  color  along 
the  immediate  contact.  The  crude  columnar  jointing  of  the  massive  lime- 
stone may  have  been  the  result  of  baking  by  the  laccolithic  mass,  but  it  is 
not  pronounced ;  however,  it  may  easily  be  mistaken  at  a  distance  for  the 

'  Twelfth  Ann.  Rept.  U.  S.  Geol.  and  Geog.  Surv.  Terr,  (for  1878),  Pint  II,  Washington,  1883. 
^  Op.  cit.,  PL  XIII,  p.  24. 


INDIAN  OREEK  LACCOLITH.  15 

well-known  jointing'  of  igneous  rock.  The  limestone  and  shale  inclosed 
within  the  body  of  the  laccolith,  also  show  almost  no  evidence  of  meta- 
morphism  other  than  a  lio-htening-  of  their  color  in  innnediate  contact  with 
the  })orphyry.  The  inclosed  stratum  of  limestone  is  20  to  40  feet  thick, 
and  rather  persistent.  It  is  nearly  horizontal,  or  arches  gradually  with  the 
curve  of  the  laccolith  dome.  Several  masses  of  red  and  gi'een  shale,  tilted 
at  high  angles,  were  seen  in  the  igneous  rock.  These  are  probably  blocks 
of  the  heavier  shale  belt  forming  the  upper  part  of  the  Flathead  formation, 
and  which  is  the  horizon  in  which  the  laccolith  appears  to  have  been 
intruded.  There  are  also  small  fragments  of  limestone  and  gneiss  included 
in  the  porphyry,  caught  up  in  its  passage  through  the  lower  rocks  which 
were  ruptured  at  the  time  of  its  intrusion. 

The  laccolith  sheet  thins  out  eastward  under  Antler  Peak,  disappearing 
near  the  base  of  the  eastern  slope,  where  the  upper  and  lower  limestone 
strata  meet  and  foi-m  the  whole  of  the  northeast  spur  of  the  mountain, 
dipping  at  the  low  angle  of  about  6°  NE.  The  apparently  gradually 
increasing  dip  of  the  overlying  limestoiies  as  they  arch  over  the  laccolith  is 
found  on  investigation  to  be  irregular,  the  dips  varying  along  the  cliflPs 
forming  the  bare  southern  exposure,  increasing  from  5°  to  10°,  and  farther 
west  to  20°,  then  becoming  nearly  horizontal  just  before  reaching  the 
depression  on  the  ridge.  There  is,  however,  a  northerly  element  of  the 
dip  which  is  not  noticeable  on  the  southern  exposure.  Where  the  dip 
changes  noticeably,  the  limestone  is  shattered  by  innumerable  small, 
vertical  faults,  close  together;  it  thus  behaved  as  a  brittle,  not  as  a  plastic, 
mass  at  the  time  of  the  laccolithic  intrusion.  The  overlying  limestone 
embraces  the  upper  part  of  the  Cambrian  formations,  including  the  massive 
mottled  limestone  which  is  the  base  of  the  Gallatin  limestones,  together 
with  the  bai'ren  strata  that  represent  the  Silurian  and  Devonian,  and  about 
400  feet  of  the  Carboniferous,  which  forms  the   summit  of  Antler  Peak. 

The  laccolith  is  about  1,200  feet  thick  at  the  middle,  where  it  forms  a 
high  point  projecting  into  the  valley  of  Indian  Creek.  Here  the  limestone 
capping  has  been  removed  by  erosion,  leaving  the  slope  of  the  ridge  to 
indicate  about  the  slope  of  the  old  plane  of  contact.  The  triangular  peak 
northwest  of  this  point  shows  the  overlying  limestones  dipping  at  2°  to  3° 
NW.  and  extending  down  the  long  divide  to  Bighorn  Pass,  where  they 
dip  over  the  porphyry  for  a  short  distance  at  10°  and  also  at  25°  NW., 


16      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK, 

the  generally  low  dip  recumng  again  farther  north.  At  Bighorn  Pass  the 
laccolith  thins  out  and  reaches  its  western  limit. 

In  Three  River  Peak  the  porphyry  is  also  overlain  by  limestone  in 
nearly  horizontal  beds  with  slight  westerly  dip,  the  uppermost  strata 
belono'ing'  to  the  Madison  limestones  of  the  Carboniferous. 

Along  the  western  boundary  of  the  laccolith,  between  Three  River  Peak 
and  Bighorn  Pass  at  the  head  of  Gallatin  River  Valley,  the  limestone  strata 
dip  W.  45°,  becoming  less  inclined  farther  west,  where  they  encounter  a 
fault  trending  west  of  north,  which  brings  them  against  gneiss  and  steeply 
tilted  Cambrian  beds.  Unfortunately  the  strata  bordering  the  laccolith  on 
the  north,  along  the  bottom  of  Panther  Creek  Valley,  are  covered  with 
loose  material  from  the  mountain  slopes;  hence  the  position  of  the  rocks 
adjacent  to  the  laccolith  on  the  north  was  not  discovered.  In  several 
places  the  porphyry  has  broken  up  through  the  overlying  limestone. 

Without  entering  too  minutely  into  the  petrographical  character  of 
the  laccolith  of  andesite-porphyry,  which  will  be  described  in  detail  in 
Chapter  II,  it  may  be  well  to  mention  some  of  its  general  characteristics. 
The  andesite-porphyry  is  a  light-gray  to  whitish  aphanitic  rock  with  many 
small  phenocrysts  of  feldspar  and  fewer  of  biotite  and  hornblende.  It 
forms  massive  outcrops  intersected  by  joints  in  all  directions,  and  the  rock 
splits,  upon  weathering,  into  sherdy,  angi;lar  fragments.  In  only  one  place 
was  columnar  jointing  noted — on  the  southeast  spur  of  The  Dome.  In  the 
central  part  of  the  laccolith  the  groundmass  of  the  rock  has  a  crystalline 
texture,  though  extremely  fine  grained.  Near  the  margin  the  rock  gi'ows 
denser  and  darker  colored.  The  same  is  true  where  the  sheets  become 
thinner  toward  the  south.  The  extent  of  this  mass  in  exposure  is  shown 
on  the  map,  and  its  relation  to  the  suiTOunding  rocks  is  given  in  the 
cross  sections. 

MOUNT  HOLMES  BYSMALITH. 

A  great  mass  of  igneous  rock,  3  miles  long  and  2  miles  wide,  forms 
Mount  Holmes  and  the  ridge  north  to  the  summit  of  the  peak  west  of  The 
Dome,  and  extends  across  the  head  of  Indian  Creek  and  constitutes  the 
chain  of  four  peaks  west  of  this  creek  and  south  of  Three  River  Peak.  This 
great  body  of  igneous  rock  breaks  up  through  the  sedimentary  strata  as  a 


BYSMALITHS.  17 

core  or  plug.  It  is  a  type  of  intrusion  for  which  the  name  bysmahth  has 
been  proposed.^ 

A  laccoHth  as  defined  by  Gilbert^  is  a  body  of  igneous  rock  which  has 
insinuated  itself  between  two  strata  and  opened  for  itself  a  chamber  by 
lifting  all  the  superior  beds.  A  symmetrical  dome-shaped  body  is  the 
exceptional  or  ideal  form,  and,  as  Cross''  has  pointed  out,  Gilbert's  use  of  the 
term  practically  included  all  thick  lenticular  masses  of  intrusive  igneous 
rock  occurring  at  a  certain  geological  horizon  in  a  sedimentary  complex. 
Cross  includes  under  the  term  laccolith  all  masses  in  which  the  expansion  of 
the  body  has  taken  place  from  a  plane  approximately  parallel  to  the  bedding, 
and  says  that  numerous  causes  may  affect  the  regularity  of  the  form. 
Of  these  the  principal  are:  (1)  Oblique  position  of  the  plane  of  expansion 
to  bedding  planes  of  the  sediments;  (2)  lines  of  structural  weakness  in  the 
strata;  (3)  presence  of  earlier  intrusions;  (4)  lack  of  coherence  and  of 
pronounced  bedding  in  strata  invaded.  These  factors,  we  understand,  simply 
modify  the  form  of  the  laccolith,  whose  essential  characters  are  those 
described  by  Gilbert.     They  can  not  in  any  sense  replace  the  latter. 

A  laccolith  is  distinguished  from  an  intrusive  sheet  of  igneous  rock, 
which  is  an  intrusion  between  strata  accompanied  by  a  certain  amount  of 
lifting  of  the  superincumbent  rock.  The  difference  lies  in  the  thickening 
of  the  igneous  body  into  a  more  or  less  lenticular  mass  in  the  case  of  a 
laccolith,  over  which  the  strata  arch ;  whereas  the  upper  and  lower  surfaces 
of  a  sheet  are  almost  parallel  to  each  other.  In  sheets  the  lateral  dimen- 
sions are  very  great  as  compared  with  the  depth  or  thickness;  in  laccoliths 
the  difference  between  the  thickness  and  the  lateral  dimensions  is  much  less. 

Cross  has  shown  that  a  certain  amount  of  vei'tical  displacement  may 
accompany  the  arching  of  the  overlying  strata,  as  in  the  laccolith  of  Mount 
Marcellina,^  without  changing  the  general  character  of  the  intrusion.  But 
where  vertical  displacement  with  faulting  is  one  of  the  chief  characteristics 
of  the  intrusion,  a  distinction  from  normal  laccolithic  intrusion  should  be 
recognized.     In  the  extreme  this  would  result  in  the  forcing  upward  of  a 

'  Iddings,  J.  p.,  Bysmaliths :  Jour.  Geol.,  Vol.  VI,  1898. 

-Gilbert,  G.  K.,  Report  on  the  Geology  of  the  Henry  Mountaius,  U.  S.  Geog.  and  Geol.  Surv. 
Rocky  Mountain  region  (J.  W.  Powell  in  charge),  1877,  p.  160,  PI.  V. 

^  Cross,  Whitman,  The  laccolithic  mountain  groups  of  Colorado,  Utah,  and  Arizona :  Fourteenth 
Ann.  Rept.  U.  S.  Geol.  Survey  (for  1892-93),  1895,  p.  236. 

■•Loc.  cit.,  p.236. 
HON  XXXII,  PT  II 2 


18      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

more  or  less  circular  cone  or  cylinder  of  strata,  having  the  form  of  a  plug, 
which  might  be  driven  out  at  the  surface  of  the  earth  or  might  terminate  in 
a  dome  of  strata  resembling  the  dome  over  a  laccolith.  By  this  mode  of 
intrusion  the  vertical  dimension  of  the  intruded  mass  becomes  still  greater 
as  compared  with  the  lateral  dimensions,  so  that  the  shape  is  more  that  of  a 
plug  or  core.  Such  an  intruded  plug  of  igneous  rock  may  be  termed  a 
hysmalith  (/JiSayuai^plug,  Az9o?— stone).  We  have,  then,  transition  from 
a  flat,  thin,  intrusive  sheet  to  a  laccolith  with  lenticular  form,  and  from 
this  to  a  bysmalith  with  much  greater  depth  and  considerable  vertical 
displacement. 

Examples  of  bysmaliths  are  not  common  as  yet.  RusselP  has  called 
attention  to  what  he  considers  volcanic  plugs  in  the  region  of  the  Black 
Hills  of  Dakota,  and  has  suggested  their  recognition  as  types  of  intrusion 
different  from  normal  laccoliths.  A  sharp  discrimination  of  the  two  types 
may  not  always  be  possible,  since  they  grade  into  each  other,  as  in  Mount 
Marcellina.  In  the  intrusive  bodies  of  Mount  Holmes  and  the  Indian 
Creek  laccolith  the  contrast  is  sufficiently  marked  and  the  two  types  are 
well  illustrated.  Nearly  two-thirds  of  the  circumference  of  the  Holmes 
mass  is  exposed  as  a  nearly  vertical  plane  of  contact  crossing  almost  hori- 
zontal strata.  The  western  boundary  is  against  gneiss  and  along  a  fault 
plane  of  considerable  magnitude,  which  probably  acted  as  the  conduit 
throuo-h  which  the  mao^ma  was  forced.  There  is  no  means  of  knowing 
what  may  be  the  shape  of  the  bottom  of  this  bysmalith.  It  is  possible 
that  it  may  have  risen  through  the  fault  fissure  until  it  encountered  the 
sedimentary^  strata  resting  upon  the  gneiss,  witli  its  inclosed  laccolith.  It 
may  have  spread  laterally  along  shaly  strata  near  the  gneiss  and  beneath 
the  laccolith;  then  its  movement  laterally  may  have  been  checked,  for 
the  pressure  upward  became  sufficient  to  rupture  the  strata  and  laccolith 
and  to  force  a  mass  of  these  rocks  covering  an  area  of  over  5  square  miles 
up  more  than  2,000  feet — probably  more  than  twice  that  height. 

The  areal  relation  of  the  Mount  Holmes  bysmalith  to  the  surrounding 
terranes  is  shown  on  the  geological  map,  PI.  X.  The  vertical  relations  are 
shown  in  the  profile  sections  of  the  Gallatin  Mountains,  PI.  Ill,  fig.  3,  and 
PI.  IX,  fig.  4,  and  in  PI.  V,  figs.  1,  2,  3,  which  are  profile  sections  through 
Echo  Peak  and  Three  River  Peak,  and  through  The  Dome  and  the  peak 

1  Russell,  I.  C,  Jour.  Geol.,  Vol.  IV,  1896,  p.  23. 


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MOUNT  HOLMES  HYSMALITH.  19 

southwest,  and  tlirougli  Mount  Holmes  and  Trilobite  Point.  These  cross 
tlie  contact  i)lane  between  the  bysmaUtli  and  the  strata  with  the  inclosed 
laccolith. 

Owing  to  the  crystalline  character  of  the  rock  constituting  the  bys- 
malitli,  there  is  little  doubt  that  it  soliditied  beneath  a  covering  of  strata. 
The  crystals  are  larger  than  those  forming  the  mass  of  the  Indian  Creek 
laccolith.  A  possible  reconstruction  of  the  position  of  the  strata  after  the 
intrusion  is  given  in  PI.  V,  fig  4,  in  which  all  of  the  formations  up  to 
the  top  of  the  coal-bearing  Laramie  are  represented — a  total  thickness  of 
9,000  feet. 

The  upper  parts  of  the  mountains  into  which  this  intrusion  has  been 
carved  are  barren  and  rocky  above  9,000  feet,  with  comparatively  smooth 
slopes  covered  with  loose  fragments  of  porphyry.  The  peaks  are  pointed 
in  some  cases  and  rounded  in  others,  as  may  be  seen  from  PI.  IV.  The 
rock  is  very  uniform  in  appearance  throughout  the  entire  extent  of  the 
mass.  It  is  light  gray  to  white,  aphanitic  to  fine  crystalline,  with  a  slightly 
porphyritic  structure  in  part.  It  shows  small  flakes  of  biotite  and  indistinct 
phenocrysts  of  feldspar.  It  is  massive,  with  irregular  joint  ci'acks,  and 
weathers  into  angular  blocks  and.  slabs.  Its  megascopical  chai'acters  are 
quite  uniform  throughout  the  greater  part  of  the  mass,  which  varies  slightly 
in  grain.  But  near  the  margin  of  the  body  the  rock  becomes  denser  and 
more  aphanitic,  showing  a  broad  banding  parallel  to  the  walls  of  contact 
with  the  surrounding  rocks.  These  walls  are  nearly  vertical  in  the  moun- 
tain west  of  The  Dome,  on  the  saddle  east  of  Mount  Holmes,  and  also  on 
that  of  Echo  Peak.  In  all  cases  examined,  the  neighboring  limestones  dip 
away  at  angles  of  40°  to  55°,  and  the  adjacent  andesite-jiorphyry  has  been 
crushed  an<l  dislocated.  It  is  reddened  and  in  places  is  filled  with  veins 
and  apophyses  from  the  dacite-porphyry,  which  is  clearly  proved  to  be  an 
intrusion  subsequent  to  that  of  the  Indian  Creek  laccolith.  Its  western 
border  in  contact  with  the  crystalline  schists  is  obscured  by  debris,  being 
located  at  the  base  of  the  mountains.     These  relations  are  shown  in  PI.  V. 

The  eruption  appears  to  have  taken  place  along  the  fault  line  that  lies 
west  of  Three  River  Peak.  There  seems  to  be  no  break  in  the  continuity  of 
the  bysmalith  mass,  and  this  fact  indicates  that  it  was  intruded  at  one  time. 
The  vertical  displacement  of  a  mass  of  rock  2^  miles  long  and  2  miles  wide,  by 
what  appears  to  have  been  a  single  act,  is  remarkable.  The  peti'ographical 
character  of  the  rock  is  that  of  an  intrusive,  not  a  surficial,  body ;  hence. 


20      GEOLOGY  OF  THE  YELLOWSTOJ^E  NATIONAL  PARK. 

we  may  assume  that  it  did  not  reach  the  surface  of  the  earth,  but  was 
covered  by  the  sedimentary  rocks  it  displaced.  The  same  kind  of  por- 
phyry occurs  in  two  small  bodies  about  3  miles  farther  north,  along  the 
Crowfoot  fault  line,  west  of  Three  River  Peak.  Hei-e  they  have  broken 
into  Carboniferous  limestone,  which  otherwise  in  this  region  is  quite  free 
from  intrusions  of  igneous  rock. 

Still  another  small  intrusion  occurs  along  the  northern  border  of  the 
Indian  Creek  laccolith,  but  is  confined  to  the  upper  horizon  of  the  Cam- 
brian rocks.  It  is  a  dark  basic  porphyry  of  an  unusual  character,  with 
occasional  phenocrysts  of  hornblende,  mica,  and  feldspar.  It  forms  a  small 
sheet,  50  to  75  feet  thick,  exposed  on  the  divide  south  of  Bighorn  Pass  and 
along  the  south  base  of  Bannock  Peak.  It  was  not  found  in  contact  with 
the  laccolith,  and  the  relative  times  of  their  intrusion  were  not  made  out. 
There  is  no  rock  similar  to  it  in  the  reg-ion  explored,  except  a  small  sheet 
in  Three  River  Peak,  and  nothing  approaching  it  in  composition  occurs 
nearer  than  Electric  Peak. 

ANTLER   PEAK. 

The  sedimentary  rocks  overlying  the  Indian  Creek  laccolith,  as  already 
noted,  form  the  summits  of  Antler  and  Three  River  peaks;  stratigraphic 
sections  wei'e  made  at  both  these  localities.  Antler  Peak  is  the  prominent 
summit  lying  between  The  Dome  and  the  flat-topped  mass  of  Quadi-aut 
Mountain.  (See  PI.  VI.)  The  greater  part  of  the  mountain  is  formed  of 
the  intrusive  mass  of  the  Indian  Creek  laccolith,  as  just  described.  The 
sedimentary  rocks  are  best  exposed  on  the  southern  side  of  the  mountain 
and  at  the  eastern  slopes,  where  the  laccolithic  rock  passes  beneath  the 
limestones. 

The  gneiss  is  exposed  on  the  low  wooded  hill  at  the  southeast  base  of 
the  peak,  indicated  on  the  map  by  the  8,000-foot  contour.  This  hill  and  the 
slopes  back  of  it  are  covered  heavily  with  drift,  which  usually  conceals  the 
gneiss  and  the  overlying  stratified  rocks;  there  being  no  exposures  except 
near  the  base  of  the  great  limestone  ledge  which  forms  such  a  prominent 
feature  of  the  valley.  The  strata  were  examined  where  the  ledge  has  been 
cut  through  by  a  small  stream  channel  from  the  summit,  the  debris  which 
elsewhere  conceals  the  foot  of  the  wall  having  here  been  washed  away. 
The  lowest  strata  exposed  were  thinly  bedded  limestones  and  rather  heavy 


ANTLER  PEAK.  21 

iiig'  ill 
was  made  at  this  place: 


micaceous  beds  containing'  indistinct  traces  of  fossils.     The  following-  section 


Indian  Creek  section. 

Crowfoot   Nimi- 

section.      brr.  Feet. 

Laccolith,  ande8ite-)ii>r])liyry. 

11  6.    Liinestoiic,  rather  tliiuly  bedded,  dark  bliic-gray  with  lighter  weathered  surface.  6 

7-10  5.    Limosloiies,  f'oiuiing  the  great  ledge  of  the  monutaiii  side.     Many  beds  are  of  a 

crystalline,  fine-grained,  dark-gray  and  dense  limestone  seamed  with  calcite. 

Weathers  light  gray,  often   rusty.     At  the  base  is  thinly  bedded,  breaking 

readily  into  small  angular  pieces.     At  top,  beds  are  slightly  cherty  and  fossil- 

iferous.     In  ci'ntcr,  beds  are  massive  and  appear  irregularly  bedded.     Strike 

N.Si*^  E.  and  dip  3'^  N 225 

Dacite-porphyry,  probably  an  offshoot  of  the  Holmes  bysmalith 25 

6  4.   Limestone,  compact,  brown,  weathering  gray 20 

5  3.   Slialy  beds,  micaceous  and  schistose,  with  thin  bands  of  limestone 50 

2-4  2.    Interval,  no  exposure 300 

1  1.   Gneiss. 

It  will  be  seen  from  the  above  section  that  the  andesite-porphvry  of 
the  laccolith  immediately  overlies  the  limestone  No.  6  of  this  section,  which 
con-esponds  to  the  Flathead  limestones  of  the  Crowfoot  Ridge  section. 
The  laccolith  has  therefore  been  intruded  in  the  upper  shale  belt  of  the 
Flathead  formation,  the  shales  being  150  feet  thick  in  the  Crowfoot  section. 
The  occurrence  of  the  laccolithic  intrusion  is  the  same  at  the  base  of  Tliree 
River  Peak,  where  above  the  porphyry  a  part  of  the  shales  is  found 
beneath  the  limestones  that  form  the  highest  beds  of  the  Flathead  forma- 
tion. 

At  Antler  Peak  the  laccolith  incloses  parts  of  the  Flathead  limestones, 
as  well  as  a  thin  belt  of  limestone  and  fragments  of  the  underlying  shale. 
Along  the  base  of  steeper  slopes  toward  the  northeast,  the  drift  has  covered 
all  exposures;  even  the  beds  of  the  great  limestone  ledge  are  partially 
hidden.  Over  these  beds  we  find  a  platform  where  the  overlying  shale  and 
poi-phyry  have  been  eroded,  leaving  the  limestones  underneath  intact.  That 
the  bench  is  due  to  the  erosion  of  the  shale  seems  probable;  easilj^  yield- 
ing to  disintegrating  agencies,  it  has  been  carried  away,  undermining  the 
porphyry,  which  has  also  been  swept  off  by  glacial  action. 

The  lowest  bed  noted  above  the  laccolith  is  a  finely  crystalline,  light- 
di-ab  limestone,  probably  the  upper  beds  of  the  Flathead  limestone  of  the 
general  section.  The  following  succession  of  strata  is  exposed  on  the 
northeast  spur  of  the  mountain  from  the  summit  of  the  peak  down  to  this 
bed: 


22 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


Crowfoot 
aectioD. 


31 


S 


g1 


30(1,6 
29 


26o 

25 
24 


27,  28  <  22 


Num- 
ber. 

81 


21 
20 


Antler  Peak  section. 

Limestone,  crystalline,  moderately  dense,  brown,  weathering  grayish,  witli 
rough  pitted  surface,  and  breaking  readily  into  small  angular  pieces.  Dip, 
N.  .50    E.,  20= 

Limestone,  less  splintery  than  bed  above,  light  brown,  fissile,  with  fossil  layers. 

Limestone,  finely  crystalline,  light  gray  with  buff  or  pink,  finely  granular, 
weathered  surface.     Very  fissile,  plates  warped 

Limestone,  brown  or  purplish  brown,  very  fissile  and  platy.     Fossils  abundant. 

Limestone,  massively  bedded,  light  drab  and  brown,  breaking  readily  into  frag- 
ments.    Fossils  somewhat  abundant.     Dip,  5"  NE 

Limestone,  finely  crystalline,  light  and  dark  gray  and  gray-brown,  weathering 
bntf,  with  smooth,  finely  granular  surface.  Layers  thickly  and  thinly  bedded, 
with  very  fissile  fossiliferous  strata  near  base 

Limestone,  mottled,  massive,  and  seamed  with  calcite.  Lenticular  arrangement 
of  light-brown  in  darker  mass  gives  appearance  of  bedding 

Limestone,  very  fissile  and  containing  fossils 

Limestone,  massive,  purple,  containing  white  fossil  fragments 

Limestone,  alternating  layers  of  very  fissile,  gray,  and  fossiliferous  limestone 
and  more  massive  rock 

Limestone,  coarsely  crystalline,  without  chert;  is  fossiliferous  and  seamed  with 


;alcite 


Cherty  limestone,  forming  a  prominent  ledge  shown  in  Holmes's  sketch.  Hard, 
dense,  crystalline;  contains  corals  and  crinoid  stems  and  much  blue  chert  in 
bands  and  nodules.     The  rock  is  somewhat  seamed  with  calcite 


Feet. 


100 
40 

15 

100 

50 


100 

15 

5 

15 

170 

50 

100 


23 


22 


21 


20 


19c 


19 


18 


17 

16 

15 
14 
13 

111 


Limestone,  somewhat  massive  and  thickly  bedded  (5  to  10  feet),  light  gray,  with 
lifht,  very  rough,  and  irregular  weathered  surface.  Few  fossils  and  a  little 
light-colored  chert 40 

Limestone;  alternating  beds  of  dense  light-drab  limestone  and  brown  arena- 
ceous sandstone,  with  rough  and  pitted  weathered  surface  and  fetid  odor,  parts 
of  it  resembling  No.  16  of  this  section.  Extends  up  to  base  of  cone  top.  The 
rock  is  an  arenaceous  limestone,  dark  brown-gray,  weathering  brown 130 

Limestone,  compact,  dense,  hard,  dark  gray,  weathering  very  light  brown-gray, 

with  finely  granular  surface 20 

Limestone,  dark  brown-gray,  weathering  straw-color  and  rich  brown.     Is  an 

arenaceous  limestone 5 

Limestone,  white,  pitted  and  rotted,  with  harder  mottled  places 6 

Interval,  no  exposure 10 

Limestone,  brown,  dense 5 

Limestone,  light  creamy  yellow  mottled  with  gray,  thinly  bedded,  breaking  into 

small  cuboidal  blocks.     Strike,  N.  5°  W.     Dip,  3°  W 35 

Limestone,  finely  crystalline,  white 30 


15-19fc  10    Limestones,  grading  at  top  into  cherty  limestone. 
14  9    Mottled  limestone,  but  30  feet  exposed 


I- 


(11 


8    Interval,  no  exposure. 

7    Limestone,  finely  crystalline,  light  drab. 


160 
50 


THREE  ElVEB  PEAK. 


23 


West  of  the  eastern  summit  the  edges  of"  the  lower  beds  outcrop,  and 
the  Galhitin  Hmestone  is  exposed  in  the  saddle.  On  the  northeast  spur  of 
the  peak  the  Flathead  limestones  are  exposed,  the  dip  being-  N  30°  E.,  10°. 

THREE   RIVER  PEAK. 

Three  River  Peak  is  a  shaq)  point  whose  position  at  the  head  of  the 
Gallatin  River  and  of  branches  of  the  Gardiner  and  Madison  rivers  makes 
the  name  appropriate.  The  slopes  rise  abruptly  from  the  head  of  Indian 
Creek  Valley  on  the  east,  while  to  the  north  an  almost  vertical  wall  rises 
above  the  deep  blue  waters  of  Gallatin  Lake.  The  peak  occurs  on  the 
western  side  of  the  Indian  Creek  laccolith,  and  the  beds  composing  it,  like 
those  forming- the  summit  of  Antler  Peak,  consist  of  Paleozoic  strata  ranging 
from  the  Cambrian  limestones  to  those  of  the  Carboniferous.  The  sedi- 
mentary rocks  are,  however,  penetrated  by  several  sheets  of  intrusive  rocks 
which  are  much  decomposed,  but  represent  phases  of  the  Mount  Holmes 
bysmalith.  The  following  section  shows  the  sequence  of  rocks  exposed 
on  the  northern  spurs  of  the  peak  from  Indian  Creek  Pass  to  the  summit:     . 

Three  River  Peak  section. 


Crowfoot  Num- 
seetion.      ber. 


26a 

2.T 


.12 

in 


10 


24 


n^ 


«g 


03  J 


23 


21-22 


15-20 


.U 


13 


r  3 


f 


Feet. 
75 
30 
15 
25 

30 
5 

35 

50 
10 
17 
5 
25 
Limestone,  thinly  bedded,  dark  and  light  gray,  magnesiau 130 

Limestones,  in  a  series  of  beds,  not  individually  noted 160 

Limestonfl,  thinly  bedded 70 

Mottled  limestone,  matrix  light  brown,  mottled  with  black;  due  to  aggrega- 
tion of  black  grains  of  matrix 40 

Gray,  blue-gray,  brown,  and  black  limestones,  with  layers  of  "glaueonitic" 
limestone,  the  grains  black  instead  of  green.  Is  fosaillferous.  Thickly  and 
thinly  bedded,  with  some  yellow  argillaceous  layers  and  one  conglomerate 
bed 100 


12    Limestone,  crystalline,  gray,  fossiliferous;  contains  crinoid  stems 

Limestone,  light  gray,  dense,  massive,  cherty 

Porphyry,  fissile,  much  decomposed,  yellow  and  purple 

Limestone,  light  gray 

Porphyry,  fissile,  decomposed  and  yellow  at  base ;  upper  half  massive  and 

fresher 

Limestone,  crystalline,  light  gray,  with  granular,  weathered  surface 

Limestone,  brownish   gray,   weathering  a  light  brown;   massively  bedded; 
with  splintery  fracture 

Porphyry,  light  colored,  nearly  white,  weathering  brown,  fissile;  thoroughly 

decomposed 

Limestone,  baked  by  porphyry 

Porphyry,  fissile,  yellow  and  rusty  gray,  thoroughly  decomposed 

Limestone,  black  and  rusty,  much  baked 

Porphyry,  dense,  compact,  looking  like  quartzite 


24  GEOLOGY  OF  THE  YELLOWSTOI^E  NATIONAL  PARK, 

The  shores  of  the  Galhxtin  Lake,  and  the  small  hills  adjoining,  are 
formed  of  the  laccolith  rock,  audesite-porphyry.  The  western  boundary 
of  this  rock  runs  northward  along  a  gully,  west  of  the  di-ainage  from  the 
lake,  and  through  a  small  shallow  pond  to  the  saddle  of  Bighorn  Pass.  To 
the  south  the  porphyry  extends  to  the  base  of  Three  River  Peak  in  the  rear 
of  the  lake,  and  forms  the  saddle  in  the  pass  between  Indian  Creek  and 
the  valley  of  the  Gallatin  River;  from  here  northward  the  exposure  extends 
along  the  western  base  of  the  ridge  to  Bighorn  Pass. 

The  position  of  the  strata  seen  in  the  precipitous  northern  face  of 
tins  peak  is  shown  in  PI.  VII.  At  the  western  base  of  this  mountain  they 
dip  sharply  over  the  edge  of  the  laccolith,  changing  from  nearly  horizontal 
to  50°  or  70°  W.,  and  gradually  decreasing  again  westward.  Into  the  axis 
of  this  abrupt  bend  a  vertical  offshoot  from  the  andesite-porphyry  has  been 
intruded,  showing  that  the  limestones  were  ruptured  at  this  place. 

The  limestone  strata  of  Three  River  Peak  are  traversed  by  dikes  of 
lithoidal  igneous  rock  at  various  angles.  One  broad  dike,  100  feet  thick  in 
places,  cuts  diagonally  across  the  northern  face,  appearing  on  the  eastern 
slope  about  halfway  up  to  the  si;mmit.  Another,  about  10  feet  thick, 
without  phenocrysts,  lies  horizontally  between  the  strata  and  might  easily 
be  mistaken  for  a  compact  sandstone.  A  narrower  dike  cuts  nearly 
verticallv  throuo-h  the  western  side  of  the  mountain. 

At  the  west  base  of  the  peak  the  gneiss  is  faulted  against  the  lime- 
stones by  the  soutliern  extension  of  the  Gallatin  fault.  The  position  of  the 
sedimentary  beds  which  abut  against  the  gneiss,  as  well  as  their  fracturing, 
shows  clear  evidence  of  the  presence  of  the  fault.  An  intrusive  body  of 
igneous  rock  related  to  the  Mount  Holmes  rock  occurs  at  this  locality. 

On  the  saddle  between  Three  River  Peak  and  Echo  Peak,  near  the 
contact  of  the  Holmes  bysmalith  with  the  andesite-porphyry  and  lime- 
stone, the  latter  rocks  are  seen  to  have  been  turned  up,  so  as  to  dip  40° 
N.,  away  from  the  bysmalith,  and  to  be  greatly  shattei'ed  and  dislocated, 
producing  slickensides  and  a  pulverizing  of  the  rock  along  the  fracture 
planes. 

BIGHORN   PASS. 

Bisrhorn  Pass  is  a  low  divide  between  the  head  waters  of  the  Gallatm 
River  and  the  drainage  of  Panther  Creek,  and  affords  an  easy  passage  from 
the  valleys  west  of  the  mountains  across  the  range  to  the  central  region  of 


EIGIJOUN  I'ASS.  25 

the  Park.  The  pass  is  cut  in  the  Paleozoic  sedimentary  rocks,  which  are 
sH^htly  tihed  by  an  intruded  sheet  of  andesite-i)orphyry  that  is  the 
northern  extension  of  the  Inchan  Creek  hiccohth.  A  dark,  Liinprophyric 
rock  occurs  at  the  lowest  })oint  in  the  pass,  where  it  is  seen  to  form  a  sheet 
50  feet  thick  intrusive  in  the  Cambrian  shales.  The  hjoh  ridgfe  extending 
north  from  the  head  of  Indian  Creek  to  Bighorn  Pass  is  formed  of  sedi- 
mentary beds  that  overlie  the  northward  extension  of  the  Indian  Creek 
laccolith.  Above  the  andesite-])orpliyry  of  the  laccolith  which  forms  the 
Indian  Creek  Pass  the  green  Flathead  shales  are  exposed,  overlain  by 
the  upper  limestone  series  of  the  Flathead,  which  are  here  100  feet  thick 
and  resemble  quite  closely  the  beds  of  this  horizon  as  developed  in  Crow- 
foot Ridge.  The  summit  of  the  ridge  is  formed  of  the  Gallatin  "mottled 
limestone,"  which  dips  to  the  northwest  and  makes  a  well-defined  ledge, 
with  a  cliff"  face  30  feet  high  and  a  rounded  but  hummocky  surface,  -the 
result  of  glacial  planing.  Near  Bighorn  Pass  the  beds  are  locally  affected 
by  an  intrusion  of  the  laccolith,  and  dip  more  steeply  than  the  beds  north 
of  the  pass,  there  being  a  difference  of  5°  to  8°.  Two  sections  of  the 
Paleozoic  rocks  were  measured  in  this  vicinity;  the  first  was  made  on  the 
ridge  running  south,  the  second  from  Bighorn  Pass  to  the  summit  of 
Bannock  Peak.  These  sections  show  the  following  sequence  of  beds, 
arranged  in  descending  order: 

Bighorn  Pass  section. 

Crowfoot       Num- 
section.         ber.  Feet. 


^J 


H 


"-5 


Cherty    sandstones    .and   limestones,   brown    and   gray,  chert   nodules,   witli 
whitened  surface 


11 


21     Quartzose  conglomerate ;  matrix  a  light-gray  limestone 20 

33      20    White  beds  of  sandstone,  quartzite,  and  limestone,  generally  saccharoidal 325 

32  19  Limestone,  crystalline,  light  colored.  The  upper  portion  is  a  brecciated  and 
nearly  pure  limestone.  The  lower  beds  are  dense,  finely  crystalline,  weath- 
ering white,  with  granular  surface.  Magnesian,  and  containing  sparsely 
disseminated  chert.     Strike,  S.  30^  W.;  dip,  10°  NW 275 

32      18    Limestone,  very  finely  crystalline,  with  calcite  strings,  brown,  dense,  massive; 

nearly  pure 25 

31  17  Limestone,  breccia ;  the  matrix  is  similar  to  the  bed  below ;  the  fragments 
resemble  the  beds  above  and  below.  The  lower  beds  are  slightly  siliceous, 
light-gray  limestones  weathering  pale  yellow 50 

31  16  Limestone,  crystalline,  light  brown,  with  granular  weathered  surface;  mass- 
ively bedded,  and  is  vertically  jointed  and  contains  some  chert  in  bands 75 


26 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


29 


28 


Bighorn  Pass  section — Continued. 

Crowfoot       Num- 
sectioD.         ber.  Feet. 

30  15  Cherty  limestone.  The  lower  30  feet  ia  a  brown  fossiliferous  limestone,  over- 
lain by  70  feet  of  a  moderately  coarsely  crystalline  gray  rock,  weathering 
brownish.  One  bed  is  a  compact  brown  limestone,  full  of  criuoul  stems 
and  fossil  fragments,  which  appear  as  crystalline  masses  of  calcite  on  fresh 
fracture,  but  on   weathered  surface  show  their  true  nature.     The  upper 

portion  of  No  15  is  cherty  and  massive 225 

14     Limestone;   the  lower  portion  light  brown,  shading  to  gray;   massive,  with 
cherty  band  near  center.     The  upper  part  Is  rich  in  coral.     This  limestone 

varies  in  crystallization,  being  both  fine  and  coarse 30 

13     Limestone,  gray,  weathering  brown,  finely  crystalline  and  compact 12 

12    Limestone,  linely  crystalline,  white,  cherty.     Chert  is  light  gray,  weathering 

rusty  or  black 5 

11     Limestone,  blue,  finely  crystalline,  very  splintery 6 

10    C'hprty  limestone,  white,  finely  granular 30 

9e  Limestone,  coarsely  crystalline,  light  drab,  with  few  fossils;   runs  down  to 

saddle 25 

9b  Limestone,  finely  crystalline,  compact,  massively  bedded,  light  drab,  vertically 

jointed.     Dip  18-,  N.  20^  W 20 

9a  Limestone,  very  light  gray,  coarsely  crystalline,  containing  crinoid  stems  and 

other  fossils 50 

8     Limestone,  snmewhat  coarsely  crystalline,  compact,  white;  the  base  concealed 

by  talus  of  No.  9  of  this  section 30 

7     Limestone,  fine  grained,  fissile,  dark  gray,  weathering  blue;   certain  layers 

are  quite  fossiliferous 90 

27  6  Limestone,  dark  gray,  often  brownish  gray;  cherty  and  siliceous  near  base. 
The  upper  50  feet  more  friable  and  soft;  contains  numerous  fossils,  shells, 
crinoid  stems,  and  corals 250 

5  Limestone ;  finely  crystalline,  with  quartzose  band  near  top ;  gray,  weather- 
ing creamy.     The  top  is  concealed  by  the  talus  of  No.  6,  and  the  thickness 

should  be  increased  about  40  feet iO 

4    Limestune,  dense,  massive,  dark  blue-gray,  impure  (argillaceous) 20 

3  Limestone,  alternating  beds  of  massive,  steely  gray,  arenaceous  limestone, 
weathering  brown  and  containing  corals,  and  fissile,  light-gray,  and  dense 
limestone ''O 

)  2    Limestone,  at   the  base   dark  blue-gray  and   very  compact,  changing   to  a 

browu-giay  arenaceous  limestone.     Dip  15°,  N.  10°  W 10 

)  1    Limestone,  light  drab,  finely  crystalline  and  dense,  somewhat  cherty.     Chert 

light  and  dark  gray ;  thickly  bedded. 

The  dip  of  the  lower  beds  of  the  section  is  15°.  Five  hundred  feet 
above  the  pass  it  is  18°,  and  near  the  summit  of  Bannock  Peak  it  is  10°. 
The  direction  of  the  dip  also  changes  from  N.  11°  W.  to  NW.,  becoming 
N.  41°  W.  on  the  summit.  The  beds  appeared  to  be  perfectly  conformable 
throughout. 


GALLATIN  VALLEY.  27 

It  will  be  observed  that  the  thicknesses  given  in  the  foregoing  section  to 
the  beds  niindx'red  16  to  10  inclusive  differ  considenibly  from  those  of  the 
Crowfoot  Ridge  section  The  correlation  of  the  beds  seems  to  be  correct; 
the  error  can  not  ])e  large  either  in  this  or  in  the  estimates  of  thicknesses, 
as  the  white  Quadrant  sandstones  above  and  the  arenaceous  Jefferson  lime- 
stones form  a  check  on  the  work.  This  difference  amounts  to  nearly  400 
feet  and  is  believed  to  occur  in  the  upper  beds  of  the  Madison  limestones. 

West  of  Quadrant  Mountain  and  Bannock  Peak  the  range  consists  of 
a  rugged  region  drained  by  the  Gallatin  River.  This  stream,  which  heads 
in  Gallatin  Lake  at  the  base  of  Three  River  Peak,  flows  through  a  valley 
that  is  one  of  the  most  beautiful  parts  of  the  park.  Broad  open  meadows, 
diversified  with  clusters  of  pines  and  spruces,  alternate  with  small  patches 
of  forest  that  cover  the  broad  valley  bottom.  To  the  south  the  slopes  rise 
steeply  to  the  peaks  of  Crowfoot  Ridge,  while  bold  cliffs  of  white  limestone 
wall  in  the  valley  upon  the  north.  The  river  flows  rapidly,  in  a  succession 
of  rapids  and  clear  pebbly  reaches,  cutting  the  heavily  bedded  limestones 
that  form  the  valley  floor. 

CROWFOOT  RIDGE  AND   GALLATIN   VALLEY. 

On  the  west  side  of  the  ridge  along  which  the  chief  stratigraphic  section 
was  studied  a  branch  of  Grayling  Creek  has  cut  a  deep  gulch,  trending 
toward  the  northwest.  This  follows  the  outcrop  of  the  Flathead  shales, 
and  has  the  gneiss  and  steeply  dipping  basal  sandstone  on  the  south  side 
and  the  massive  Paleozoic  Ihnestones  on  the  north.  About  a  mile  down  the 
gulch  a  fault  crosses  the  country  in  a  direction  east  of  north,  letting  down 
the  block  of  sedimentary  rocks  and  crystalline  schists  on  the  west  side  of 
the  fault,  so  that  the  strata  dip  at  a  more  uniform  inclination  of  15°  to  20°, 
and  also  30°,  NE.  This  throws  the  basal  quartzite  at  least  800  feet  lower 
down  than  the  west  end  of  the  crest  of  Crowfoot  Ridge,  and  brings  the 
Quadrant  quartzite  back  to  the  summit  of  the  west  spur  of  Crowfoot  Ridge, 
from  which  it  extends  down  its  northern  slope. 

At  the  western  base  of  the  end  of  this  mountain  ridge  the  sedimentary 
rocks  are  lost  sight  of  beneath  a  deep  accumulation  of  glacial  drift,  which 
obscures  the  contact  between  these  rocks  and  the  rhyolite  lava  that  has 
buried  them  and  the  underlying  crystalline  schists,  as  already  pointed  out. 
The  north  and  south  ends  of  the  fault  just  noticed  are  lost  beneath  the 
same  drift. 


28  GEOLOGY  OF  THE  YELLOWSTOJTE  NATIONAL  PARK. 

East  of  the  high  ridge  along  which  the  sedimentary  section  was  made, 
abeady  referred  to  as  Crowfoot  Ridge,  the  strata  are  folded  and  faulted  in 
a  pronounced,  though  not  an  extreme,  manner.  In  the  short  spur  between 
the  two  branches  of  the  drainage  east  of  the  ridge  there  is  a  marked  bend 
in  the  beds  of  limestone,  which  in  the  higher  part  of  the  spur  di))  steeply 
and  can  be  traced  continuously  into  the  main  body  of  the  ridge,  but  at  the 
lower  end  of  the  spur  are  nearly  horizontal.  There  is  thus  a  short  fault 
line  west  of  the  spur,  which  runs  out  in  the  head  of  the  gulch,  and  probably 
joins  a  longer  fault  which  terminates  somewhere  near  the  junction  of  this 
drainage  with  the  Gallatin  River,  as  shown  on  the  map  There  is  also 
evidence  of  horizontal  thrust  in  the  telescoping  of  the  limestone  layers, 
which  is  seen  on  the  east  escarpment  of  the  ridge. 

The  next  spur  east  of  the  one  called  Section  Ridge  is  a  long  low  ridge, 
formed  of  nearly  horizontal  beds,  with  a  slight  syncline  across  its  middle, 
the  axis  of  the  syncline  being  about  northwest  and  southeast.  At  its  south- 
ern end  the  beds  turn  up  abruptly  against  the  gneiss  ridge,  and  the  shaly 
horizons  are  eroded  down,  and  do  not  rise  in  a  high  spur  as  erroneously 
drawn  on  the  general  map.  Tliere  is  a  fold  or  bend  in  the  strata  as  they 
come  from  Section  Ridge,  the  beds  curving  down  towai'd  the  east  so  as  to 
permit  the  strata  in  the  low  spur  to  lie  at  a  low  angle.  This  is  probably 
accompanied  hj  slight  faulting,  with  north-south  trend,  situated  near  the 
bottom  of  the  drainage.     It  was  not  obseiwed,  however,  in  the  field. 

Between  this  spur  and  the  next  large  spur,  about  a  mile  east,  there  is  a 
broad  fold  in  the  strata.  The  beds  that  dip  at  a  low  angle  of  about  20°  to 
the  noi'th  and  northeast,  arch  over  to  an  abrupt  pitch  with  steep  angle  at  the 
east  side,  near  the  south  end  of  the  east  spur.  This  general  arch  is  compli- 
cated by  minor  folds,  not  indicated  on  the  map.  The  changes  in  dip  and 
the  differences  in  hardness  of  the  shales  and  limestones  show  themselves  in 
the  topography,  which  is  modified  by  glaciation.  The  easier  degradation 
of  the  shaly  layers  leads  to  sink  holes  beneath  stronger  limestone  layers. 
One  has  been  made  in  the  lowest  micaceous  shale,  with  the  first  massive 
limestone  layers  to  the  north.  Farther  east  a  small  rock  -bound  glacial  lake 
occurs  on  the  gneiss  at  its  contact  with  basal  quartzite.  North  and  north- 
east of  this  lake  the  lowest  belt  of  Cambrian  limestone  forms  a  bench  and 
a  long  slope  down  to  the  drainage,  which  flows  west  of  north.  Here  the 
general  dip  of  the  strata  is  30°  NE.  Near  the  lower  end  of  the  slope  just 
mentioned  are  four  small  folds  of  the  strata,  with  axes  trending  about 


UALLATIN  VALLF.Y.  29 

N.  10°  W.  The  upper  part  of  tliis  drainage  is  located  on  the  upper  shale 
belt  in  the  Cambrian,  l)nt  leaves  it  lower  down  the  slope.  The  upper  shale 
belt  may  be  traced  across  country  by  its  influence  on  the  topography,  form- 
ing saddles  where  it  crosses  spurs  which  trend  north,  and  giving  rise  to 
lateral  drainage  channels,  feeding  larger  ones  running  north,  or  forming 
basin-like  depressions  with  sink  holes,  as  already  noted. 

The  head  of  the  gulch  cut  in  the  shale  belt  just  mentioned  is  not  shown 
on  the  map,  but  it  is  (|uite  strongly  marked,  being  narrow  and  deep  and  trend- 
ing north,  and  receiving  the  drainage  of  the  small  pond  southeast  of  the  larger 
lake  noted  above.  The  west  wall  of  this  gulch  is  formed  of  the  lowest 
belt  of  Flathead  limestone,  with  the  lower  micaceous  shales  of  the  Flathead 
formation  to  the  west.  At  the  spot  where  the  drainage  from  the  small  j^ond 
falls  into  the  deep  gulch,  these  strata  are  inverted,  dipping  60°  or  70°  W. ; 
strike,  north  and  south.  Hence  the  lower  beds  appear  to  overlie  the  upper 
ones.  The  gneiss  is  only  a  short  distance  west.  The  inverted  beds  can  be 
traced  northward  into  vertical  beds,  and  then  into  others  dipping  toward 
the  northeast.  To  the  south  the  inverted  beds  continue  in  the  same  position 
until  they  abut  against  the  gneiss.  It  is  evident  that  there  has  been  some 
faulting  and  displacement  of  the  basal  formations  for  a  short  distance  in  the 
neighborhood  of  the  unconformity  just  mentioned. 

The  portion  of  the  high  ridge  east  of  the  shale  gulch  and  the  ponds 
previously  mentioned  is  in  general  a  syncline  with  a  flat  anticlinal  fold  at 
its  northern  end,  which  is  south  of  the  saddle  crossed  by  the  fault  to  be 
described.  The  dip  of  the  strata,  which  are  very  steep  near  the  gneiss, 
changes  from  almost  45°  NE.  to  15°  farther  north,  flattening  to  the  syncline 
already  mentioned.  The  axis  of  the  synclinal  fold  is  somewhat  west  of 
north,  and  the  same  fold  may  be  observed  to  the  southeast  of  this  ridge. 
Southeast  of  the  southern  end  of  the  ridge  a  drainage  channel  follows  the 
line  of  the  upper  shale  belt  in  a  southeast  dkection.  The  southern  side  of 
this  drainasre  is  formed  of  the  lowest  massive  belt  of  limestone,  and  south  of 
this  parallel  gulches  have  been  worn  in  the  lower  shale  belts.  These  drain 
either  through  cuts  across  the  belt  of  massive  limestone  or  in  sink  holes 
beneath  it.  Here  again  the  strata  are  inverted,  with  a  dip  of  50°  to  80° 
SW.,  changing  in  places  to  vertical  and  also  to  steep  dips  to  the  northeast. 
Near  where  the  gneiss  ridge  is  faulted  by  the  north-south  fault,  the  basal 
beds  of  the  sedimentary  series  are  inverted,  with  dip  of  20°  to  50°  SW., 


30      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

and  form  a  narrow  wedge  between  this  fault  and  the  gneiss.  The  Gallatin 
fault,  which  crosses  the  west  base  of  Three  River  Peak,  trends  in  a  north- 
northwest  direction,  crossing  Crowfoot  Ridge  three-quarters  of  a  mile  west 
of  Three  River  Peak,  and  crossing  the  ridge  north  of  it  at  the  saddle  one 
mile  north  of  the  gneiss,  thence  following  down  the  drainage,  to  die  out 
where  it  joins  the  short  fault  east  of  Section  Ridge.  The  trend  of  the  fault 
is  nearly  jjarallel  with  that  of  the  Gallatin  River,  as  will  be  seen  on  the  map. 
The  maximum  displacement  is  about  2,000  feet. 

The  long,  low,  flat-topped  ridge  lying  between  this  fault  and  Gallatin 
River  consists  of  nearh'  horizontal  beds  of  Carboniferous  limestone  capped 
by  the  white  Quadrant  quartzite  or  sandstone  occun-ing  at  the  top  of  the 
Carboniferous  series.  The  dip  of  the  beds  is  about  5°  NE.  From  this  it 
is  evident  that  there  must  be  a  fault  or  a  fold  between  this  ridge  and  the 
higher  one  east  of  Gallatin  River.  A  fold  exists  west  of  Bighorn  Pass,  but 
it  was  not  followed  down  the  valley.  On  both  sides  of  the  low  ridge  west 
of  Gallatin  River  are  bodies  of  intrusive  igneous  rock,  related  to  the  dacite- 
porphyry  of  the  Holmes  bysmalith  in  composition  and  petrographical 
character.  The  rock  is  lithoidal  and  holds  small  mica  phenocrysts;  it  is 
fissile  near  the  contact  with  sedimentary  rocks,  and  mas.sive  a  few  feet  dis- 
tant. It  crosses  the  fault  line  and  is  found  on  its  western  side  intnided  in 
the  axis  of  an  anticlinal  fold  in  Cambrian  rocks.  Its  intrusion  followed  or 
accompanied  the  faulting.  On  the  eastern  side  of  the  flat  ridge  it  apjjears 
as  an  intrusive  sheet,  about  50  feet  thick,  forced  between  beds  of  Carbonif- 
erous limestone.  This  exceptional  occurrence  of  igneous  rock  as  an  intru- 
sive sheet  in  massive  Carboniferous  limestone  is  of  limited  extent  and  is  in 
the  immediate  neighborhood  of  a  fault,  with  which  it  is  dii-ectly  connected. 
Similar  rock  has  been  intruded  into  the  west  base  of  Three  River  Peak,  and 
it  may  be  assumed  that  the  Holmes  bysmalith  was  connected  with  the  same 
line  of  faulting.  The  intrusion  of  this  mass  has  been  shown  to  have  been 
subsequent  to  the  upheaval  that  permitted  the  intrusion  of  the  Indian  Creek 
laccolith;  hence  it  follows  that  the  more  steeply  upturned  position  of  the 
ffneiss  and  Cambrian  strata  west  of  this  fault  was  due  to  a  later  movement 
than  the  general  uplifting  of  the  body  of  the  range.  This  steeper  uplift  was 
limited  on  the  east  b}^  the  fault  last  mentioned,  and  by  that  cutting  across 
the  northwest  end  of  Crowfoot  Ridge,  which  faults  are  probably  contempo- 
raneous and  were  accompanied  by  a  slight  faulting  east  of  Section  Ridge. 


THE  GALLATIN  MOUNTAINS.  31 

QUADRANT  MOUNTAIN,  BANNOCK  PEAK,  AND  THE   VALLEY  OF   THE 

GALLATIN  KIVER. 

In  the  less  disturbed  eastern  portion  of  the  GaHatin  Range  the  Cam- 
brian and  Devonian  strata  pass  northward  with  a  low  northeasterly  dij),  dis- 
appearing beneath  the  more  massive  beds  of  Carboniferous  limestone  alone- 
the  base  of  the  mountains  north  of  Panther  Creek.  The  bold  southern 
escarpments  of  Quadrant  Mountain  and  Bannock  Peak  exhibit  almost  the 
entire  section  of  Carboniferous  strata,  since  they  are  topped  near  the  summit 
of  the  former  mountain  by  Juratrias  beds.  The  nearly  horizontal  beds  form 
massive  cliffs  that  extend  with  gentle  inclination  along  the  eastern  escarp- 
ment of  this  mountain,  in  lines  parallel  to  the  slope  of  its  plateau-like  top, 
and  that  sink  beneath  the  level  of  the  valley  as  Fawn  Creek  is  approached. 
They  may  be  plainly  made  out  in  Mr.  Holmes's  panoramic  sketch  of  the 
Gallatin  Range,  PI.  IV.  Their  character  in  Bannock  Peak  is  seen  in  PI.  VIII. 
From  here  they  extend  westward  along  both  sides  and  the  bottom  of  the 
valley  of  the  Gallatin  River,  forming  the  cliff  along  its  northern  side  and 
dipping  at  a  low  angle  toward  the  southeast,  while  on  the  south  they  form 
a  high  ridge  and  the  mountainous  spur  of  Crowfoot  Ridge. 

BANNOCK  PEAK. 

Bannock  Peak  is  a  sharp  mountain  summit  north  of  the  head  of  Panther 
Creek.  Resting  upon  the  more  readily  eroded  beds  of  the  Silurian  and 
Devonian  terranes,  the  massive  Madison  limestones  form  the  main  mass  of 
the  mountain  and  are  capped  by  the  resistant  beds  of  the  Quadrant  quartzite, 
whose  white  ledges  form  a  bold  escai-pment  that  encircles  the  peak. 

On  the  northern  side  of  the  mountain  a  section  was  made  of  the  strata 
exposed  in  the  wall  of  the  amphitheater  cut  between  this  peak  and  the  broad 
plateau  summit  of  Quadrant  Mountain.  This  amphitheater,  though  appar- 
ently open,  as  shown  on  the  map,  is  divided  by  a  spur  pi'ojecting  southward 
from  the  extreme  western  end  of  Quadrant  Mountain.  This  section  was 
made  from  the  bed  of  Panther  Creek  up  the  center  of  the  amphitheater  to 
the  crest  of  the  ridge  dividing  this  from  the  amphitheater  at  the  head  of 
Fawn  Creek.  The  beds  are  exposed  in  a  series  of  steps  or  benches,  the 
lowest  strata  being  the  arenaceous  Jefferson  Hmestones,  the  underlying  beds 
being  covered  by  drift. 

The  beds  dip  N.  21°  W.  at  8°,  the  determination  being  made  on  No.  4 
of  the  section 


32 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


Crowfoot  Num- 
sectioD .      ber. 

(o)     33  23 

f22 

21 


32  < 


31, 


20 


as 

30a, 6  12 
29  11 


28  10 


28   9 
28   8 


2 
26   1 


Bannock  Peak  section.  „  , 

Feet. 

White  beds,  sandstones  and  quartzites  with  interbedded  limestone 325 

Limestone,  drab,  finely  crystalline,  hard,  forms  knoll  of  saddle 100 

Limestone,  dense,  well  bedded,  very  light  gray-brown,  compact,  weathered 

surface,  very  finely  granular 30 

Limestone,  forming  great  ledge  of  amphitheater  saddle.  At  the  base  this 
limestone  is  brecciated,  being  a  gray  limestone  with  brown  and  blue  frag- 
ments. The  limestone  is  generally  splintered,  the  lower  two-thirds  well 
brecciated  and  splintered  and  weathering  in  pinnacles,  recesses,  etc.  This 
weathering  is  further  facilitated  by  the  occurrence  of  great  seams  of  caloite, 
4  inches  thick,  and  pockets  of  the  same  material.     In  general  the  rock  is 

finely  crystalline,  gray,  weathering  gray-brown 200 

Limestone  breccia 10 

Limestone,  light  gray-brown 15 

Limestone,  very  linely  crystalline,  splintery,  dense,  light  gray 15 

Limestone,  finely  crystalline,  brown,  weathering  same  color 20 

Limestone,  finely  crystalline,  very  light  brown,  well  bedded  and  banded.     No 

fossils  seen 30 

Limestone,  coarsely  crystalline,  massively  bedded,  splintery,  brownish,  weath- 
ering gray-brown ;  is  fossiliferous,  and  forms  a  ledge 50 

Interval 125 

Limestone,  coarsely  crystalline,  brown-gray,  weathering  a  lighter  tint.  Con- 
tains fossils 50 

Limestone,  white  or  very  light  gray,  crystalline,  compact,  massive,  not 
splintered;  with  small  scattered  calcite  crystals,  weathered  surface,  finely 
granular.     The  upper  beds  are  more  coarcely  crystalline  and  sometimes 

indurated 165 

Limestone,  brown,  banded  with  darker  fossiliferous  layers,  the  rest  denser; 
weathers  with  buff  granular  surface,  often  pink  or  light  red.     Breaks  into 

fragments  2  to  8  inches  across 30 

Limestone,  brown,  fissile,  contains  fossils 6 

Limestone,  dense,  blue-gray  mottled  with  buff-brown,  with  occasional  thin 

layers  of  coarsely  crystalline  limestone 100 

Limestone,  fissile,  purple-red,  fossiliferous,  and  resembles  the  limestone  of  the 

saddle  of  Antler  Peak 5 

Limestone,  brecciated,  fragments  sparsely  scattered,  fossils  abundant 5 

Limestone,  crystalline,  gray,  crumbly,  containing  fossils,  weathers  gray  and 
exposes  fossils  and  crinoid  stems.  Beds  2  to  6  feet  thick,  and  strike  jointed. 
Becomes  darker  and  more  finely  crystalline  near  top.     Strike,  S.  70°  W. ; 

dip,8°N 80 

Limestone,  cherty,  crystalline,  gray-brown,  weathers  light  with  finely  granular 

surface,  sometimes  pinkish,  the  chert  weathering  a  rust  color 25 

Limestone,  crystalline,  cherty,  gray,  thinly  bedded  (2  to  6  inches) ;  few  crinoid 
stems;  blue  chert;  fossils  more  abundant  in  upper  layers.     Slope  of  beds, 

70  NW 125 

Interval,  probably  a  blue  limestone,  crystalline,  dense 50 

Limestone,  crystalline,  light  gray  and  gray,  very  arenaceous,  somewhat 
granular,  with  rough,  pitted,  and  honeycombed  weathered  surface.  This 
bed  underlies  any  seen  in  the  east  face  of  Bannock  Peak 60 

a  Quadrant  quartzite. 


THE  GALLATIN  MOUNTAINS.  33 

QUADRANT   MOUNTAIN. 

The  broad  sumrnit  of  Quadrant  Mountain  is  an  open  and  grass-covered 
area,  above  wliicli  a  bold  pyramid  formed  of  the  red  Teton  sandstones 
rises  quite  abruptly.  Snow  fields  cover  the  summit  in  early  spring  and 
remain  through  the  summer,  nourishing  streams  that  flow  in  cascades  over 
the  walls  of  the  Pocket.  The  upper  slopes,  which  lie  beneath  the  cliffs  of 
white  Quadrant  sandstones,  are  dark  with  the  lichen-covered  debris  from 
the  overhanging  walls,  while  the  slopes  beneath  are  thickly  timbered.  The 
sujnmit  of  the  mountain  slopes  northward  with  an  angle  of  3°  to  4°,  con- 
forming very  nearly  to  the  bed  of  the  rocks.  The  flatness  of  the  mountain 
top  is  clearly  due  to  the  resistant  natui'e  of  the  Teton  limestones,  as  the 
overlying  clays  and  sandstones  are  rapidly  removed  by  erosion.  This 
mountain  block  is  of  very  simple  stratigraphical  structure.  The  beds  are 
slightly  flexed,  without  faulting,  and  are  undisturbed  by  intrusives.  The 
beds  forming  it  are  the  Madison  limestones,  covered  by  the  white  Quadrant 
quartzites  overlain  by  the  cherty  beds  of  the  Teton  formation.  The  strata 
forming  the  mountain  are  clearly  a  continuation  of  those  of  Antler  Peak  and 
Panther  Creek  Canyon;  on  the  west  the  bods  are  seen  to  be  connected  with 
those  of  Bannock  Peak  through  the  saddle  of  the  amphitheater,  while  on  the 
north  the  Quadi-ant  quartzites  form  the  floor  of  Fawn  Creek  Valley  and 
pass  under  the  slopes  of  Little  Quadrant  Mountain.  Eastward  the  beds 
end  in  a  cliff  and  steep  slope  along  that  north-south  line  which  separates 
the  sedimentaries  of  the  range  from  the  lavas  of  the  plateau.  The  general 
dip  of  the  beds  is  a  little  west  of  north,  about  8°,  so  that  the  slope  of  the 
summit  corresponds  approximately  to  the  dip  of  the  beds. 

The  summit  of  the  mountain  has  been  carefully  examined.  West  of 
the  Pocket  the  cherty  Teton  limestone  covers  the  surface,  which,  when 
examined  closely,  is  seen  to  be  rough,  gullied,  and  hummocked.  The  red 
hill  on  the  summit  of  the  mountain,  southeast  of  the  Pocket,  is  composed  of 
the  red  Teton  sandstones.  This  point  is  about  200  feet  higher  than  the 
surrounding  summit.  On  the  east,  south,  west,  and  northwest  these  beds 
commence  at  the  very  foot  of  the  hill ;  on  the  northeast  the  area  extends  about 
one-fifth  of  a  mile  farther.  The  general  summit  from  the  red  jDoint  north 
is  formed  of  the  Teton  cherty  limestone  and  its  associated  lingula-bearing 
limestone,  down  to  9,200  feet,  where  the  red  beds  again  cover  a  portion  of 
PT  II 3 


34 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


the  mountain.  Eastward  the  cherty  beds  have  been  removed  from  the 
bench,  and  the  white  beds  of  Quadrant  quartzite  are  exposed. 

On  the  summit  of  the  9,100-foot  hill  a  small  outcrop  of  the  red  and 
yellow  sandstone  (No.  38  of  section  below)  is  exposed.  West  of  this  hill  is 
a  deep  cut,  into  which  the  small  drainages  of  this  part  of  the  summit  flow. 
The  surface  of  the  area  covered  by  the  red  beds  is  generally  smooth  and 
grassy;  the  shales  are  exposed  in  cuts,  but  appear  only  as  detritus  on  the 
summit. 

On  all  sides  of  the  mountain  the  white  beds  of  Quadrant  sandstone 
form  an  escarpment,  often  capped  by  the  cherty  limestone.  This  Teton 
cherty  limestone  varies  greatly  in  character.  Often  it  is  a  cherty  sandstone 
with  little  if  any  calcareous  material  in  it;  again  it  is  a  true  limestone;  and 
these  two  extremes  grade  into  each  other.  The  chert  seems  to  be  formed 
of  sand,  for  the  transition  between  the  sandstone  and  the  chert  is  often  very 
gradual.     The  color  is  a  grayish  brown. 


Crow- 
foot 
sec- 
tion. 

Nuni 
ber. 

-39 

38 

38 

37 

37 

36 

o 

1' 

36 
35 

35 
34 

34 

33 

32 
31 

30 
29 
28 
27 

T 

33 

26 

25 

24 

23 

22 
21 

20 

Section  of  beds  exposed  at  the  southeastern  end  of  Quadrant  Mountain. 


Feet. 

Sandstone,  red  and  orange  colored,  coarsely  granular,  weathers  in  blocks 15 

Calcareous  shale,  dark  slate  colored,  fossiliferons 5 

Limestone,  bright  yellow,  fissile,  with  platy  debris,  grading  into  yellow  and  red 

spotted  calcareous  sandstones  below 40 

Shales,  light  greenish  drab,  changing  to  red  and  grading  into  overlying  beds 75 

Conglomerate  of  red  and  gray  quartz  pebbles  in  limestone  matrix 10 

Cherty  sandstone,  the  lower  part  without  chert,  is  brown;  slightly  calcareous  at 

base,  becoming  more  so  above 100 

Limestone,  dense,  white,  weathering  same  color 10 

Sandstone  and  limestone  in  alternating  bands 15 

Limestone,  light  gray  and  dense  and  pure 12 

Quartzite,  pure  whi  te,  thin  bedded,  forms  a  persistent  band  along  face  of  mountain . .  6 

Quartzite,  more  thickly  bedded,  white 65 

Limestone,  very  light  gray,  somewhat  dense,  containing  very  small  fragments  of 

light-colored  chert 10 

Quartzite,  white,  calcareous,  with  intercalated  bands  of  limestone  carrying  quartzite 

fragments 30 

Limestone,  light  gray,  with  angular  fragments  of  sandstone 5 

Quartzite,  white,  weathering  pink  and  rust  color,  but  appearing  black  when  Been 

from  a  distance,  owing  to  the  growth  of  lichens  upon  it 130 

Limestone,  light  gray,  dense 2 

Sandstone,  well  banded,  white,  saccharoidal 6 

Sandstone,  very  calcareous,  saccharoidal,  white  and  rust  color 10 

Talus  slope  of  sandstone  blocks;  also  of  cherty  limestone 100 


QUAUKANT  MOUNTAIN. 


35 


Section  of  beds  exposed  at  the  xoutheastern  end  of  Quadrant  Mountain — Continued. 


Crow- 
foot 
nee- 
tlou. 


32 


Num- 
ber. 

19 


Feet. 


18 


17 


16 


15 

f  14 

13 


12 


U 


31 


29^    3 


30 


28 
28 


Liiiii'stoiio  breccia.  Tbo  lower  30  foet  ia  a  white  limestone,  weathering  cream,  cnn- 
taininj;  angular  fragments  of  bine,  brown,  and  buff  limestone,  from  one-eighth 
of  an  inch  to  2  inches  in  diameter.  The  matri.'i  is  coarsely  granular,  and  grades 
above  the  first  .30  feet  into  a  crnshed  and  splintered  limestone  similar  to  the 
iniitrix  Just  mentioned.  The  outcrop  is  massive,  rough  weathering,  often  pinkish. 
Kock  is  slightly  clierty.     Dip,  12^'  N. ;  strike,  S.  78'^  W 

Limestone,  finely  crystalline,  gray,  weathering  light  gray,  with  granular  surface. 
Generally  massive,  though  bedded  at  base.  No  fossils  seen;  is  splintery  and 
weathers  rough 

Limesti>ne,  very  light  brownish  gray,  splintered  and  cemented  by  calclte  in  strings, 
and  by  blue  limestone 

Limestone,  brecciated  at  the  base;  matrix  gray,  fragments  angular,  brown  and 
brownish  gray ;  above  this  the  limestone  is  massive  and  gray.  Seamed  with  cal- 
cite  and  carries  much  of  that  mineral  in  pockets.  It  is  somewhat  cherty  at  the 
base 

Interval;  no  exposure 

Limestone,  finely  crystalline  and  granular,  brown,  somewhat  cherty 

Limestone,  very  fine  grained  with  spai'sely  disseminated  chert,  but  varying  to  a 
very  coarse-grained  blue-gray  rock.  Color  in  general  a  light  brown-gray. 
Weathers  into  irregular  warped  plates,  due  to  jointing 

Limestone,  coarsely  crystalline,  brownish  gray,  weathering  gray  with  granular 
surface.     Irregularly  bedded ;  fossiliferous;  much  broken  by  vertical  jointing. .. 

Limestone,  finely  crystalline,  generally  thinly  bedded,  sometimes  dark  gray,  but 
mostly  brown,  with  granular  weathered  surface,  or  a  blue-gray  more  coarsely 

crystalline  limestone.     Dip,  5°  N 

10b  Limestone,  similar  to  No.  10a,  but  well  banded.  The  fossilii'erovis  layers  weather- 
ing blue-gray ;   the   nonfossiliferous   bands    denser,  granular,   weatheriug  light 

brown ,  and  1  to  3  inches  thick 

lOo  Limestone,  in  alternating  layers  of  light  gray,  finely  crystalline  and  darker,  coarsely 
crystalline  and  fossiliferous.     Dip,  4°  NW .1. 

Interval ;  no  exposure 

Limestone,  finely  granular,  light  brown,  weathering  same  color;  fissile,  contains 
remains  of  fossils.     Talus  indicates  a  greater  thickness  than  that  given 

Interval;  no  exposure 

Limestone,  light  gray,  finely  crystalline,  with  gray  and  granular,  glistening,  weath- 
ered surface 

Interval;  no  exposure 

Limestone,  coarsely  crystalline,  dark  gray,  weathering  the  same  color;  fossiliferous 
fragments 

Limestone,  forming  a  well-marked  and  prominent  ledge  extending  around  the 
mountain;   massive,  light  drab,  weathering  dark  gray  and  brown  with  glossy 

beaded  crust.     Contains  corals  and  other  fossils 

2    Interval ;  no  exposure 

1  Limestone,  cherty,  crystalline  but  not  granular,  compact,  massively  bedded.  The 
upper  part  fossiliferous,  containing  crinoid  stems,  corals,  and  spirifers.  Dip, 
about  5° N 


135 


65 


35 


50 
80 
10 


75 


25 


90 


10 

25 
25 

5 
10 

12 
65 

15 


45 
60 


60 


36  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

lilTTLE  QUADRANT  MOUNTAIN  AND  FAWN  CREEK  YALIiEY. 

LITTLE  QUADRANT  MOUNTAIN. 

Nortli  of  Quadrant  Mountain  is  another  flat-topped  elevation,  known  as 
Little  Quadrant  Mountain,  wliich  is  clearly  defined  from  tlie  adjacent  moun- 
tains by  the  deeply  incised  valleys  of  Fawn  Creek  and  the  headwaters  of  the 
Gardiner.  The  mountain  is  carved  out  of  a  block  of  Mesozoic  strata,  into 
wliich  numerous  sheets  of  andesite-porphyry,  offshoots  from  the  Gray  Peak 
intrusion,  have  been  injected.  The  resistant  nature  of  these  intruded  sheets 
has  produced  the  marked  terracing  which  now  forms  so  characteristic  a 
feature  of  the  southern  slopes.  The  following  section,  made  by  Mr. 
Geoi'ge  M.  Wright,  represents  the  beds  exposed  on  the  southern  side  of 
the  mountain,  the  lowest  strata  being  the  brecciated  limestone  forming  the 
top  of  the  Madison  limestone  series,  through  wliich  Fawn  Creek  has  cut  a 
small  canyon  at  the  forks  of  the  stream: 

Section  of  beds  exposed  on  south  side  of  Little  Quadrant  Mountain. 

Kum- 
ber.  Feet. 

4  Sandstone 20 

Interval  with  no  exposure  (broad  bench  about  300  yards  wide) 75 

Mica-hornblende-andesite-porphyry 50 

3  Cherty,  arenaceous,  and  calcareous  beds : 

Limestone 2 

Interval  with  no  exposure 35 

Cherty,  arenaceous,  and  calcareous  beds 40 


Teton 
limestone. 


77 


Quadrant 
quartzite. 


2  Sandstone  and  limestone : 

(6)  Limestone,  white,  much  of  it  brecciated  and   mixed   up  with 

sandstone 20  or  25 

(o)  Sandstone 175 


200 

Interval  with  no  exposure r-       100 

Madison   (  1  Brecciated  limestone,  having  some  layers  compact,  not  brecciated;  in  walls  of 
limestone,  i  miniature  canyon  at  junction  of  branches  of  Fawn  Creek 40 

The  total  thickness  of  this  section  is  not  given,  owing  to  the  uncer- 
tainty of  the  exact  thickness  of  two  of  the  intervals  above  mentioned. 

Above  the  beds  of  the  section  just  noted  there  is  a  long  steep  slope, 
rising  300  feet  or  more  to  a  prominent  cliff  formed  of  the  Ellis  sandstones. 


LITTLE  QUADRANT  MOUNTAIN. 


37 


Another  section,  made  by  Mr.  Wrij^ht,  sliows  the  sequence  and  thickness  of 
the  beds  from  this  liorizon  to  the  summit  of  the  mountain. 

Section  of  beds  exposed  on  south  side  of  Little  Quadrant  Mountain. 


Num- 
ber. 


Feet. 


Colorado . 


* 


Mica-horDblende-porpbyry 125+ 


Dakota 


Ellis 

sandstoDe.  | 

I 


Ellis 
limestone. 


I  11  Carbonaceous  sbalos. 

Interval  with  no  exposure 100  or  150 

10  Sandstone. 

Interval  with  no  exposure .50 

Additional  interval  with  no  exposure 175 

Mica-hornblende-porphyiy  several  feet  thick,  with  sandstone  in  small  exposures 
below  it  in  slope  showing  no  other  exposures.     Number  of  feet  given  is  height 

of  slope 100 

9  Sandstone  and   conglomerate.      These   are  here   overlain  by  the   mica-horn- 
blende-andesite.     The  sectiou  was  again  continued  at  a  place  about  100  yards 

southeast  from  the  last-menC  med  exposure 25 

Interval  with  no  exposure 340 

8  Soft  gray  and  drab  beds,  weathering  into  light-green  shales 10 

7  Calcareous  sandstoue  and  limestone 50 

Interval  with  no  exposure 75 

6  Oolitic  limestone 2 

I  Fossiliferous  shales,  occurring  as  follows: 

Shalef,  gray,  soft 15 

Interval  with  uo  exposure 60 

Shales,  gray,  clayey,  in  cut  of  stream  flowing  from  pass  at  west  end  of 

Little  Quadrant Few. 

Limestone 30 

At  the  west  end  of  Little  Quadrant  Mountain  a  branch  of  Fawn  Creek 
has  cut  back  to  a  low  divide  separating  this  mountain  from  Gray  Peak. 
The  lowest  beds  exposed  by  this  stream  are  the  Ellis  limestones,  which  are 
exposed  in  the  gulch  25  feet  deep  near  the  forks  of  the  stream.  The  beds 
dip  N.  25°  W.  at  10°.  The  strata  contain  numerous  fossils  and  are  quite 
like  the  beds  described  later  in  the  Fan  Creek  section.  In  the  stream 
channel  above,  there  is  an  exposure  of  very  fissile  calcareous  sandstone  in 
a  ledge  5  feet  thick,  which  is  overlain  by  very  arenaceous,  granular,  cross- 
bedded,  gray  limestone,  containing  fossils  which  are  mostly  comminuted 
and  broken.  This  exposure  is  20  feet  thick,  and  the  bed  is  overlain  by  a 
sandstone  containing  a  few  scattered  pebbles.  The  strike  is  S.  35°  W.,  and 
the  dip  is  10°  NW.  Above  this  the  stream  flows  over  a  small  exposure 
of  Dakota  conglomerate,  which  is  overlain  by  andesite-porphyry,  forming  a 
cliff  75  feet  high,  over  which  the  stream  flows  in  a  succession  of  cascades 
This  rock,  which  is  an  extension  of  the  Gray  Peak  intrusion,  is  hornblendic, 


38 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


generally  much  decomposed,  and  shows  no  megascopic  mica.  This  por- 
phyry forms  a  bench  north  of  the  stream  which  extends  back  to  the  base  of 
the  cliffs  where  Dakota  conglomerates  occur.  In  the  stream  channel  a 
brownish-gray  sandstone  speckled  with  black,  and  belonging  to  the  Dakota 
series,  is  overlain  to  the  east  by  the  andesite-porphyry,  forming  the  two 
9,000-foot  hills  shown  on  the  map.  These  higher  beds,  forming  the  west 
end  of  Little  Quadrant,  are  tilted  up  by  the  porphyry  intrusion.  The 
following  section,  made  by  Mr.  Wright,  shows  the  sequence  and  thickness 
of  the  beds  exposed  in  ascending  the  creek,  the  beds  being  given  in  descend- 
ing order.  The  thicknesses  are  estimated  and  approximate,  and  are  given 
in  feet: 


Num- 
ber. 


Section  on  north  side  of  head  of  Faion  Greek  Valley. 


Feot. 


Dakota  ... 


Ellis 
Bauds  tone. 

Ellis 
limestone. 

Teton 
limestone. 
Quadrant 
quartzite. 


50 

50+ 

50 


{Mica-hornbleude  porphyry  ..."| 

Limestone > 300 
Mica-hornblende-porphyry  ...J 

7     Sandstone 

6    Conglomerate 

^  Interval  with  no  exposure 

^)  Sandstone Few. 

Hornblende-porpliyry,  in  sloping  belt  across  an  interval 165 

4     Sandstone,  very  calcareous 15 

3    Limestone,  very  arenaceous 25 

Interval  with  no  exposure— steep  slope 365 

Mica-hornbleuile-porphyry 40+ 

Interval  with  no  exposure 100 

2    Cherty,  arenaceous,  and  calcareous  beds 35+ 

Interval  with  no  exposure 100 

1     Sandstone  in  bed  of  Fawn  Creek. 

Total  thickness  of  section 1,  295+ 

Total  thickness  (approximate)  of  intruded  porphyry 505 

Total  thickness  of  sedimentary  rocks  and  intervals 790 

The  slopes  on  the  northern  side  of  the  west  end  of  the  mountain  show 
a  succession  of  beds  very  similar  to  that  of  the  section  just  given.  The  meas- 
urement made  of  the  series  from  the  Dakota  conglomerate  to  the  summit 
of  the  ridge  showed  the  100  feet  of  conglomerate  and  sandstone,  which 
was  assigned  to  the  Dakota,  overlain  by  45  feet  of  compact  gray  limestone 
considerably  altered  by  intrusive  sheets  of  porphyry,  which  occur  both 
above  and  below  the  bed  and  also  spKt  it  in  half.  The  overlying  sand- 
stone, which  forms  the  summit  of  the  Dakota  series,  is  a  pure  white,  rather 


FAWN  CltEKK  VALLEY.  39 

soft  and  fine-grained,  massive  bed,  whose  outcrops  often  weather  a  light- 
brown.  The  thickness  is  50  feet,  and  it  is  overhiin  by  carbonaceous  shales 
which  are  (juite  arenacetms  at  tho  base  and  become  more  argillaceous  above. 
These  beds  form  the  cliffs  extending  eastward  around  the  sides  of  the 
crescent-like  amphitheater  cut  in  the  northwestern  wall  of  the  mountain. 
The  black  shales  extend  eastward  along  the  crests  of  the  cliffs  of  the 
crescent  ann)hitheater  for  nearly  a  mile,  when  they  break  down  and  the 
sandstone  forms  the  summit  of  the  cliff.  In  the  northwestern  slopes  of 
the  mountain,  sandstone  is  exposed  in  nearly  all  the  lateral  gullies  and 
stream  channels,  the  upper  sandstone  bed  of  the  Dakota  being  especially 
prominent  and  forming  a  persistent  ledge  that  extends  ai'ound  the  north 
spur  of  the  mountain  and  constitutes  the  wall  of  the  amphitheater  cut  iu 
its  eastern  face.  Beneath  the  cliffs  which  form  the  wall  of  the  northwestern 
part  of  the  mountain  an  andesite-porphyry  sheet  has  furnished  the  material 
for  a  great  morainal  accumulation  of  ang-ular  rocks,  concealing  all  expos- 
ures and  rendering  travel  difficult.  The  persistent  nature  of  these  andesite- 
porphyry  sheets  is  shown  by  their  occurrence  iu  so  many  localities  at 
the  same  stratigraphic  horizon.  In  the  stream  channel  noi'th  of  Little 
Quadrant  the  sheet  of  andesite-porphyry  occurring  between  the  Dakota 
limestone  and  the  conglomerate  is  well  exposed  at  9,000  feet.  In  the 
vicinity  of  the  lakes  at  the  head  of  the  valley  the  porphyry  forms  low 
rounded  knolls,  whose  surfaces  are  scored  and  polished  by  glacial  action. 
The  lower  slopes  east  of  Little  Quadrant  have  been  carefully  examined, 
but  the  morainal  drift  obscures  all  outcrops. 

FAWN    CREEK    VALLEY. 

The  valley  of  Fawn  Creek  shows  good  exposures  of  the  Carboniferous 
rocks,  overlain  by  the  softer  Mesozoic  series.  In  a  little  gulch  near  the 
forking  of  the  creek,  the  Quadrant  quartzite  series  is  well  exposed.  On 
the  south  fork  of  the  stream,  just  above  this  junction,  a  green  magnesian 
bed,  whose  surface  is  red  from  the  wash  of  the  weathered  outcrop,  is  also 
exposed.  The  overlying  bed  is  a  dark  pm-plish-red  rock  spotted  with 
green,  highly  ferruginous  and  argillaceous,  being  a  very  impure  dolomite. 
This  rock  is  overlain  b}^  an  outcrop  of  brecciated  limestone,  which  is 
believed  to  repi'esent  the  highest  bed  of  the  Madison  limestone  series. 
This  brecciated  character  and  the    granular  weathered  surface  of  these 


40      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

limestones  are  persistent  features  of  the  upper  beds  of  the  IMadison  series 
in  this  vicinity.  These  beds  are  overlain  by  the  white  Quadrant  quartzites, 
which  are  well  exposed  in  the  stream  channel.  In  the  bottom  of  the  amphi- 
theater at  the  head  of  Fawn  Creek,  a  coarsely  crystalline  brown  Hmestone 
is  well  exposed.  The  rock  is  fossiliferous,  but  the  fauna  presents  no  features 
different  from  those  of  the  underlying  limestones.  The  beds  dip  10°  N. 
The  amphitheater  floor  is  heaped  up  in  places  with  great  piles  of  debris, 
but  presents  many  smooth  exposures  of  a  dark,  slaty  limestone  and  of  the 
coarsely  crystalline  rock  just  mentioned.  In  the  latter  there  are  numerous 
large  sink  holes  or  "swallow"^  holes,  in  which  the  waters  flowing  from  the 
snow  banks  of  the  amphitheater  walls  pass  underground,  to  reappear  two 
miles  down  the  valley  as  a  large  stream  which  forms  the  headwaters  of 
Fawn  Creek.  The  section  of  beds  exposed  in  the  amphitheater  walls  to 
the  east  has  already  been  given  in  the  account  of  Quadrant  Mountain. 
Nowhere  is  the  character  of  the  Quadrant  quartzite  and  of  the  immediately 
underlying  Madison  limestones  better  shown  than  it  is  in  the  walls  south  of 
Fawn  Creek  Valley.  The  sections  which  have  already  been  given  show 
the  relative  thickness  of  these  beds  and  the  development  of  the  impure 
argillaceous  dolomites  whose  red  ledges  form  so  prominent  a  feature  of  the 
rock  outcrops. 

A  comparison  of  the  sections  of  the  Quadrant  quartzites  made  on  the 
walls  of  Quadrant  Mountain  is  given  in  the  following  table.  A  precise 
separation  of  the  sandstones  from  the  interbedded  limestones  is  not  always 
possible.  Many  of  the  sandstones  are  very  calcareous,  and  in  some  cases 
would  perhaps  be  classed  as  arenaceous  limestones. 

I  Handbook  of  Physical  Geology,  A..  J.  Jukes-Brown,  p.  87,  London,  1884. 


REGION  NOltTII  OF  (iALLATIN  RIVER. 
Com})ari8on  of  sections  of  Quadrant  formation. 


41 


"Pocket." 

Feet. 

"Amphitheater." 

Feet. 

"yiiailninl."  southeast 
corner. 

FePt. 

r,  q.  Sandstone 

15 

Sandstone   with   in- 

r.  Limestone 

10 

p.  Limestone 

6 

terhodded     1  i  m  e  - 

p,  (/.  Sandstones  .  ^ 

15 

5 

stone  

265 

0.  Limestones  .  S 

n.  Limestone 

15 

n.  Limestone 

12 

m.  Sandstone 

18 

k-m.  Qnartzite 

71 

1.  Limestone 

2 

j.  Limestone 

10 

k.  Sandstone,  etc . 

148 

/.  Limestone 

4 

i.  Limestone 

h.  Limestone 

30 
5 

209 

e.  Sandstone 

3 

f,f,9-  Qnartzite 

130 

272 

283 

d.  Limestone 

2 

d.  Limestone  .. .. 

2 

c.  Sandstone 

6 

c.  Sandstone 

6 

h.  Lime.stone 

10 

b.  Limestone 

10 

a.  Sandstone 

36 

a.  Talus 

100 

326 

401 

Madison  limestones  beneath  above  series. 

On  the  summit  of  the  ridge  west  of  Fawn  Creek  amphitheater,  the 
Teton  limestone  is  well  exposed,  the  dip  being  15°  and  the  direction 
N.  26°  W.  These  beds  are  undoubtedly  tilted  by  their  proximity  to  the 
Gray  Peak  bysmalith  mass,  although  the  tilting  is  not  uniform,  as  the  red 
sandstones  forming  the  hill  farther  north  have  a  dip  of  but  10°  in  the 
direction  N.  15°  W. 

REGION  NORTH  OF  GALLATIN  RIVER. 

As  already  pointed  out,  the  escarpment  wall  on  the  north  side  of 
Gallatin  River  consists  of  massive  Madison  limestones  topped  by  the  white 
sandstone  or  qnartzite  of  the  Quadrant  formation.  These  beds  dip  at  an 
angle  of  about  10°  NE.  throughout  the  greater  part  of  the  distance,  having 
a  more  northerly  dip  in  the  vicinity  of  Bannock  Peak,  and  at  the  western  end 
of  their  exposure  curving  over  from  a  northeasterly  to  a  northwesterly  dip 
of  5°  to  10°,  bending  down  toward  the  profound  fault  plane  that  bounds 
them  on  the  west  and  brings  them  against  subaerial  breccias  of  andesite. 
Within  the  limits  of  this  low  anticlinal  arch  the  sandstone  is  in  places 
broken  and  polished  with  slickensides  accomjDanying  slight  displacement 


42      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  the  rock.  A  well-marked  bench  occurs  along  the  top  of  the  steep  slope 
or  escarpment,  its  surface  in  places  sloping  with  the  dip  of  the  strata.  It  is 
most  pronounced  when  above  the  harder  beds,  especially  where  these  are 
overlain  by  the  more  friable  sandstone  and  soft  shales  of  the  Juratrias 
formations. 

The  bench  is  well  developed  on  both  sides  of  the  drainage  channel 
running  west  from  Fawn  Pass.  Upon  entering  the  terrane  of  the  Juratrias 
formations,  which  are  mainly  fissile  limestones  and  shales,  passing  down- 
ward into  the  sandstones  of  possible  Triassic  age,  and  passing  upward  into 
the  friable  sandstones  underlying  the  Dakota  conglomerate,'  we  again 
encounter  intruded  sheets  of  igneous  rock.  These  intrusive  sheets  are 
nearly  conformable  with  the  sedimentary  strata,  following  the  shale  belts 
for  long  distances,  and  only  occasionally  breaking  up  across  the  strata 
to  follow  higher  horizons.  The  first  of  these  intrusive  sheets  met  with 
above  the  Carboniferous  limestones  occurs  in  the  base  of  the  Juratrias 
shales  below  the  Ellis  shale  beds,  and  forms  a  cliff  rising  above  the  bench 
west  of  Fawn  Pass.  The  sheet  of  aiidesite-porphyry  is  possibly  200  feet 
thick  at  this  place.  It  can  be  traced  west  and  east  from  this  exposure,  con- 
tinuing at  nearly  the  same  horizon.  The  shale  in  contact  with  the  poi'phyry 
is  more  or  less  baked,  and,  like  the  igneous  rock,  resists  erosion  better 
than  the  altered  shales,  thus  leading  to  the  formation  of  blutfs  or  ledges. 

Above  this  porphyry  cliff  the  country  slopes  gradually  and  stretches 
eastward  to  Fawn  Pass,  rising  abruptly  to  the  triangular  peak  1^  miles 
southwest  of  Gray  Peak.  This  comj^aratively  level  country  occupies  the 
axis  of  a  flat  synclinal  arch  that  dips  to  the  northwest.  The  strata  bend 
around  from  the  gentle  northeast  dip  through  a  northwesterly  one  to  a 
southwest  dip  of  15°  to  20°,  in  which  position  they  form  the  triangular 
peak  just  mentioned.  It  is  evident,  from  a  study  of  the  region,  that  this 
southwesterly  dip  is  due  to  the  intrusion  of  a  large  body  of  igneous  rock 
connected  with  the  bysmalith  of  Gray  Peak.  The  highest  sedimentary 
rock  in  the  triangular  peak  is  Dakota  conglomerate.  It  occurs  again  high 
up  on  the  west  spur  of  Gray  Peak,  where  it  dips  toward  the  northeast. 
The  ridge  between  these  points  traverses  an  anticlinal  arch  of  Jurassic  beds 
that  bend  over  the  igneous  mass  already  mentioned.  The  shales  include  at 
least  two  thin  sheets  of  igneous  rock,  each  from  40  to  100  feet  thick.  One 
of  these,  in  the  mass  of  the  triangular  peak,  thins  out  perceptibly  toward  the 


REGION  NORTH  OF  GALLATIN  RIVER,  43 

southwest.  The  coiTesponding  intrusive  sheets  beneath  the  Dakota  con- 
glomerate in  the  southern  slope  of  Gray  Peak  thin  out  towai-d  the  east,  and 
near  the  end  of  the  spur  one  of  them  breaks  upward  as  a  dike-like  body 
across  the  Dakota  conglomerate. 

The  porphyry  forming  the  axis  of  this  small  arch  extends  south, 
constitutmg  the  ridge  of  Fawn  Pass.  It  extends  east  down  the  valley  of 
Fawn  Creek  as  an  intrusive  sheet  near  the  base  of  the  Juratrias  shales,  and 
extends  south  of  Fawn  Pass  as  an  intrusive  sheet  at  the  same  horizon,  and 
has  been  traced  as  a  ledge  along  the  ridge  south  and  westward  to  the  cliff 
first  described  north  of  Gallatin  River.  It  becomes  thinner  as  it  is  followed 
farther  from  the  bysmalith,  and  it  is  e\'ident  that  the  intrusive  sheets  in 
this  vicinity  proceeded  from  the  Gray  Peak  intrusive  mass. 

The  sedimentary  beds  forming  the  mountain  side  south  of  Gray  Peak 
dip  into  the  mountain  toward  the  north  and  northeast  at  a  low  angle  and 
encounter  the  igneous  rock  of  the  bysmalith  which  forms  the  highest 
portion  of  the  mountain  mass  from  Gray  Peak  to  Joseph  Peak,  and  extends 
down  the  east  slope  to  a  level  of  9,000  feet  and  down  the  west  side  to  below 
this  altitude.  The  igneous  rock  extends  along  tlie  north  face  of  the  ridge 
west  of  Gray  Peak.  From  it  also  proceed  sheets  of  porphyry  intruded 
between  the  Juratrias  strata  which  are  exposed  along  the  south  face  of 
Little  Quadi-ant  Mountain  and  may  be  traced  around  the  northern  slopes. 

On  the  northern  side  of  the  mass  the  sedimentary  beds  dip- toward  the 
southeast,  into  the  igneous  core  Again,  as  at  the  southern  side  of  this 
body,  the  highest  horizon  is  that  of  the  Dakota  conglomerate  which  is 
found  at  the  summit  of  Joseph  Peak  in  contact  with  the  intruded  mass. 
As  may  be  seen  from  the  map  and  cross  sections  (Pis.  IX  and  X),  there  is 
a  quaquaversal  arching  of  the  strata,  the  center  of  which  is  located  in  the 
head  of  Fan  Creek,  northwest  of  Joseph  Peak.  From  this  point  the  beds 
dip  south,  southeast,  east,  northeast,  north,  and  northwest.  In  the  three 
valleys  heading  against  the  ridge  surrounding  this  arch  the  beds  dip  to 
the  east,  northeast,  and  north  at  angles  not  far  from  10° — in  some  cases 
reaching  25°. 

At  the  west  end  of  the  ridge  north  of  this  part  of  Fan  Creek,  the  beds 
arch  over  to  the  west  and  southwest  with  a  dip  of  20°,  and  pitch  against 
the  same  fault  plane  noted  north  of  Gallatin  River  which  let  down  the 
volcanic    breccia.     Between   the    sedimentarv    strata,  sheets    of    andesite- 


44      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

poi-phyry  have  been  intruded  exactly  as  on  the  southern  and  eastern  sides  of 
the  bysmahth.  The  lowest  one  exposed,  however,  is  beneath  the  Juratrias 
beds,  immediately  above  the  Carboniferous  limestone.  It  appears  around 
the  head  of  Fan  Creek,  thinning-  out  northward.  Within  the  Ellis  shales, 
beneath  the  Dakota  conglomerate,  there  are  five  thin  sheets  of  intrusive 
rock  on  the  northern  slope  of  Joseph  Peak.  Three  of  these  have  been 
recognized  north  of  the  saddle  between  Fan  Creek  and  Gardiner  River. 
They  grow  thinner  and  less  noticeable  to  the  northwest,  and  may  be  traced 
down  the  east  slope  of  Joseph  Peak,  where,  on  account  of  the  position  of 
the  beds,  they  form  isolated  patches.  These  sheets  vary  in  thickness  from 
16  or  20  to  100  feet. 

Above  the  Dakota  conglomerate  and  sandstone,  the  shales  and  sand- 
stones that  alternate  with  one  another  through  a  thickness  of  nearly  3,000 
feet,  constituting  the  Colorado  and  Montana  formations,  take  part  in  the 
quaquaversal  arching  already  described — that  is,  on  the  northern  side.  On 
the  south  they  have  been  removed  by  erosion.  In  the  ridge  noi'th  of  Fan 
Creek  they  dip  to  the  northwest  and  north,  curving  over  to  a  northeasterly 
dip  in  the  ridge  connecting  this  with  Electric  Peak,  throughout  which 
latter  ridge  they  maintain  a  generally  uniform  dip  to  the  northeast,  con- 
tinuing the  same  attitude  beyond  the  boundary  of  the  Yellowstone  Park  to 
the  synclinal  trough  at  Horr.  In  the  ridge  between  the  head  branches  of 
Gaidiner  Kiver,  these  beds  curve  from  an  easterly  dip  near  its  west  end 
to  a  northeasterly  one  farther  down  the  ridge,  and  in  Little  Quadrant 
Mountain  they  also  maintain  a  general  northeasterly  dip,  as  already  noted. 

The  alternation  of  shales  and  sandstone  layers  seems  to  have  been 
particularly  favorable  to  the  intrusion  of  sheets  of  igneous  magmas.  The 
fissile  shale  offered  numerous  planes  of  weakness  and  parting,  while  the 
sandstone  layers  tended  to  stifi"en  the  strata  and  cause  the  splitting  to  follow 
more  nearly  constant  horizons,  for  though  there  is  some  cross  fracturing  of 
the  sedimentary  beds,  where  the  igneous  rock  may  be  seen  crossing  the 
strata  to  higher  horizons,  yet  the  persistency  of  the  intrasive  sheets  is  one 
of  their  marked  features.  This  is  observed  both  upon  actual  exjjosures 
over  long  distances  and  upon  the  comparison  of  geological  sections  made 
across  the  strata  by  several  observers  in  numerous  localities. 

In  the  ridge  north  of  Fan  Creek  the  Colorado  shales  form  the  northern 
slope  and  steep  spurs  and  a  small  portion  of  the  western  end.     Directly 


THE  FAN.  45 

above  the  Dakota  oong-lonierate  tlie  shales  are  spht  by  two  thin  sheets  of 
aiidesite-porphvry,  and  also  by  a  massive  layer  that  appears  as  a  small  lac- 
colith constituting-  the  northwestern  end  of  the  ridge.  The  petrographical 
character  of  the  sheets  is  not  the  same  in  all  cases,  but  the  distinctions  are 
slig-ht  and  will  be  discussed  in  Chapter  II.  In  the  high  ridge  between  the 
head  branches  of  Gardiner  Kiver,  at  least  five  different  sheets  of  andesite- 
porphyry  were  observed,  having  the  general  dip  of  the  shales  and  sandstones, 
with  occasional  ruptures  across  the  beds.  They  were  also  found  crossing 
the  valley  to  the  north  and  forming  part  of  the  ridge  leading  to  Electric 
Peak,  as  represented  on  the  map.  Their  thicknesses  are  not  constant,  as  may 
be  seen  in  their  exposui'es,  but  the  actual  variation  is  greatly  exaggerated 
in  appearance  by  the  positions  of  the  exposures,  whether  directly  across  the 
thickness  or  more  or  less  parallel  to  the  sheet.  This  impression  is  still 
further  increased  by  the  appearance  produced  by  the  more  persistent  talus 
slopes  of  the  harder  porphyry,  which  often  obsciire  more  easily  removable 
areas  of  the  softer  shale.  The  same  sheets  occur  in  the  shales  in  the  upper 
part  of  Little  Quadrant  Mountain. 

THE  FAN. 

Fan  Creek  drains  the  mountainous  area  whose  various  spurs  converge 
to  the  west  at  the  ribs  of  the  Fan,  from  which  resemblance  the  region 
derives  its  name.  The  encircling  ridge  which  forms  the  divide  between 
the  waters  of  Fan  Creek  and  those  of  the  Gallatin  and  Gardiner  drainages 
culminates  in  two  prominent  peaks,  one  of  which.  Gray  Peak,  has  already 
been  described.  The  other,  lying  to  the  north,  is  named  Joseph  Peak,  and 
occupies  a  commanding  position  just  west  of  Little  Quadrant  Mountain. 
The  southei'n  fork  of  Fan  Creek  is  named  Stellaria  Creek.  At  the  head  of 
this  stream  the  high  ridge  which  is  the  southwestern  extension  of  Gray 
Peak  is  formed  of  Mesozoic  beds,  having  a  strike  of  N.  20°  E.  and  a  dip  of 
10°  W.  The  peak  is  formed  of  Dakota  sandstone  resting  upon  the  Jura- 
trias  beds,  and  is  cixt  by  intrusive  sheets  of  andesite-porphyry  from  the 
Gray  Peak  bysmalith,  as  already  described  on  page  42. 


46  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  TARK. 

The  following  section  represents  the  beds  exposed  on  the  northern  slopes 
of  this  ridge  at  a  point  just  west  of  the  9,900-foot  peak: 

Section  at  ridge  southwest  of  Gray  Peak. 

Num- 
ber. Feet. 

3    Dakota  conglomerate  and  sandstone;  pebbly  in  layers,  but  much  of  it  a  fine-grained  sand- 
stone, buff  with  red  and  white  blotches,  and  cross  bedded 60 

2    Shaly  beds,  very  arenaceous  and  light  brown  at  top;  softer  and  more  argillaceous  below, 
where  the  layers  are  generally  a  blue-black  and  contain  some  splintery  limestone.     The 

typical  rock  is  a  soft  argillaceous  sandstone,  light  gray,  weathering  brown 50 

Andesite-porphyry,  dark  gray,  compact;  rock  occurring  irregularly  columnar  in  ledges, 
with  two  or  three  layers  of  brown  altered  porphyry  with  fine  concentric  weathering 35 

1    Limestone,  gray  with  rusty  speckling,  saccharoidal  texture.     The  upper  8  feet  soft  and 

purple  shale,  weathering  brown 18 

Strike,  N.  20'^  E. ;  dip,  8^-10^^  W. 

On  the  west  side  of  this  peak,  100  feet  below  the  summit,  the  black 
shales  are  well  exposed  and  form  the  crest  of  the  ridge  down  to  the  saddle. 
West  of  the  saddle  they  give  place  to  the  Dakota  sandstone,  which  extends 
westward  to  the  cliffs  indicated  upon  the  map.  Farther  west  the  ridge 
shows  a  succession  of  light-gi-ay  limestones  overlying  the  red  Teton  sand- 
stones. The  latter  beds  form  red  slopes  that  extend  westward  to  the 
andesite-porjihyry  hill  shown  upon  the  map. 

The  central  ridge  of  the  Fan,  lying  north  of  Stellaria  Creek  and  west 
of  Joseph  Peak,  is  a  long  flat-topped  mass  with  grassy  meadows  and  dense 
forests  of  pine.  On  the  western  end  of  this  ridge  exposures  are  scarce  and 
must  be  sought  for  in  the  stream  channel.  A  short  distance  above  the  forks 
of  Fan  Creek,  Stellaria  Creek  has  cut  a  gorge  through  the  intrusive  sheet 
of  andesite-porphyry.  This  rock  is  also  exposed  on  the  south  slopes  of  the 
ridge  to  the  north  for  a  distance  of  2^  miles  above  the  mouth  of  Stellaria 
Creek.  The  rock  is  generally  much  decomposed,  of  a  light-buff  color, 
with  numerous  decomposed  acicular  hornblende  and  white  plagioclase 
phenocrysts.  The  porphyrj^  forms  great  heaps  of  tabular  dc^bris,  often 
arranged  in  ridges  running  apj^roximately  east  and  west  and  separated  from 
the  solid  rock  by  the  hollows  between  the  cliffs  and  these  morainal  ridges. 
These  hollows  are  often  without  outlet,  and  sometimes  hold  small  ponds. 
From  the  junction  of  the  stream  eastward  the  summit  of  the  ridge  shows 
no  outcrops  of  sedimentary  rocks,  the  covering  of  the  porphyry  sheet  just 
noticed  having  been  removed  by  erosion  and  the  summit  being  now  hea\aly 
mantled  with  glacial  drift,  which  seems  to  be  at  least  100  feet  thick  in  the 


JOSEPH  PEAK.  47 

transverse  drainage  channel.  This  transverse  drainage  channel,  which  runs 
northward  to  join  Fan  Creek,  forms  the  natural  boundary  line  between 
the  sedinientaries  on  the  east  and  the  andesite-porphyry  on  the  west.  The 
sedimentary  rocks  are  light-gray  limestones,  having  a  strike  of  S.  20°  W., 
and  a  dip  of  10°  W.,  which  would  carry  the  beds  under  the  drift  forming 
the  summit  of  the  ridge  to  the  west.  The  higher  slopes  to  the  east  show 
good  exposm-es  of  the  sedimentary  rocks.  A  western  spur  of  Joseph  Peak 
shows  the  following  section  of  sedimentary  rocks,  the  lowest  bed  exposed 
being  part  of  tlie  Quadrant  quartzites. 


Joseph  Peak  section. 


Num- 
ber. 


Feet. 


{5  Ked  bed.s,  calcareous  sandstones,  etc. 

4  Sandstone  and  limestones,  fissile,  gray,  weathering  brown-gray 25 

3  Limestone,  gray,  compact 10 

Teton      > 

limestones  \^  Cherty  sandstones  and  limestones 100 

Quadrant 

niiart?itps   '  ^  Sandstones,  quartzites,  and  interbedded  gray  limestones 300 


>  1     Sandstones,  quartzites,  and  interbedded  gray  limestones  . 


At  the  base  of  this  spur  the  summit  of  the  ridge  is  nearly  flat  and  is 
largely  strewn  with  chert  weathered  out  of  the  Teton  limestones.  The 
beds  here  apparently  dip  SE.  10°,  Avhich  takes  them  underneath  Joseph 
Peak.  The  cherty  beds  of  the  Teton  series  are  here  quite  well  exposed. 
The  chert  occurs  in  both  banded  and  nodular  forms,  and  is  so  abundant 
that  the  remaining  material,  which  is  generally  sandstone,  forms  but  a 
minor  feature.  In  seams  and  patches,  however,  the  rock  is  free  from  chert, 
and  is  then  much  more  calcareous  and  contains  fragments  of  fossils.  North 
of  the  spur  from  Joseph  Peak  the  Teton  limestone  beds  dip  W.  8°,  and 
strike  S.  8°  E.  Farther  north  the  flat  summit  of  the  ridge  is  formed  of  a 
fine-grained  andesite-porphyry,  whose  rust-colored  exposures  much  resem- 
ble those  of  the  sedimentary  rocks.  This  rock  forms  the  summit  of  a  bold 
cliff  to  the  north.  This  cliff",  which  is  about  500  feet  high,  shows  excellent 
exposures  of  the  Quadrant  quartzites  resting  upon  Madison  limestones, 
forming  the  channel  of  Fan  Creek,  and  capped  just  beneath  the  andesite- 
porphyry  by  the  cherty  beds  of  the  Teton  series.  This  exposure  shows  a 
total  thickness  of  350  feet  of  Quadrant  quartzite  and  125  feet  of  the  Teton 
limestone.  The  character  of  the  cherty  limestones  varies  from  a  dove- 
colored,  nearly  pure  limestone  to  a  granular  brown  sandstone  which  is  not 


48      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

calcareous.  The  talus  at  the  base  of  the  cliffs,  like  that  of  the  andesitic 
intrusive  of  Stellaria  Creek,  is  arranged  in  morainal  ridges,  with  a  depres- 
sion between  these  heapings  and  the  base  of  the  cliff.  The  valley  of 
Fan  Creek  has  been  cut  in  the  low  anticline,  exposing  the  Madison  lime- 
stones overlain  by  the  Quadrant  quartzites,  with  the  softer  Mesozoic  rocks 
forming  higher  slopes  to  the  north.  In  the  small  drainage  cutting  the 
slopes  north  of  the  creek  the  following  section  was  measured: 

Fan  Greeh  section. 

Num-  Feet, 

ber. 

(  15    Dakota  conglomerate  and  sandstone,  the  latter  gray,  with  white  spots, 

*  °'"  (14    Sandstone,  rusty  yellow,  blotched  with  piuk,  slightly  calcareous 125 

(•13    Limestone,  dark  gray,  crystalline 5 

12    Limestone,  fissile  and  shaly,  gray 15 

lie  Arenaceous  limestone,  gray,  crumbly,  rusty 1 

EDig         116  Sh.iles  and  crumbly  limestones 2 

sandatoue.  1  Ha  Limestone,  crysfcilline,  gray,  dense,  splintery,  argillaceous 1 

10    Arenaceous  limestone,  or  calcareous  sandstone,  light  brown-gray 15 

9    Limestone,  grading   at  top  into  No.  10.     The  limestone  is  pure  and  full  of 

fossils 15 

8    Limestone,  argillaceous,  soft,  crumbly 10 

7    Argillaceous  limestones,  crumbly,  containing  fossils,  and  with  interbedded 

layers  of  harder  crystalline  limestone 140 

6    Red  shales 20 

5    Green  and  blue  shales 30 

4     Interval (?) 

3    Cherty  beds 125 

2    AVhite  sandstones,  etc 300 

1     Limestone,  crystalline,  creamy,  with  patches  of  red  magnesian  limestone 30 


Ellis      J 
limestone.  | 

Teton       I 
shales.      | 

Teton  ) 
limestone.  \ 
Quadrant  ( 
quartzite.  ^ 
Madison 
limestone 


The  summit  of  the  ridge  north  of  Fan  Creek,  already  mentioned  on 
page  43,  forms  what  might  be  termed  the  northern  rib  of  the  Fan  and 
is  capped  by  Dakota  beds,  whose  persistent  nature,  combined  with  that 
of  the  intrusive  sheets  of  andesite-porphyry,  has  left  the  ridge  sharply 
defined.  The  Dakota  conglomerate  is  but  20  feet  thick  and  is  overlain  by 
buff-colored  and  pink  sandstones  similar  to  those  mentioned  in  the  section 
just  given.  At  the  head  of  Fan  Creek  a  depression  in  the  mountain  ridge 
forms  a  pass  to  the  headwaters  of  Gardiner  River.  The  western  slopes  of 
this  pass  are  thickly  covered  with  soil  and  vegetation,  and  no  exposures 
are  seen,  but  to  the  east  the  beds  are  well  exposed  where  the  streams  from 
the  snow  banks  of  the  ridge  have  washed  the  surface  of  the  rocks  bare  of 


Ellis 
limestone 


FAN.PASS.  49 

soil.  The  saddle  itself  is  toniu'd  of  liiuestoues  broken  throiiii-h  hv  juidesite- 
porphyr\-.  The  folhtwiug-  section  shows  the  series  of  beds  exposed  from  the 
pass  to  the  snnnnit  of  the  peak  to  the  north: 

Fan  I'ass  section. 

Num- 
l"r.  Feet. 

Dakota.         S       Dakota  coiiu'lomerate  and  saudstono;  creamy,  pink,   broken   tlirongli   by  an- 

de.'iite  porphyry ^0 

(  11)     I>iniestone,  bard,  gray,  crystalliuo,  weathering  brown 10 

7«     Limestone,  granular,  arenaceous,  light  drab 15 

Ellis       J  (!      Limestone,   more  or  less   arenaceous  in  certain  bauds,  fossililerons.      Strike, 

sandstone.  1             N.45-'  W.;  dip,  2.")-  N 75 

I  oft     Limestone,  soft  and  sandy ; 1q 

\  5a     ]>imestone,  arenaceous,  gray-brown 5 

I  ib     Ked  shale,  crumbly  and  soft g 

in     Sliite ;  metamorphosed  by  audesite-porphyry 2 

.Vndesite-jiorphyry- 

3      Limestones,  soft,  crumbly,  very  argillaceous,  with  harder  crystalline  layers; 

very  fossil iferons 5g 

2      Limestone,  finely  crystalline,  weathers  brown,  somewhat  slialy 5 

1      Limestone,  shaly,  broken  through  by  andesite-porphyry 45 

To  the  east  of  Fan  Pass  an  extension  of  the  anticlinal  uplift  noted 
to  the  west  brings  up  the  red  shales  and  sandstones  from  the  upper  portion 
of  the  Teton  formation.     From  the  summit  of  the  mountain  peak  north  of 
Fan  Pass  the  ledge  extends  in  a  northwest  direction  until  it  meets  the  long 
southwestern  spur  of  Electric  Peak.     The  Dakota  conglomerate  forms  the 
crest  of  the  ridge  as  far  as  the  second  peak  north  of  Fan  Pass,  and,  as 
already  noted,  the  same  rock  extends  westward,  forming  the  crest  of  the 
encircling  ridge      The  summit  of  the  second  peak  north  of  Fan  Pass  is 
formed  of  andesite-porphyry.     This  rests  upon  Dakota  conglomerate  and 
is  overlain  by  cherty  limestone,  which  is  apparently  part  of  the  Dakota 
limestones,  but  is  of  different  habit  and  carries  light  greenish-yellow  chert. 
Between  this  point  and  the  10,100-foot  peak  to  the  northeast  a  succession 
of  beds  is  exposed  in  which  the  shales  are  cut  by  intrusive   sheets  of 
andesite-porphyry.     The  Dakota  limestone,  somewhat  metamorphosed,  but 
•showing  the  crystalline  marks  and  the  little  gasteropod  shells  so  character- 
istic of  this  horizon,  is  overlain  by  very  splintery  greenish-yellow  shale, 
weathering  brown.     This  in  turn  is  capped  by  a  baked  sandstone  about  20 
feet  thick,  which  is  overlain  by  the  upper  quartzite  belt  of  the  Dakota 
series,  the  bed  being  here  30  feet  thick.     The  carbonaceous  shales  of  the 
Benton  formation  form  the  ridge  from  this  point  eastward  to  the  slopes  of 

MON  XXXII,  PT  II 4 


50  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Electric  Peak.  The  shales  are  cut  by  numerous  intrusive  sheets  of 
andesite-porplivry  and  b}'  a  few  dikes,  one  of  which  cuts  the  10,100- 
foot  peak  already  noted.  In  the  sandstone  bed  intercalated  in  the  lower 
part  of  the  Benton  shales  the  little  oyster,  Ontrea  anomioides,  occurs 
abundantly.  The  beds  here  have  a  dip  of  10°  N.,  the  strike  being  N. 
75°  E.  The  andesitic  sheets  noted  on  this  ridge  ai-e  continuous  for  long 
distances,  their  ledges  being  traceable  along  the  slopes  ou  either  side  of 
the  ridge.  In  general,  the  andesitic  sheets,  being  less  easily  eroded  than 
the  soft  black  shales,  form  the  high  points  and  mountainous  summits  of  the 
ridge,  while  the  saddles  are  cut  in  the  softer  rocks. 

ELECTRIC  PEAK. 

Electric  Peak  is  the  highest  and  most  imposing  summit  of  the  Gallatin 
Range.  Its  apex  rises  boldly  above  the  adjacent  mountains,  and  the  long 
ridges  which  form  its  foundations  dominate  the  country  for  many  miles. 
The  mountain  is  composed  of  sedimentary  rocks  of  Cretaceous  age,  broken 
through  and  in  part  largel}'  altered  by  igneovis  rocks.  The  sedimentary 
rocks  only  will  be  treated  here,  as  these  igneous  rocks  and  their  occurrence 
are  of  such  interest  that  a  special  chapter  is  devoted  to  them. 

The  sedimentary  rocks  composing  the  mountain  embrace  the  most 
recent  strata  of  the  sedimentary  series  to  be  found  in  the  Gallatin  Range, 
including  a  thickness  of  4,300  feet  of  Cretaceous  beds,  whose  uppermost 
portion  is  coal-bearing  and  belongs  to  the  Laramie.  Complete  sections 
may  be  studied  at  two  localities.  One  is  the  southeastern  spur  of  the  peak, 
where  the  beds  are  sharply  upturned  against  the  Gallatin  fault;  the  other 
is  the  long  northern  ridge  of  the  peak  which  terminates  in  that  mass  of 
upturned  and  exposed  strata  known  as  Cinnabar  Mountain.  Although  the 
latter  locality  lies  just  outside  the  limits  of  the  Park,  the  section  there 
exposed  is  typical  for  the  region,  and,  combined  with  the  sections  already 
given  of  the  Teton,  Ellis,  and  Dakota  formations,  it  forms  a  complete  sec- 
tion of  the  Mesozoic  strata  of  the  range. 


Section  of  beds  exposed  on  southeast  sjmr  of  Electric  Peak. 

Nam- 
ber. 

f  22    Carbonaceous  sliale '40 

Anilesite-porphy ry ■10 


Feet. 


s 

g  '  5  '  Carbonaceoiis  shale 100 


« 


o  Andesite-porpby  ry ^0 

I  Carbouaceous  shale 300 

.500 


9 


U  S  GEOLOGICAL  SURVEY 


MOHooFAPH XXXII, fart:;  ?L  ll< 


CROWFOOT  RIDGE 


OUNT  HOLMES 


EMIGRANT  PEAK 


THE  CRAGS 


«gn 


SEPULCHRE   MOUNTAIN 


ELECTRIC  PEtt- 


GRAY  PEAK  JOSEPH  PEAK 


ELECTRIC  PEAK 


EMIGRANT  PEAK 


SEPULCHRE  MT- 


GEOLOOICAL  SKCTIONS  ACHOSS  CALLATLX  HANOK 

I.KIVKNL) 

CRETACEOUS  JURATRIAS  CARBONIFEROUS  CAMBRIAN 

ik/h    i^'    h    B    H    Hi'    'CK 

Scale  oF  Miles 


r^y^ 


ELECTRIC  PEAK  SECTION. 


51 


Scctimi  of  beds  c.qjoscd  on  southeast  spur  of  Electric  I'eal- — Continued. 

Niini- 
bor. 

21     Cnlcareous  saiidstonos,  chan;;ing  to  pure  Siindstoues  at  the  bottom 

20     S;iii(lsti)iio,  mottled  and  carbonaPrDiis 

ly     Sandstone,  indurated  and  argiUaeeous 

,  18    Sandstones,  speckled 

Andesite-porpliyry,  much  decomposed 

17    Calcareous  sandstone 

16    Sandstone,  indurated,  argillaceous 

Andesite-porphy  ry 

Interval,  no  exposure 

15    Limestone,  very  impure,  argillaceous  and  arenaceous 

Interval,  no  exposure 

14     Indurated  sandstone 

13     Shales,  very  dark  slate-colored,  argillaceous  rocks  which  are  poorly  exposed 

12    Sandstone,  indurated  to  granular  quartz ite 5 

Interval,  no  exposure 75 

Indurated  sandstone 10 


11 


Lio 

f   9 


r  6 

I    5 


W  I 


i:  J 


^    V 


Sandstones  and  arenaceous  limestones,  -with  two  intruded  sheets  of  andesite-por- 
phyry  aggregating  15  feet  in  thickness 

Interval,  no  exposure,  hut  showing  debris  of  dark-colored  carbonaceous  shales 
belonging  to  bed  helow 

Andesite-porphyry,  much  decomposed 

Carbonaceous,  argillaceous  shale 

Sandstone 

Interval,  no  exposure 

Limestone 

Interval,  no  exposure 

Conglomerate  and  sandstone,  broken  through  l)y  andesite-porphyry 

Arenaceous  limestone 

Arenaceous  limestones,  passing  downward  into  sandstones,  cross  bedded,  and  chang- 
ing to  limestones  near  base 

Interval,  no  exposure 

4  Sandstone,  dark  gray,  mottled  with  carbonaceous  matter,  fine  grained  and  not  indu- 
rated  

Interval,  no  exposure 

3     Limestone 

Interval,  no  exposure 

2    Quartzite  and  highly  indurated  calcareous  sandstones 


^) 


IS  L 


Limestone,  light  cream  colored;  bands  of  red  limestone  exposed  along  north  bank 

of  Gardiner  River,  200  feet  below  top 

Limestone,  brownish  gray,  dense 


Ft-et. 

175 
1)1) 
20 
10 
15 
30 
50 
30 

10.) 
10 

100 
10 

300 


(10 
160 

300 

15 

100 

20 

50 

5 

50 

5 


45 

50 

5 

100 

100 

15 

200 


250 

50 


Total  thicliness  of  section. 
Thickness  of  intrusive  sheets 


3,47« 
148 


Total  thickness  of  sedimentary  rocks •. 3,  330 


52  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  audesite-porphyvies  of  this  section  occur  as  sheets  intruded  along 
the  planes  of  bedding-  of  the  sedimentary  rocks.  With  one  exception 
intrusion  is  regular  and  does  not  break  across  the  bedding  planes  of  the 
shale.  The  dip  and  strike  of  the  beds  vary  in  passing  upward  from  Gardi- 
ner River  to  the  summit  of  the  peak.  In  many  cases  this  change  of  dip 
is  apparent  in  the  exposure,  but  in  most  cases  the  outcrop  is  not  suffi- 
ciently extensive  to  make  the  flexure  apparent. 

The  long  southwestern  spur  of  Electric  Peak,  which  has  already  been 
noted,  shows  sheet  after  sheet  of  andesite-porphyry  cutting  across  the  crest 
of  the  ridge  and  intruded  in  the  dark  shales  of  the  Colorado  formation, 
the  beds   dipping    NE.  about  10°.      Three   different  bodies  of  andesite- 
porphyry  have  broken  through  one  another  in  the  high  point  southwest  of 
the  peak.     One  of  these  intrusions  may  be  traced  eastward  along  the 
southern  slope  of  the  mountain  for  some  distance.     The  western  slope  of 
the  mountain  shows  the  sedimentary  and  igneous  layers  in  strong  relief, 
and  they  may  be  distinguished  at  a  distance.     The  inclination  of  these 
ledges  is  about  10°  N.,  corresponding  to  the  greater  dip,  which  is  to  the 
northeast.    The  sheets  of  igneous  rock  are  seen  to  follow  the  bedding  planes 
of  the  strata  for  considerable  distance.     Only  one  sheet  was  seen  break- 
ing up  across  the  strata  and  proceeding  along  the  higher  horizon.     The 
direction  of  this  uprising  is  from  sovith  toward  the  north,  and  this  occur- 
rence, together  with  observations  made  on  the  eastern  side  of  the  moun- 
tain, showing  a  similar  rise  from  the  west  to  the  east  and  a  thinning  out 
of  the  sheets  in  the  same  direction,  indicates  that  these  intrusive  masses 
were  injected  from  the  southwest— that  is,  probably  from  the  center  occu- 
pied by  the  Gray  Peak  bysmalith.     The  intrusive  sheets  vary  from  a  few 
feet  to  a  hundred  or  more  feet  in  thickness.     The  rocks  differ  slightly  in 
petrographical  character  and  will  be  described  more  fully  in  Chapter  II. 
The  peak  itself  is  formed  of  the  soft  shales  and  thinly  bedded  sandstones 
belonging  to   the    Colorado    and    Montana   formations.     These  rocks  are 
penetrated  by  a  number  of  intrusive  dikes  of  andesite-porphyry,  and  the 
sedimentary  series  is  much  altered  by  the  great  intrusion  of  igneous  rock 
forming  the  volcanic  core  east  of  the  peak.     On  the  summit  of  the  peak  the 
normal  sandstones  and  shales  are  altered  to  slates  and  quartzites,  the  rocks 
being  much  shattered  by  joints  and  breaking  readily  into  short,  angular 
ddbris.     The  beds  dip  N.  10°  to  20°. 


ELKCTUIC  PEAK, 


53 


The  intrusive  sheets  extend,  in  Jiininishin<>'  numbers,  northward  in  tlie 
north  ridge  of  Ek'ctrii'  Peak.  The}'  i-esenibk^  the  sheets  intrude<l  in  tlu^ 
Jurassic  shales  of  Cinnabar  Mountain,  thoug-h  it  is  ])ossible  that  tlie  latter 
intrusive  rocks  were  derived  from  other  sources  more  directly  connected 
with  the  synclinal  folding  and  faulting  of  Cinnabar  Mountain. 

Tlie  north  ridge  of  Electric  Peak  terminates  in  the  low  knob  called 
Cinnabar  jMountain.  This  elevation  is  formed  of  upturned  sedimentary 
beds,  presenting  a  most  excellent  and  complete  section  of  the  stratigraphic 
series  from  the  Paleozoic  to  the  summit  of  the  Laramie,  a  section  which  is 
here  given,  as  it  is  typical  for  the  Gallatin  region.' 

Section  of  the  Mesozoic  sedimentary  rocks  exposed  in  Cinnabar  Mountain  and 

Electric  Peal: 


i\ 


Sandstones  alternating  with  shales  and  carrying   coal    .seams,    many   of  ivhieb   are 
workable 


|-  White,  massive,  and  cross-bedded  sandstone,  easily  disintegrated  and  crumbling  readily 
I      under  pressure 

Impure  sandstone,  gray  in  color,  carrying  argillaceous  material  and  often  calcareous. 
The  outcrops  frequently  weather  into  flagstones  a  few  inches  thick,  forming  broken 
reefs  that  project  above  the  smoother  slopes 

Alternating  fissile  sandstones  and  impure  argillaceous  shales  which  frequently  carry 
lenses  of  purer  sandstone,  and  near  the  base  contain  much  bituminous  shale,  which  is 
soft  and  crumbly  upon  weathering 

Arenaceous  shales  and  shaly  sandstones,  generally  greenish  gray  in  color,  and  weathering 

into  line  brown  df^bris 

'  Sandstones,  generally  forming  ledges  projecting  above  the  slopes  of  shale 

Gray  shales  and  shaly  sandstones 

Soft,  bituminous,  black  shale,  weathering  readily  and  forming  a  smooth  slope  covered 
with  the  fine  fragments  of  the  leafy  shale 

Calcareous  beds,  varying  from  impure  arenaceous  limestones  to  calcareous  shale 

Black  shales,  alternating  with  thin  arenaceous  beds,  and  containing  strata  of  blue 
splintery  limestones  which  are  argillaceous,  dense  in  structure,  and  do  not  form  per- 
sistent horizons 

Quartzite,  forming  a  reef  that  projects  as  a  wall  above  the  slopes  of  shale 

Black  and  dark-blue  shales,  varying  from  arenaceous,  light-gray,  impure  sandstones  to 
black,  laminated,  bituminous  shales,  and  carrying  the  same  impure  dark-blue  lime- 
stones found  above 

Sandstone,  generally  massive,  gray  in  color,  weathering  with  a  rusty  surface;  fissile, 
granular  in  texture,  and  forming  a  wall  projecting  above  the  slope 

Sandstone,  very  fissile,  and  grading  into  an  arenaceous  shale 

Impure  limestone,  passing  into  argillaceous  black  shales  and  arenaceous  shales 

Dark-colored,  bUiish-black,  finely  laminated  shales  with  occasional  interbedded  Saud- 
is    stones 


Feet. 
800 

125 
240 

450 

226 

38 

164 

500 
40 

400 
5 

350 


15 
50 

265 


'  See  Cinnabar  and  Bozemau  coal  fields,  by  W.  H.  Weed:  Bull.  Geol.  Soc.  Am.,  Vol.  II,  1891,  p.  3.52. 


■ 

C3 

O 

s 

C3 

e 

Q 

o 

- 

54      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Section  of  the  Mesozoic  sedimentary  rocks  exposed  in  Cinnabar  Mountain,  etc. — Cont'd. 

Feet. 

Quartzite  rhangiug  to  sandstone,  light  gray,  dense  in  texture,  and  forming  a  prominent 
wall  15  to  20  feet  wide 5q 

Limestones,  blue-gray  in  color  but  weathering  to  a  creamy  buff  tint  on  the  surface.  The 
rock  is  dense  in  texture  and  shows  the  remains  of  the  same  gasteropods  found  in  the 
beds  of  Little  Quadrant  Mountain.  In  the  Cinnabar  section  this  intermediate  horizon 
includes  a  portion  of  the  thickness  given  to  the  Dakota  conglomerate,  but  it  is  char- 
acterized by  red  maguesian  limestoues  which  possess  many  characters  similar  to  those 
of  the  volcanic  ash  beds  found  farther  north  above  the  Dakota  conglomerate,  and 
passing  into  sandy  shales  which  are  capped  by  10  feet  of  quite  pure  limestone 75 

Dakota  conglomerate  and  sandstone 175 

f  Reddish  shales  and  impure  limestones 85 

Limestoues  and  calcareous  sandstones,  occasionally  a  conglomerate;  carries  an  abun- 
dance of  fossil  remains,  which  are  generally  fragmentary  near  the  bas<i 75 

Red  argillaceous  shale $ 

Gray  calcareous  shales  and  impure  limestones,  characterized  by  an  abundance  of  fossil 
remains,  particularly  iu  the  upper  strata.  The  beds  are  separated  near  the  center  by 
oolitic  limestoues 132 

Green  and  red  shales 50 

Sandstone,  saccharoidal  in  texture,  generally  light  gray  or  bufi'  in  color,  but  red  or  browu 
on  weathered  surface 50 

Red  beds,  consisting  of  very  fissile  sandstones  and  impure  arenaceous  clays 75 

Limestone,  compact  in  texture,  gray  iu  color,  and  carrying  remains  of  liugulas 20 

■§  *  Limestones,  dark  gray  in  color,  generally  fetid,  often  arenaceous,  and  frecjuently  char- 
acterized by  rod-like  masses  of  chert,  which  are  seen  to  consist  of  grains  of  sand 

embedded  in  the  siliceous  matrix,  the  concretions  having  a  white  chalky  surface 125 

[  Quadrant  iiuartzites. 

The  western  face  of  Electric  Peak  shows  a  number  of  sheets  of  iffiieous 
rock,  varying  from  5  to  50  feet  in  thickness;  but  no  dikes,  either  vertical 
or  incHned,  were  observed  on  this  side  of  the  mountain.  The  western 
summit  consists  of  a  sheet  of  andesite-porphyry  several  hundred  feet  thick. 
In  the  eastern  spurs  of  the  mountain  numerous  vertical  and  inclined  dikes 
cut  the  ujjturned  beds.  Those  on  the  southeastern  spur  trend  to  the  south- 
west and  northeast.  They  also  traverse  the  eastern  summit  of  Electric 
Peak.  The  southeastern  spur  of  the  mountain  shows  steej^ly  upturned 
sedimentary  l)eds,  which  at  the  base  are  overthrown  and  reversed.  This 
spur  probably  consists  of  a  synclinal  fold  which  was  accompanied  by 
faulting,  the  eastern  limb,  forming  the  lower  portion  of  the  spur,  having 
a  nearly  vertical  position.  The  axis  of  the  syucline  has  a  trend  to  the 
southwest  and  northeast.  The  overthrown  beds  at  the  southern  extrem- 
ity of  this  spur  show  Madison  limestones.  Quadrant  quartzites,  and  the 
regular  sequence  of  overlying  Mesozoic  strata.  The  beds  strike  north, 
and  they  dip  from  50°  to  70°  E.      The  Gardiner  River  cuts  across  the 


ELKGTHIO  PEAK.  55 

t'lul  of"  this  spur,  tlic  rocks  being  exposed  in  a  small  hill  on  the  south- 
western side  of"  the  stream,  the  channel  having  j)robably  been  deflected  at 
this  place  by  the  accumidatiou  of  glacial  drift  filling  the  old  valley 
between  Sepulchre  Mountain  and  Little  Quadrant.  A  detailed  section 
of  the  beds  ex})osed  on  the  crest  oi  this  ridge  has  been  given.  The 
strike  of  the  beds  varies  somewhat  in  ascending  the  s})ur,  and  the  dip 
also  changes.  The  Dakota  ledge,  which  crosses  the  ridge  about  500  feet 
above  the  river,  has  a  strike  of  N.  32°  E.,  showing  a  considerable  change 
in  direction  between  the  ex[)osures  here  and  those  in  the  river  bed.  The 
axis  of  this  synclinal  fold  and  the  fault  plane  are  found  high  up  on  this 
southeastern  spur,  where  the  Colorado  shales  have  a  vertical  dip.  The 
exact  position  of  the  fault  plane  can  not  be  determined,  and  the  extent  of 
displacement  is  not  known.  That  the  intrusive  sheets  of  igneous  rock 
antedated  the  folding  is  clearly  shown  in  the  crushing  and  slight  dynamic 
metamorjjhism  observed  here.  Slickensides  are  found  within  the  porphyry, 
and  dragging  planes  are  observable  between  the  hard  eruptive  rock  and 
the  soft  shales.  A  coue-in-cone  structure  of  the  latter  rocks  is  also 
observed.  On  the  other  hand,  the  dikes  of  igneous  rock  which  cut  this 
spur  of  the  mountain  show  no  sign  of  disturbance  attributable  to  the 
synclinal  folding.  They  intersect  sedimentary  beds,  and  also  the  inter- 
calated sheets  of  porphyry,  at  various  angles.  Where  the  shales  and 
intrusive  sheets  are  on  edge,  the  dikes  are  often  parallel  to  them  and  are 
easily  confused  with  the  intrusive  sheets,  which  they  closely  resemble  in 
petrographical  character.  These  dikes  are  connected  with  a  large  body 
of  igneous  rock,  mostly  a  diorite,  which  occupies  a  position  on  the  line  of 
faulting  and  is  situated  in  the  deep  gulch  cut  in  the  eastern  summit  of 
Electric  Peak.  The  sedimentary  beds  in  the  neighborhood  of  this  mass 
of  igneous  rock  are  extensively  metamorphosed. 

At  the  eastern  base  of  Electric  Peak  a  profound  fault  separates  the 
mountain  mass  from  the  complex  body  of  volcanic  tuff-breccias  and  massive 
igneous  rocks  to  the  east.  This  fault  is  the  northern  continuation  of  the 
Gallatin  fault,  which  has  given  rise  to  the  abrupt  escarpment  faces  on  the 
east  side  of  the  Gallatin  Range. 

On  account  of  the  special  importance  of  the  relations  existing  between 
the  igneous  rocks  of  Electric  Peak  and  those  forming  Sepulchre  Mountain 
to  the  east  of  the  fault,  a  detailed  description  of  the  geology  of  this  locality 
is  given  in  Chapter  III,  in  which  the  petrology  also  will  be  fully  discussed. 


56      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 
WESTERSr  FLANKS  OF  THE  GALLATIN  RAKGE. 

In  the  northwestern  portion  of  the  Gallatin  Range,  within  the  Yellow- 
stone Park,  the  western  slopes  of  the  mountains  are  abruptly  terminated 
by  a  fault,  bringing-  up  the  sedimentary  beds  against  subaerial  volcanic 
breccias  that  probably  represent  a  remnant  of  the  old  Electric  Peak  and 
Sepulchre  Mountain  volcanic  cone.  The  fault,  where  it  crosses  Fan  Creek 
and  along  its  course  down  Cinnabar  Creek,  shows  a  profound  displacement. 
Its  southern  continuation  has  already  been  noted  west  of  Gray  Peak,  but 
it  becomes  of  slight  importance  in  the  vicinity  of  Grayling  Creek,  west  of 
the  end  of  Crowfoot  Ridge.  The  andesitic  breccias  which  form  the  high 
mountain  ridges  west  of  this  fault  are  continuous  with  the  high  range  of 
the  Gallatin  which  stretches  northward  along  the  western  side  of  the 
Yellowstone  River  to  the  vicinity  of  Bozeman.  Within  the  park  region 
the  underlying  upturned  and  irregularly  eroded  sedimentary  beds  are  not 
exposed.  The  position  and  dip  of  the  strata  forming  the  high  ridge  on  the 
eastern  side  of  the  Gallatin  River,  just  within  the  northwestern  corner  of 
the  park,  show  a  monoclinal  structure  which  would  bring  the  Montana 
shales  and  sandstones  beneath  the  andesite  breccias  and  against  the  Fan 
Creek  fault.  It  is  clear  that  the  horizon  west  of  the  fault  was  consid- 
erably higher  than  that  to  the  east,  for  the  latter  is  near  the  base  of  the 
Colorado  shales  and  contains  laccolithic  sheets,  which  must  have  been 
intruded  at  considerable  depths  beneath  the  surface  of  the  country,  and 
were  contemporaneous  with  those  intruded  in  the  upper  part  of  the  Colo- 
rado formation  of  Electric  Peak,  which  is  but  3  miles  distant.  Another 
fact  that  is  apparent  is  that  the  sedimentary  strata  were  upturned  and 
eroded  down  to  the  Carboniferous  sandstone,  7  miles  to  the  west,  before 
the  volcanic  breccias  were  thrown  out  over  the  country. 

The  only  other  andesitic  tuff-breccia  in  this  vicinity  occurs  in  isolated 
patches  resting  directly  upon  crystalline  schists  in  the  neighborhood  of 
The  Crags,  5  and  10  miles  south  of  the  breccia  west  of  Gray  Peak,  and 
from  13  to  17  miles  distant  from  the  Electric  Peak  center  of  the  eruption. 
From  these  facts  it  would  appear  that  the  surface  of  the  country  at 
the  time  when  the  andesitic  tuff-breccias  were  deposited  consisted  of 
crystalline  schists  in  the  south,  of  Carboniferous  strata  in  the  west,  and 
of  Cretaceous  strata  in  the  northeast.     This  indicates  the  uplifting  of  the 


U  S  GEOLOGICAL  SURVEY. 


MONOGRAPH  XXXII.PART  II, PL  X. 


MONTANA 
"WYOM/Nd"  "k 

/        anp 


"0  50'        BOUNDARY 


-.  ■;  5 


GEOLOGICAL  MAP 

OF 

GALLATIN  RAN^GE , YELLOWSTONE  NATIONAL  PARK. 


A.Hoen&Co.Litb.Ballir>i 


PLEISTOCENE 


CRETACEOUS 


LEGEND 

JURATRIAS 


CARBONIFEROUS  DEVONIAN      SILURIAN 


Phs 

Pal 

Pgd 

Km 

Kc 

M 

'  Je  " 

Jt 

'  Cq  'i 

Cm 

tfr: 


Sj 


Hot  Springs    AUnviran.        Glacial        Montana       Coloraflo        Dakota  Ellis  Totoii         Quadrant       Madison 

formation  drift.         formatioii-.    formatioii.     fomiatioiL    formation,     formation,    formation,    limestone. 


CAMBRIAN 


NEOCENE 


EOCENE 


Thi"eot()rt(s 
limestone. 


ARCHEAN 


JetfersoH 
limestone. 


H 


Nbst 


Nrh 


Nel 


Nebb 

Eeab 

dp 

anp 

-fl^n 

— 

Gallatin        PJathead 
limestone,     formation- 


Basalt. 


Rliyolite.        Khmiiir       Kersanlite.    Earlv basic    f^ailv  acid        UaciUi-         Andtisite- 
intrusives.  breccici.         breccia.      porphyry,      porphyi'y. 


Graiiilo  and 
s^nciss. 


Yaoilts. 


^-^-^£-^-S- 


Scale    12SOOO 

■  f  f  ? 


CONTOUR  INTERVAL  lOO  FEET. 


MADISUN  liANGE.  57 

sedimentary    strata    and    their    tilting'   iKirthward,    followed    by    extensive 
erosion  at  the  south  prior  to  the  extravasation  of  tlie  andesitic  breccia. 

We  have  already  jjointed  out  the  connection  between  the  hitrusion  of 
the  Holmes  bysmalith  and  the  fault  traversing  the  eastern  end  of  Crow- 
foot Rido-e,  noting  their  probable  contemporaneity.  The  intrusion  of  the 
Holmes  mass  nuxst  have  been  followed  by  extensive  erosion  before  the 
cr'S'stalline  schists  were  exposed  at  the  level  they  now  occupy  relative  to 
the  Holmes  mass,  after  which  erosion  the  andesitic  breccias  were  thrown 
ujjon  them.  This  separates  the  eruption  of  the  Holmes  bysmalith  and  that 
of  the  andesitic  breccias  by  a  very  considerable  length  of  time.  No  definite 
time  relation  has  been  made  out,  however,  between  the  two  great  intrusive 
bodies  at  the  southern  end  of  the  Gallatin  Range — Indian  Creek  laccolith 
and  Holmes  bysmalith — and  the  more  complex  intrusion  of  Gray  Peak 
and  the  associated  sheets  of  andesite-porphyry  in  the  northern  part  of  the 
range.  Though  separated  by  only  a  small  distance,  there  is  no  structural 
feature  which  connects  their  intrusions  in  point  of  time,  except  the  general 
fact  that  the}^  are  all  much  older  than  the  eruptions  that  centered  at  Electric 
Peak. 

EASTERN  FliANK  OF  THE  MADISON^   RANGE. 

In  the  extreme  northwestern  corner  of  the  Yellowstone  Park  there  is  a 
small  area  of  mountainous  country  that  is  part  of  the  eastern  flank  of  the 
Madison  Range.  This  area  lies  wholly  within  the  Montana  portion  of  the 
reservation.  The  Gallatin  River  has  cut  a  narrow  valley  across  this  tract, 
exposing  folded  strata,  in  which  the  same  sedimentary  series  seen  in  the 
Gallatin  Range  is  developed,  the  lowest  rocks  belonging  to  the  Cambrian 
and  the  highest  being  of  Colorado  Cretaceous  age.  These  strata  are  flexed 
about  a  laccolith  of  andesite-porphyry. 

This  mountain  area  is  terminated  on  the  south  by  the  northern  end  of 
the  rhyolite  plateau,  whose  lavas  cover  the  southeastern  flanks  of  the  high 
mountain  east  of  the  Gallatin  River  and  also  occur  in  small  isolated  patches 
upon  the  mountain  slopes  to  the  north  and  west. 

Topographically  this  little  tract  consists  of  parts  of  four  distinct  moun- 
tain masses.  The  largest  lies  east  of  the  Gallatin  and  is  embraced  between 
that  river  and  Fan  Creek.  This  block  and  that  north  of  it,  and  the  flat- 
topped  mountain  west  of  the  Gallatin  River,  are  all  parts  of  the  lacco- 
lithic  uplift,  which  has  been  cut  through  by  the  river.     The  east  bank 


Three  Forks 
and 

Jefferson. 


58      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  the  Gallatin  shows  an  excellent  exposure  of  the  contact  between  the 
andesite-porphyiy  and  the  Cambrian  shales,  the  latter  being  altered  by 
contact  metaniorphism  for  a  few  feet  from  the  andesite-porphyry.  The 
Cambrian  shales  are  overlain  l^y  limestones  in  which  there  are  intruded 
several  sheets  of  andesite-porphyry,  and  are  capped  by  cliffs  of  a  heavily 
bedded  white  limestone  of  the  Madison  formation,  with  basic  intrusions, 
near  tlie  summit  of  the  mountain.  The  following  partial  section  shows  the 
series  found  immediately  above  the  laccolith : 

Section  east  of  Gallatin  River,  below  Fan  Creel: 

Feet. 
Madison.  Limestones  carrying  cdrals,  thickly  bediled,  of  a  dense  texture,  drab  or  dark-gray 

colored,  and  holding  black  chert. 
Limestone  shale  of  pink,  red,  buff,  and  pnrplish  colors,  carrying  a  few  fossils  and 

underlain  by  dark-blue  (almost  black)  limestone 200 

Andesite-porphyry,  poorly  exposed 25 

Granular,  dark-brown  and   black  limestone,  sometimes  banded,  and  of  Silurian 

aspect 15 

Thinly  bedded  and  fissile  light-gray  limestone,  dense  and  not  crystalline,  impure 

and  carrying  argillaceous  matter 5 

Uark-colored  granular  limestone,  carrying  Obolella 12 

Limestone,  thinly  bedded  and  with  a  knotty  texture,  dark  blue  in  color,  of  typical 

Cambrian  aspect,  and  evidently  of  shallow-water  origin 30 

Limestone  shale,  blue  and  olive  gray  in  color 5 

Limestone,  dense  in  texture  and  dove  colored 5 

Limestone,  becoming  shale ;  dip  mO"^  to  the  east 5 

Shales,  green  or  olive  colored,  seldom  exposed 15 

Limestone,  mottled,  of  typical  Cambrian  aspect 15 

Shale 5 

Andesite-porphyry  laccolith. 

West  of  the  Gallatin  River  the  mountain  slopes  show  andesite-porphyry 
extendino-  up  nearly  to  the  summit  of  the  flat-topped  mountain,  but  the 
stratified  rocks  are  seen  both  to  the  north  and  to  the  south,  forming  great 
cm-ved  plates,  with  dip  away  from  the  intrusion  in  every  direction.  A 
stream  from  the  west  has  cut  its  valley  in  the  dome,  exposing  the  sedi- 
mentary rocks  on  the  valley  walls. 

The  mountain  opposite  the  mouth  of  Fan  Creek  is  composed  entirely 
of  Paleozoic  strata,  which  are  not  affected  by  the  laccolithic  uplift,  but  dip 
to  the  east  and  northeast,  away  from  the  axis  of  the  Madison  Range.  The 
lower  slopes  show  Cambrian  beds,  which  are  overlain  by  the  Silurian 
rocks,  of  which  the  most  prominent  strata  are  quartzitic  in  nature  and  form 
heavy,  massive  beds  that  cap  the  summit  of  the  mountain  and  extend  east- 


Gallatin. 


MADISON  RANGE.  59 

ward  down  to  tlie  valley  of  the  Gallatin  Kiver,  the  dip  being  about  20°. 
The  summit  of  the  mountain  is  flat,  and  shows  Carboniferous  limestones 
dijiping  northeast  at  gentle  angles.  This  mountain  and  the  one  north  of 
it  both  show  the  characteristic  flat-to2')ped  topography  noticed  in  the  lesser 
marginal  peaks  of  the  Madison  Range. 

The  andesite-porphyry  of  the  laccolith  is  (p^ite  like  those  rocks  in  the 
Gallatin  already  described,  and  its  petrographic  description  is  given  in 
another  chapter.  A  chai'acteristic  feature  of  the  exposures  seen  of  this  rock 
is  the  occurrence  of  numerous  included  fragments  of  gneiss,  schist,  and 
hornblende-porphyry.  The  two  patches  of  rhyolite  which  occur  upon  the 
slopes  rest  directly  upon  this  andesite-porphyry,  showing  a  thorough  dis- 
section of  the  laccolithic  fold  before  the  outpouring  of  the  rhyolite  flows. 


CHAPTER    11. 

THE    INTRUSIVE    ROCKS   OF    THE   GALLATIN    MOUNTAINS, 
BUNSEN  PEAK,  AND  MOUNT  EVERTS. 


By  Joseph  Paxson  Iddings. 


Having  described  the  occurrence  of  the  igneous  rocks  that  have  been 
intruded  within  the  sedimentary  beds  of  the  Gallatin  Mountains,  or  have 
been  thrown  over  their  surface,  so  far  as  their  occurrence  is  related  to  the 
history  of  the  dynamic  events  that  brought  about  the  present  structure 
and  topography  of  the  range,  we  may  now  describe  their  petrographical 
characters  in  relation  to  the  mode  of  their  occurrence,  ^vith  special  reference 
to  the  size  of  the  various  bodies  of  rock  and  then*  geological  position. 

From  what  has  already  been  shown  as  to  the  relative  age  of  the 
different  intrusions,  it  will  be  proper  to  consider  them  in  the  following 
order:  Indian  Ci'eek  laccolith;  Holmes  bysmalith  and  connected  outliers; 
Bighorn  Pass  sheet;  Gray  Mountain  intrusive  and  connected  sheets; 
Electric  Peak  stock  and  dikes,  together  with  the  extrusive  breccias  and 
intrusive  dikes  of  Sepulchre  Mountain;  and  the  breccias  west  and  south  of 
the  Gallatin  Range.  In  this  connection  may  also  be  described  the  Buusen 
Peak  intrusive  and  the  intrusive  sheets  in  Mount  Everts. 

INDIAIi^  CREEK  LACCOLITH. 

HORNBLENDE-MICA-ANDESITE-PORPHYRY. 

The  rock  constituting  this  laccolith  and  its  two  sheet-like  apophyses  to 
the  south  is  an  intrusive  mass,  quite  uniform  in  mineral  composition 
throughout  its  whole  extent.  It  exhibits  a  limited  variability  in  texture 
and  habit,  ranging  from  those  of  a  compact  aphanitic  or  lithoidal  lava  to 
those  of  a  minutely  crystalline  porphyry-like  rock.  Its  predominant  min- 
eral constituents  are  lime-soda  feldspar,  hornblende,  and  biotite,  with  a 
small  amount  of  magnetite  and,  in  the  coarser-gi-ained  forms,  quartz.  For 
this  reason  it  may  be  called  an  andesite-porphyry  with  andesite  facies.     Its 

60 


INDIAN  CKEEK  LACCOLITH. 


61 


chemical  coin]iositinn  is  rr'wen  below.  The  portion  of  tlie  rock  analyzed 
was  the  unalt(;reil  coarser-g-rained  form  (55)'  occurring  in  the  middle  of 
the  laccolith  on  the  north  side  of  Indian  Creek. 

,1  iKilysis  of  hornhlende-micaandesite  porphyry. 

[Analyst,  J.  E.  Wliitfleld.  1 


Coustitueut. 


sio, 

TiOj 

AI2O3 

FecO:, 

FeO 

MnO 

MgO 

CaO  

Li;0 

NajO 

K.O 

P2OB 

SO-, 

H;0 

Total 


Per  cent. 


61.  50 

None. 

17.42 

4.66 

1.09 

Trace. 

1.26 

5.  33 

.03 

3.99 

1.29 

.60 

.35 

2.44 


99.96 


The  main  body  of  the  laccolith,  where  it  is  about  1,000  feet  thick,  is 
a  light-gray  rock  crowded  with  small  crystals  of  feldspar,  mica,  and  horn- 
blende, with  a  subordinate  amount  of  groundmass,  whose  component  grains 
are  not  discernible  with  the  naked  eye.  The  phenocrysts  are  1  or  2  mm.  in 
diameter  and  smaller;  occasional  ones  reach  3  mm.  The  rock  is  distinctly 
massive,  cracking  with  irregular  joints  into  angular  or  somewhat  tabular 
fragments,  and  exhibiting  columnar  jointing  hi  only  one  locality,  on  the 
southeast  slope  of  The  Dome.  Under  the  microscope  the  most  crystalline 
portion  of  the  laccolith  (57),  which  proved  to  be  the  eastern- central  part  of 
the  mass  on  the  south  side  of  Indian  Creek,  is  seen  to  consist  of  the  pheno- 
crysts already  named,  cemented  together  by  a  holocrystalline  aggregation 
of  quartz  and  feldspar  with  scattered  grains  of  biotite,  hornblende,  and 
magnetite  (PI.  XI,  lig.  1).  The  areas  of  quartz  inclose  minute  idiomorphic 
feldspar,  in  part,  if  not  wholly,  lime-soda  feldspars,  probably  oligoclase. 
The  quartz  is  allotriomorphic  and  has  a  micropoikilitic  structure,  the  grains 


'  Numerals  in  brackets  used  in  connection  with  the  petrography  in  this  monograph  refer  to  the 
specimen  numbers  in  the  Yellowstone  Park  collection. 


(32  GEOLOGY  OF  THE  YELLOWSTONE  XATIO^STAL  PARK. 

ranging  from  0.08  to  0.2  mm.  in  diameter,  the  inclosed  feldspars  being  about 
0.04  mm.  long  and  0.008  mm.  wide,  and  upward.  Somewhat  finer-grained 
forms  were  found  in  the  central  portions  of  the  mass  north  of  Indian  Creek. 
In  these  there  is  a  more  marked  difference  between  the  groundmass  and 
phenocrysts.  When  seen  under  the  microscope,  the  microstructure  of  the 
groundmass  is  more  evenly  granular,  the  grains  averaging  about  0.04  mm. 
in  diameter  in  one  case  (56),  and  about  0.024  mm.  in  another  (55).  This 
degree  of  crystallization  corresponds  to  grade  20  of  the  table  for  the  rocks 
of  Electric  Peak  (Table  XVII),  for  the  first  case,  and  to  grades  11  and 
9  of  the  same  table  for  the  last  two  respectively.  The  last  is  shown  in 
PI.  XI,  fig.  2. 

The  phenocrysts  are  not  sharply  outlined,  and  have  numerous  inclu- 
sions of  irregular  grains  or  streaks  of  quartz  and  feldspar.  The  feldspar 
phenocrysts  are  all  lime-soda  feldspar,  in  part  labradorite,  in  part  andesine. 
They  are  frequently  shattered,  with  irregular  cracks,  and  are  penetrated 
by  irregular  streaks  of  quartz  and  feldspar,  whicli  are  sometimes  granular. 
In  places  it  looks  as  though  the  groundmass  of  the  rock  had  penetrated 
cracks  in  the  feldspars  before  it  solidified.  The  feldspar  individuals  in  one 
rock  section  are  not  all  equally  fissured,  and  not  always  in  the  same  direc- 
tion, so  that  the  cracking  appears  to  antedate  the  solidification  of  the  rock. 
The  biotites  exhibit  very  slight  dislocation  or  bending  in  some  cases,  which 
may  be  referred  to  the  same  i:)eriod.  The  biotite  is  dark  brown,  with  mod- 
erate absorption  and  occasional  twinning.  The  outlines,  often  idiomorphic, 
are  sometimes  very  irregular,  there  being  marginal  inclosures  of  quartz  and 
feldspar,  and  sometimes  of  magnetite,  but  not  often.  The  hornblende  is 
green,  with  moderate  pleochroism  from  strong  green  to  light  bi'own.  The 
outlines  are  quite  irregular,  and  inclusions  of  the  other  minerals  are  fre- 
quent. There  is  sometimes  a  chloritic  mineral  present  in  small  pseudo- 
morphs,  which  may  possibly  l)e  altered  pj^roxene.  In  some  instances  it  is 
decomposed  hornblende.  Magnetite  is  present  in  microscopic  crystals, 
often  idiomorphic;  and  apatite  forms  colorless  microscopic  crystals.  Both 
hornblende  and  biotite  take  part  in  the  composition  of  the  groundmass  in 
the  more  crystalline  varieties. 

Somewhat  finer-grained  microcrystalline  structures  are  found  in  the 
rock,  where  it  forms  the  thinner  sheets,  100  to  150  feet  thick,  beneath  Trilo- 
bite  Point  (72,  73).  Here  the  structure  is  confused,  being  partly  micro- 
poildhtic,  partly  nncrogranular.     In  the  still  finer-grained  modifications  the 


U.  S.  QEOLOaiCAL    SURVEY 


MONOGRAPH    XXXII     PART   II     PL.   XI 


rA)  %   29 


rsj  X  3 1 


<C)  X  28 


(D)  X  45 


PHOTOMICROGRAPHS    OF  ANDESITE-PORPHYRY    AND    DACITE-PORPHYRY 


THE  HELIOTYPE  PRrNTINO  CO..  BOSTON 


INDIAN  CKEEK  LACCOLITH.  63 

inicropoikilitic  (nuirtz  patches  fjTow  less  and  less  noticeable,  and  tlic  feldspar 
inicrolites  become  more  [)ronounced,  the  microstructm-e  beiny  moi'e  like 
the  characteristic  t'elt-like  or  pilotaxitic  structure  of  andesites.  This  transi- 
tion occurs  as  the  rock  approaches  the  contact  with  inclosing  rocks,  and 
where  the  body  thins  out.  It  accompanies  a  darkening  of  the  rock  and  an 
iucreasino-ly  andesitic  habit.  The  rock  20  feet  from  the  bottom  contact 
near  the  east  edge  of  the  laccolith  north  of  Indian  Creek  is  bluish  gray, 
with  prominent  feldspars  that  are  decomposed  (OO).  The  hornblendes  are 
altered  to  chlorite  and  calcite.  Biotite  is  still  fresh.  The  s'roundmass  is 
holocrystalline  and  •  pilotaxitic.  Near  the  Ijottom  contact  of  the  middle 
poi'tion  of  the  main  laccolith  body  the  rock  grows  darker  and  denser.  At  6 
feet  from  the  contact  it  is  darker  gray  than  the  main  mass.  The  micro- 
structure  of  the  groundmass  is  micropoikilitic,  with  the  minute  feldspars 
maintaining  a  fluidal  arraugen^ent  (61).  The  rock  1  foot  from  contact  is 
darker  colored;  its  structure  is  still  micropoikilitic,  with  more  minute  feld- 
spars (62),  while  the  rock  directly  in  contact  with  the  limestone  is  still 
darker  and  the  microstructure  still  finer  grained  and  micropoikilitic  (63). 
There  is  considerable  calcite  scattered  in  irregular  microscopic  aggregates 
through  the  groundmass.  The  hornblendes  are  decomposed,  and  there  is 
some  secondary  quartz.  The  micropoikilitic  structure,  however,  is  not 
secondary,  as  seems  to  be  the  case  in  some  porphyries,^  since  it  varies  in 
size  of  grain  according  to  the  distance  from  the  contact  plane,  and  is  quite 
the  same  as  that  observed  in  perfectly  fresh  andesite-porphyries  in  other 
places.  Similar  modifications  occur  near  the  contact  of  the  andesite-porphyry 
with  the  inclosed  belt  of  limestone  in  the  central  part  of  the  laccolith  north 
of  Indian  Creek  (66).  The  feldspar  and  biotite  phenocrysts  are  fresh, 
while  the  hornblende  is  entirely  decomposed. 

"Where  the  andesite-porphyry  is  exposed  in  contact  with  the  overlying 
limestone  at  the  northwest  base  of  Three  River  Peak,  the  same  transition 
from  coarser-grained  to  finer-grained  groundmass  is  observed  (68,  69,  70, 
71).  The  rock  nearest  the  contact  is  very  dark  colored,  dense,  and  dis- 
tinctl)'  porphyritic,  and  under  the  microscope  is  found  to  have  the  micro- 
structure  of  a  holocrystalline  andesite — that  is,  the  groundmass  consists  of 
microlites  of  feldspar  and  pyroxene,  with  scattered  grains  of  magnetite,  and 


'Williams,  G.  H.,  on  the  use  of  the  terms  poikilitic  and  micropoikilitic  in  petrography:  .Jour. 
Geol.,  Vol.  I,  No.  2,  1893.  p.  179.  Baseoiu,  F.,  The  stnutiires,  origin,  aud  nomenclature  of  the  acid 
volcanic  rocks  of  South  Mountain  :  Jour.  Geol.,  Vol.  I,  No.  8,  1893,  p.  814. 


64      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

has  au  ill-defined  micropoikilitic  structure.  Among  the  phenocrysts  are  a 
few  irregular  individuals  of  quartz. 

The  closest  approach  to  typical  andesitic  microstructure  occurs  in  the 
dike  cutting  shales  in  the  ridge  south  of  Winter  Creek,  already  described 
(p.  10).  The  transition  from  a  groundmass  of  brown  microcryptocrystalline 
matrix  with  distinct  lath-shaped  feldspar  microlites  and  magnetite  grains  to 
one  that  is  gray  in  thin  section  with  larger  feldspar  laths  and  a  slightly 
micropoikihtic  structure  can  be  observed  in  one  rock  section  IJ  inches 
long  (76).  The  finest-grain  is  at  the  contact  with  the  inclosing  rock.  The 
dike  is  3  feet  wide  and  the  central  portion  is  slightly  more  crystalline. 
There  is  a  pronounced  fluidal  arrangement  of  the  feldspar  microlites,  more 
or  less  parallel  to  the  sides  of  the  dike.  The  hornblende  and  biotite  are  both 
altered  to  chlorite,  which  also  fills  the  centers  of  the  feldspar  phenocrysts, 
leaving  a  clear  marginal  zone.  Magnetite  occurs  in  phenocrysts  and  in 
minute  crystals  in  the  groundmass.  Whatever  ferromaghesian  minerals 
may  have  been  constituents  in  the  groundmass  have  been  chloritized,  and 
there  is  no  evidence  that  they  were  present  in  any  considerable  amount. 
In  the  rock  from  the  horizontal  sheet  in  this  ridge  of  limestone  the  ground- 
mass,  which  is  coarser  grained,  contains  abundant  microlites  of  mica  and 
altered  hornblendes,  with  minute  magnetites.  These  minerals  are  also 
abundant  as  phenocrysts.  Apatites  and  long,  thin,  doubly  terminated 
crystals  of  zircon  occur.  Except  for  this  slightly  more  ferroraagnesian 
modification  of  the  rock  (74),  the  mineralogical  composition  of  the  laccolith 
is  very  uniform  throughout  the  whole  of  its  exposure,  which  covers  a  dis- 
tance of  7  miles. 

Segregations  occur  in  places.  Tliey  consist  of  comparatively  coarse- 
o-rained  crystallizations  of  green  hornblende,  with  brownish  tones,  marked 
pleochroism,  and  orthopinacoidal  twinning,  besides  lime-soda  feldspar,  in 
part  labradorite,  with  magnetite,  some  biotite,  and  a  little  quartz  and  grains 
of  calcite;  the  whole  having  a  hypidiomorphic  granular  structure. 

MOUNT  HOLMES  BXS3IALITH. 

DACITE-PORPHYRY. 

The  rock  constituting  this  great  body,  which  embraces  the  mass  of  five 
mountain  peaks,  and  is  3  miles  long  and  2  miles  wide,  is  very  uniform  in 
general  appearance  through  the  whole  extent  of  the  body.  It  is  grayish 
white,  with  few  small  phenocrysts  of  feldspar   and  biotite,  and  has  a  fine- 


MOUNT  HOLMES  BYSMALITH. 


65 


grained  to  aphanitic  texture.  It  is  not  markedly  porphyritic.  The  variations 
in  texture  occur  near  the  margin  of  the  body,  where  they  bear  a  definite 
relation  to  the  contact  plane.  They  are  accompanied  by  a  slight  change  in 
the  chemical  composition.  The  uniformity  in  the  character  of  the  mass 
indicates  that  the  whole  body  was  one  magma,  erupted  at  one  time.  Its 
mineral  composition  is  seen  with  the  microscope  to  be  quartz  and  alkali 
feldspar  with  biotite,  corresponding  to  that  of  biotite-granite.  Its  chemical 
composition  is  shown  by  the  following  analyses,  one  of  which  represents 
the  main  mass  of  the  rock;  the  other,  which  is  more  siliceous,  is  of  rock 
from  near  the  margin  of  the  bysmalith,  at  Echo  Peak. 

Analyses  of  dacite-porphyry  and  rliyolite-felsite. 

[Analyst,  J.  '&.  Wljitfield.] 


Constituent. 

(77) 
Mount 
Holmes. 

(87) 
Echo  Peak. 

SiOii 

69.54 

None. 

17.95 

2.50 

.22 

None. 

.50 

1.80 

Trace. 

4.30 

1.21 

None. 

.37 

1.96 

74.51 

None. 

14.83 

1.09 

Trace. 

Trace. 

.47 

.81 

.02 

4.38 

2.72 

Trace. 

.24 

.92 

TiOj 

AID, 

F.,03 

FeO 

MuO 

MgO 

CaO 

Li02 

NaO 

K2O 

P.O5 

SO3            

H,0 

Total 

100.  35 

99.99 

The  chemical  composition  corresponds  to  that  of  a  granite  high  in  soda. 
The  main  mass  has  a  chemical  composition  just  on  the  border  line  between 
soda-rhyolite  and  dacite,  while  the  marginal  portion  has  the  composition  of 
soda-rhyolite.  As  already  noted,  its  texture  is  not  markedly  porphyritic,  so 
that  it  stands  between  a  distinct  jDorphyry  and  a  felsite.  It  is,  consequently, 
difficult  to  give  it  a  name  that  will  not  be  open  to  criticism.  We  have  called 
the  main  mass  dacite-porphyry. 

In  thin  section  the  rock  appears  as  a  gray,  very  fine-grained  mass  with 
abundant  minute  specks  of  biotite.     Under  the  microscope  it  is  seen  that 

MON  XXXII,  PT  11 5 


66      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

the  microstructure  and  grain  of  the  rock  from  the  summit  and  south  slope 
of  Mount  Hohiies  (77,  78),  and  those  of  the  rock  from  the  White  Peaks  west 
of  the  head  of  Indian  Creek  (80,  81,  82),  ai-e  very  uniform,  and  represent  the 
coarsest-grained  forms  found.  The  highest  part  of  the  mass  as  it  now 
exists,  the  summit  of  Mount  Hohnes,  is  nearly  as  coarsely  crystallized  as 
any  part  of  the  body  examined. 

The  coarsest  varieties  consist  of  quartz  in  allotriomorphic  individuals, 
inclosing  nearly  idiomorphic  crystals  of  feldspar,  with  fewer  of  biotite  and 
magnetite.  The  structure  is  thus  micropoikilitic,  or  is  almost  exactly 
analogous  in  the  relative  proportions  and  sizes  of  the  crystals  to  microphitic 
structure  in  ophitic  basalt.  The  quartz  extinguishes  light  between  crossed 
nicols  throughout  small  areas,  in  which  are  scattered  more  or  less  rectangular 
and  lath-shaped  feldspars.  The  quartzes  are  colorless  and  have  few  inclo- 
sures  of  liquid  with  moving  bubbles  and  salt  cubes.  The  feldspars  are 
cloudy  and  partly  altered;  hence  the  minerals  are  easily  distinguished.  The 
structure  is  shown  in  PI.  XI,  fig.  3.  The  feldspars  are  partly  unstriated,  in 
Carlsbad  twins,  with  low  extinction  angles  and  low  double  refraction;  these 
are  probably  orthoclase;  others  are  partly  striated,  in  polysynthetic  twins, 
with  low  extinction  angles,  and  are  lime-soda  feldspars,  probably  oligoclase. 
It  appears  as  thougli  the  latter  predominated.  The  few  phenocrysts  are 
striated  lime-soda  feldspars.  Owing  to  the  low  percentage  of  calcium  oxide 
in  the  rock,  the  feldspars  must  correspond  to  plagioclase  rich  in  soda.  In 
one  instance  the  feldspar  contains  inclusions  of  what  appears  to  be  glass, 
but  its  exact  nature  is  doubtful.  Biotite  occiu-s  in  six-sided  plates  and  as 
irregular  individuals,  with  brown  color  and  strong  absorption.  They  often 
■contain  minute  magnetite  grains.  The  biotite  is  sometimes  in  small  aggre- 
gates with  magnetite,  which  also  occurs  in  scattered  crystals.  Apatite  is 
present  in  long  slender  prisms,  but  is  rare.  In  some  cases  it  exhibits  a 
distinct  blue  and  brownish-pui-ple  pleochroism.  Minute  zircon  prisms  are 
present. 

Among  the  secondary  minerals  is  a  little  muscovite  in  radiating  tufts. 
Chlorite,  resulting  from  the  alteration  of  biotite,  is  occasionally  noticed. 
The  decomposition  of  the  feldspar  produces  a  dust-like,  indeterminable 
mineral,  white  by  incident  light  and  yellowish  in  transmitted  light. 

In  the  dacite-porphyry  of  Echo  Peak  there  are  occasional  inclosures 
of  what  seems  to  be  coarse-grained  gneiss.  The  only  specimen  examined, 
however,   shows  a  coarse-grained  rock  with  somewhat  gneissic  structure, 


MOUNT  HOLMES  BYSMALITH.  67 

but  composed  of  the  same  minerals  as  the  dacite-ijorpliyry:  alkah  feldspar, 
quartz,  and  biotite,  with  magnetite  and  zircon.  The  niicroscopical  char- 
acters of  these  minerals  are  like  those  of  the  minerals  in  the  porphyry, 
and  it  is  possible  that  these  coarse-g-rained  inclosures  may  be  nothing  but 
coarsely  crystalline  portions  of  the  dacite  magma.  The  gneissic  structure 
may  be  the  result  of  irregular  differentiation,  as  in  the  case  of  the  banded 
g-abbro  of  Skye,'  described  by  Geikie  and  Teall. 

The  transition  from  the  more  coarsely  crystalline  central  ])ortion  to 
the  denser  and  tiner-grained  aphanitic  marginal  portion  is  shown  in  the 
changes  in  microstructure  in  specimens  (83,  84,  86,  87,  88)  collected  from 
Echo  Peak  and  in  the  contact  zone  in  the  gulch  between  this  and  Tlu-ee 
River  Peak. 

As  the  constituent  minerals  become  smaller  the  poikilitic  quartz  in  two 
cases  (84,  86)  assumes  more  of  an  idiomorphic  form,  interrupted  by  small 
feldspar  crystals  lying  at  various  angles.  The  quartz  sections  appear  in 
nearly  rhomljic  forms,  the  direction  of  extinction  being  diagonal  to  the 
rhombs.  The  crystals  are  more  or  less  perfect  hexagonal  bipyramids,  formed 
by  ±  R-  They  sometimes  lie  in  a  finer-grained  mixture  of  feldspar  and 
quartz,  which,  however,  does  not  amount  to  a  groundmass,  being  in  rela- 
tively small  quantity.  In  other  cases  the  finer-grained  modifications  of  the 
rock  are  still  micropoikilitic,  and  have  essentially  the  same  structure  as  the 
coarser  kinds.  It  would  seem  as  though  the  idiomorphism  of  the  quartzes 
occurred  in  cases  where  the  feldspar  was  a  little  more  abundant.  The  rock 
from  which  the  second  analysis  (87)  was  made  is  minutely  micropoikilitic. 
This  aphanitic  variety  is  niottled  with  small  dark  sjiots  that  prove  to  be 
chlorite,  containing  small  scales  and  j^lates  of  muscovite,  which  also  occui's 
scattered  through  the  rock  in  small  amount.  No  biotite  is  present.  Mag- 
netite occurs  in  small  crystals.  The  chlorite  and  muscovite  are  seen  in 
some  cases  to  be  alteration  products  of  biotite,  so  that  in  all  the  specimens 
examined  it  may  be  assumed  to  have  had  the  same  origin. 

This  more  lithoidal  or  aphanitic  form  of  the  rock  occurs  in  broad 
bands  parallel  to  the  plane  of  contact  around  the  margin  of  the  bysmalith. 
The  banding  is  recognizable  at  a  distance,  and  is  shown  in  the  photograph 
(PI.  XII)  of  the  north  side  of  Echo  Peak.  The  banding  stands  at  steejj 
angles,  which  are  more  nearly  vertical  in  lower  exposures,  suggesting  a 

'Geikie,  A..,  and  Teall,  J.  J.  H.,  On  the  banded  structure  of  some  Tertiary  gabbros  in  the  Isle  of 
Skye:  Quart.  Jour.  Gaol.  Soc,  Loudon,  Vol.  L,  No.  200,  1894,  pp.  645-660. 


68      GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PAEK. 

dome-like  shape  to  the  bysmalith.  The  rock  of  the  bands  is  massive,  the 
banding  being  due  to  dififerences  in  the  constituents  or  in  the  colors  and 
texture,  and  not  to  parallel  jointing.  In  the  vicinity  of  Echo  Peak,  on  its 
north  side,  the  banding  jjitches  downward  at  30°  to  35°,  passing  under  the 
tilted  limestone.  Very  close  to  the  contact  with  limestone  the  jjorphyry 
or  felsite  is  dense  and  slaty  (94),  being  split  into  thin  plates  parallel  to  the 
contact  plane.  These  are  traversed  by  numerous  irregular  joints,  which 
break  it  into  sherdy  pieces  at  right  angles  to  the  contact  plane.  In  places 
it  carries  quartz  phenocrysts,  and  has  the  appearance  of  a  quartz-porphyry. 

The  dense  aphanitic  variety  is  fine  grained  and  without  phenocrysts. 
It  is  holocrystalline,  with  the  small  quartzes  idiomorphic  and  the  feldspars 
less  so,  though  many  of  the  small  feldspars  are  idiomoi'phic,  and  the 
structure  approaches  panidiomorphic-granular.  The  average  size  of  the 
quartzes  is  about  0.03  mm. 

A  very  similar  modification  of  this  rock  forms  an  intrusive  sheet  or 
apophysis  from  the  bysmalith  in  the  limestone  and  shale  beneath  the 
Indian  Creek  laccolith  on  the  north  side  of  the  valley  of  Indian  Creek  (95). 
It  resembles  the  last-described  variety  in  megascopical  habit  and  platy 
parting  and  in  microstructui'e,  but  the  idiomorphism  of  the  quartz  is  less 
pronounced.     The  thickness  of  the  sheet  is  not  known. 

The  marginal  modification  of  the  bysmalith  is  well  shown  in  the 
mountain  ridge  west  of  The  Dome  and  north  of  Mount  Holmes.  The  same 
broad  banding  is  present,  the  position  of  the  bands  being  almost  vertical  in 
the  southern  exposure,  where  the  contact  is  visible  for  hundreds  of  feet. 
The  central,  more  crystalline  form  of  the  rock  passes  into  a  more  plainly 
porphyritic  zone,  and  this  into  an  aphanitic  zone,  Avhich  is  spotted  near  its 
contact  with  the  surrounding  rocks.  The  inclosing  rocks  are  penetrated 
by  narrow  dikes  of  the  aphanitic  dacite-porphyry.  The  aphanitic  modifica- 
tion (93)  has  very  much  the  same  microstructure  as  that  near  the  contact 
north  of  Echo  Peak,  except  for  abundant  small  feldspars,  which  are 
larger  than  the  constituents  of  the  groundmass.  They  are  only  sparingly 
present  in  the  case  of  the  other  locality.  Parts  of  this  contact  zone  are 
aphanitic,  with  irregularly  stellate  or  dendritic  spots  (90).  The  micro- 
structure  is  rather  panidiomorphic,  with  distinct  quartz  crystals,  and  the 
dark-colored  spots  are  biotite  and  muscovite  and  alteration  products,  now 
mostly  iron  oxide,  probably  derived  from  biotite.    The  mica,  when  unal- 


BIGHORN  PASS  SHEET.  69 

tered,  extends  tliroug-h  the  grouiidinass  for  some  distance  as  single  crystals, 
inclosing  many  quartz  crystals,  in  a  ])oikilitic  manner. 

Tlie  same  kind  of"  contact  zone  exists  east  of  Mount  Holmes  and  west 
of  Trilobite  Point.  The  plane  of  contact  is  nearly  vertical,  and  from  the 
ai)hanitic  marginal  zone  numerous  offshoots  penetrate  the  adjacent  rocks. 
The  dikes  are  white,  aphanitic,  and  exhibit  banding  and  flow  structure. 
Specimens  from  the  contact  were  studied  and  found  to  be  very  fine  grained, 
with  micropoikilitic  structure,  the  quartz  individuals  being  about  0.15  mm. 
in  diameter,  and  having  a  skeleton-like  form,  the  outline  of  each  quartz 
being  nearly  idiomorphic,  but  not  continuous,  as  .shown  in  PI.  XI,  fig.  4. 
The  feldspar  forms  minute  clouded  grains  and  crystals.  There  are  micro- 
scopic flakes  of  muscovite  scattered  through  the  rock,  and  some  calcite.  In 
the  bysmalith  rock  immediately  in  contact  with  the  andesite-porphyrv  of 
the  laccolith  the  microscopic  skeleton  quartzes  are  scattered  in  a  micro- 
cryptocrystalline  groundmass.  Calcite  is  abundant  in  irregular  grains. 
The  aphanitic  rock  penetrates  the  limestone  in  sheets  that  sometimes  break 
into  thin  crumpled  layers.  This  modification  is  microgranular,  very  fine 
grained,  and  not  poikilitic,  and  consists  of  quartz  and  feldspar  in  allotrio- 
morphic  grains.  The  size  of  the  grains  varies  slightly  in  alternate  layers, 
producing  the  lamination.  Minute  flakes  of  muscovite  are  scattered  through 
the  rock  and  intersect  one  another  at  all  angles.  They  are  more  abundant 
in  some  layers  than  in  others. 

Similar  offshoots  of  microgranular  rock  occur  on  the  north  side  of 
Panther  Creek  and  near  the  ridge  west  of  the  head  of  Gallatin  River.  In 
these  bodies,  however,  biotite  is  more  abundant,  and  the  micropoikilitic 
structure  passes  into  micrographic  structure  as  the  feldspar  inclosures 
assume  a  more  uniform  orientation  (96,  97,  98). 

BIGHORN  PASS  SHEET. 
KERSANTITE. 

The  small  obscure  body  of  dark-colored  porphyry-like  rock  which  is 
exposed  in  the  vicinity  of  Bighorn  Pass  is  characterized  by  phenocrysts  of 
hornblende  and  mica,  and  rarely  those  of  feldspar.  In  places  the  horn- 
blendes are  quite  large  ;  in  other  parts  of  the  mass  there  are  no  phenocrysts 
(124).  On  the  pass  the  sheet  is  from  50  to  75  feet  thick.  On  the  north 
side  of  Three  River  Peak  there  is  a  nearly  horizontal  intrusive  sheet,  10  feet 


70 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 


thick,  of  dense  aphanitic  gray  and  red  rock  (100),  which  might  be  mistaken 
at  first  2-lance  for  a  fine-g-rained  sandstone.  It  is  at  about  the  same  horizon 
as  the  sheet  at  Bighorn  Pass,  and  proves  to  be  of  similar  rock.  Its 
resemblance  to  this  rock  was  not  recognized  in  the  field,  and  though  associ- 
ated with  dikes  of  dacite-porphyry  its  relation  to  them  was  not  noted. 

Under  the  microscope  the  rock  from  Bighorn  Pass  is  seen  to  consist  of 
a  holocrystalline  groundmass  of  feldspar,  mostly  plagioclase,  with  quartz 
and  some  orthoclase,  and  larger  crystals  of  augite,  biotite,  and  occasional 
hornblende,  with  abundant  magnetite,  besides  chlorite  and  calcite.  It  is 
not  fresh,  the  augite  and  hornblende  being  partly  decomposed.  Its  chemical 
composition  is  as  follows: 

Analysis  of  J^ersantite  from  Bighorn  Pass. 

[Analyst,  J.  E.  Whitfield.] 


Constituent. 


SiO-,.. 

TiOi  . 

Al.Oa. 

Fe,0., 

FeC. 

MnO. 

MgO  . 

CaC. 

SrO.- 

BaO.. 

Li,0  . 

NajO. 

K:0.. 

P2O,.. 

SO3  .. 

CI.... 

CO,  .. 

H20.. 


1. 


liBss  O  for  CI . 


48.73 

1.34 

11.92 

4.79 

4.56 

.36 

5.93 

9.24 

None. 

Trace. 

Trace. 

2.62 

2.47 

.32 

.34 

.11 

5.80 

1.52 


47.73 


100. 05 
.02 


10.07 
7.39 
4.29 
.23 
7.66 
6.97 


3.78 
1.22 


49.82 


14.  50 
8.06 


5.81 
7.69 


3.03 
3.50 

Trace. 

Trace. 


0.88 
4.46 


4.42 
2.54 


99.68 


99.37 


100. 03 


i 


1  =  Kersantite,  Bighorn  Pass. 

2  =  Minette,  Eiobelberg,  Heidelberg.' 

3^Ker8antite,  between  Falkenstein  and  Steinbacb  Miihle,  Fichtelgebirge.^ 


'  From  Roth's  Tables  of  chemical  analyses,  Beitr:ige  zur  Petrographie  der  plutonischen  Gesteine, 
4°,  Berlin,  1873,  xxvi. 
•^  Ibid,  1884,  xxiv. 


BIGHORN  PASS  SHEET.  71 

The  high  percentage  of  carbon  dioxide,  5.80,  corresponds  to  the 
abundance  of  calcito.  The  comparatively  low  alumina  and  relatively  high 
alkalies  are  noteworthy.  The  potash  is  comparatively  high  for  so  basic  a 
rock,  and  accounts  for  the  j)resence  of  abundant  biotite.  Magnesia  is  below 
the  normal  ])ercentage  for  a  rock  with  so  little  silica.  It  has  entered  into 
the  composition  of  biotite,  malacolite,  and  hornblende.  No  orthorhombic 
pyroxene  or  olivine  has  been  developed.  A  comparison  of  this  rock  with 
several  others  somewhat  similar  in  chemical  composition  will  be  made 
later  on. 

The  microscopic  feldspars  are  polysynthetic  twins  of  lime-soda  feldspar, 
with  high  extinction  angles,  corresponding  to  labradorite.  They  are  nearly 
idiomorphic,  rectangular  to  lath-shaped  crystals,  of  pure  substance,  and 
when  not  obscured  by  calcite  they  appear  perfectly  fresh  and  not  at  all 
crushed.  It  seems  as  though  the  calcite  had  been  derived  from  other 
sources — that  is,  from  the  pyroxene,  or  by  infiltration  from  the  inclosing 
limestone.  The  absence  of  strain  or  crushing  is  significant  in  connection 
with  the  proximity  of  this  thin  .sheet  to  the  massive  laccolith,  and  indicates 
that  this  lamprophyric  rock  is  the  more  recent  intrusion.  In  places  the 
form  of  the  feldspar  is  tabular.  And  sometimes  the  rectangular  crystals 
are  bounded  by  a  margin  of  unstriated  feldspar  with  allotriomorphic  out- 
line, and  in  some  cases  idiomorphic  outline.  This  feldspar  has  a  lower 
index  of  refraction  than  that  of  the  inclosed  feldspar,  and  is  undoubtedly 
orthoclase.  Its  mode  of  occurrence  is  precisely  the  same  as  that  of  the 
orthoclase  in  the  groundmass  of  the  basaltic  rocks,  absarokite  and  shosho- 
nite,  described  in  Chapter  IX.  Grains  of  quartz  constitute  the  last  crystal- 
lization of  the  groundmass.  It  is  probable,  however,  that  some  of  the 
quartz  is  secondary,  since  it  occurs  in  idiomorphic  crystals  surrounded  by 
calcite.  There  are  many  grains  and  crystals  of  magnetite  and  abundant 
minute  hexagonal  prisms  of  colorless  apatite.  Brown  biotite  is  in  part 
idiomorphic,  in  part  allotriomorphic,  with  penetrations  of  plagioclase  and 
inclusions  of  apatite  and  magnetite.  The  monoclinic  pyroxene,  with  large 
angle  of  extinction  and  rather  low  double  refraction,  is  almost  colorless  in 
thin  section,  and  is  a  diopside  or  malacolite.  It  is  partly  altered  along 
cracks  and  around  the  margin,  with  the  formation  of  calcite  and  chlorite.  It 
is  mostly  idiomorphic,  in  comparatively  large  crystals,  and  does  not  occur 
in  microlites  in  the  groundmass.     The  crystals  have  the  ordinary  form  and 


72      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

distinct  prismatic  cleavage.  Inclusions  of  magnetite  occur.  The  pyroxene 
appears  to  have  been  an  earlier  crystallization  than  the  biotite.  Hornblende, 
which  is  the  most  prominent  constituent  in  some  forms  of  the  rock,  is  hardly 
seen  in  the  thin  sections  prepared.  It  occurs  to  only  a  small  extent  in 
microscopic  crystals. 

In  the  finer-grained  modifications  of  the  rock  the  porphyritical  charac- 
ter of  the  pyroxene  becomes  more  pronounced.  The  groundmass  consists  of 
allotriomorphic  feldspars,  with  scattered  lath-shaped  crystals  of  jjlagioclase, 
apparently  belonging  to  the  more  calcic  varieties,  together  with  magnetite 
or  apatite;  biotite  is  partly  in  microscopic  individuals,  partly  in  megascopic 
ones.  There  are  also  microscopic  grains  and  crystals  of  calcite  and  patches 
of  chlorite.  In  these  varieties  the  pyroxene  is  wholly  altered  to  chlorite  or 
serpentine. 

In  a  marginal  modification  of  the  rock,  without  phenocrysts,  the  crystal- 
lization of  the  groundmass  is  very  fine  grained,  and  the  original  structure 
is  greatl.y  obscured  by  secondary  biotite  in  microscopic  plates,  which  project 
into  aggregates  of  quartz.  This  quartz  exhibits  peculiar  interference  phe- 
nomena, suggesting  polysynthetic  twinning. 

The  mineral  composition  of  the  rock,  as  well  as  the  chemical,  is  unusual. 
They  both  correspond  somewhat  closely  to  certain  kersantites  and  minettes, 
analyses  of  one  of  each  of  which  are  placed  in  columns  by  the  side  of  the 
analysis  of  this  rock  for  comparison.  It  is  to  be  remarked  that  the  minette, 
according  to  analysis,  contains  less  potash  than  the  kersantite.  There  is,  in 
fact,  nothing  in  the  chemical  composition  to  suggest  the  crystallization  of 
orthoclase  feldspar.  But  this  is  equally  the  case  in  the  rock,  leucite- 
absarokite,  from  Ishawooa  Canyon,  whose  analysis  is  given  in  Chapter 
IX,  and  in  which  the  feldspathic  constituents  are  orthoclase  and  leucite. 
Several  analogous  magmas  form  dikes  in  the  vicinity  of  the  Crandall 
volcano  (Chapter  VII).  They  are  somewhat  richer  in  magnesia  and  potash, 
and  are  characterized  by  olivine,  biotite,  and  orthoclase  feldspar.  As  in 
their  cases,  this  unusual  magma  is  known  only  in  a  small  mass.  Mineral- 
ogicaUy  it  may  be  classed  with  kersantites,  although  it  bears  a  certain 
resemblance  to  absarokite. 


INTRUSIVE  KOCKS  OF  THE  GALLATIN  MOUNTAINS.  73 

GRAY  MOUNTAIN  1HA8S  AND  CONNECTED  SHEETS. 

The  igneous  mass  of  Gray  Mountain  and  Joseph  Peak,  with  the  intru- 
sive sheets  directly  connected  with  it,  consists  of  andesite-porphyry  and 
holocrystaUine  andesites,  having  a  considerable  range  of  composition.  The 
greater  portion  is  hornblende-mica-andesite-porphyry ;  a  considerable  part  is 
hornblende-andesite-porphyry,  and  a  small  part  is  hornblende-pyroxene,  or 
pyroxene-audesite-porphyry,  while  some  varieties  might  be  classed  as  dacite. 
The  numerous  bodies  examined  exhibit  a  variation  in  the  mineral  composi- 
tion, even  within  some  of  the  bodies  of  small  size,  especially  with  reference 
to  the  relative  proportions  of  phenocrysts  of  hornblende  and  biotite.  So 
that  hornblende-mica-andesite-porphyries  are  in  some  places  richer  in  mica 
than  in  others,  or  richer  in  hornblende.  There  is  also  a  variation  in  the 
amount  of  dark-colored  minerals  ])resent.  Some  are  rich  in  ferromagnesian 
silicates ;  others  poor  in  them.  The  latter  are  richer  in  feldspar  and  in  ground- 
mass,  and  are  usually  lighter  colored.  In  general,  it  is  found  that  in  the 
vai'ieties  with  comparatively  few  ferromagnesian  silicates  biotite  is  in  excess 
of  hornblende,  but  not  always.  In  those  richer  in  these  minerals  hornblende 
preponderates  over  biotite  in  most  cases,  but  not  in  all.  There  is  conse- 
quently a  transition  in  varieties  from  those  rich  in  hornblende  with  little  or 
no  biotite  to  those  containing  biotite  with  little  or  no  hornblende.  The 
last-named  variety,  however,  does  not  constitute  any  considerable  body. 
Only  a  very  few  carry  quartz  phenocrysts,  but  quartz  is  a  microscopic 
constituent  of  the  groundraass  in  all  the  more  crystalline  varieties,  so  that 
the  classification  of  any  of  the  rocks  as  dacite  must  rest  upon  a  chemical 
basis. 

HORNBLENDE-MICA-ANDESITE-PORPHYRY  AND  ANDESITE. 

The  main  mass  of  the  intrusion  is  hornblende-mica-andesite-porphyry. 
It  is  a  light-gray  rock,  with  abundant  small  phenocrysts  of  feldspar,  horn- 
blende, and  biotite,  the  groundmass  being  aphanitic.  It  is  compact,  with 
an  even  to  hackly  fracture,  cracking  into  slabs  and  angular  fragments.  It 
resembles  the  Indian  Creek  laccolith  very  closely  (146,  147,  170). 

The  forty-five  thin  sections  representing  these  hornblende-mica-andesite- 
porphyries  resemble  one  another  in  so  many  respects  that  their  microscopical 
characteristics  may  be  described  collectively.  The  constituent  minerals 
being  alike  in  nearly  all  cases,  the  difference  between  the  various  rock 
bodies  lies  in  the  crystallization  of  the  groundmass. 


74  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

In  only  a  few  of  the' rocks  are  all  of  the  rain"erals  unaltered,  or  nearly 
fresh.  In  most  cases  the  hornblende  is  completely  decomposed,  while 
biotite  is  generally  unaltered  in  most  of  them.  The  feldspars  are  unaltered 
in  nearly  all  the  rocks  examined.  The  least  altered  rocks  were  found  in 
the  Gray  Mountain  mass  (146,  147),  in  a  heavy  sheet  in  the  g-ulch  on  the 
sovithwest  slope  of  Electric  Peak  (191),  and  in  the  sheet  forming  the  western 
summit  of  Electric  Peak  (197).  In  these  bodies  the  hornblende  is  almost 
entirely  fresh. 

The  hornblende  is  greenish  brown  with  the  usual  pleoclu'oism,  between 
dai-k  greenish  brown  and  light  brown.  In  some  cases  a  zonal  structure  is 
exhibited,  the  zones  being  different  shades  of  the  same  color.  In  other 
cases,  notably  in  a  segregation  of  hornblende,  the  color  is  chestnut  brown 
to  purplish  brown,  jiassing  into  greenish  brown,  and  into  green  at  the 
margin,  the  zonal  arrangement  of  the  colors  not  being  parallel  to  crystal- 
lographic  forms,  but  irregular.  In  some  individuals  the  margin  is  reddish 
brown.  These  tones  also  occur  in  phenocrysts  in  the  groundmass  that 
incloses  the  segregations  of  hornblende.  This  particular  rock  is  rich  in 
hornblende  and  poor  in  biotite,  and  appears  to  be  a  less  siliceous  variety. 
In  the  more  siliceous  varieties  of  these  rocks  the  hornblende  has  more  of 
the  greenish  tone.  The  shape  of  its  crystal  is  that  common  to  these  kinds 
of  rocks — short,  stout  prisms,  generally  idiomorphic.  Cleavage  and  twin- 
ning are  also  normal.  The  substance  of  the  unaltered  hornblende  is  quite 
pure,  there  being  but  few  inclusions,  usually  magnetite.  It  occasionally 
surrounds  biotite  and  augite  (164)  as  nearly  synchronous  crystallizations, 
each  being  allotriomorphic  with  respect  to  the  other.  Sometimes  there  is  a 
border  of  minute  biotite  plates  surrounding  the  hornblende  (146).  Decom- 
position begins  as  chloritization  around  the  margin  of  the  hornblende  and 
along  cracks.  When  completely  altered,  there  is  a  pseudomorph  consisting 
of  chlorite  with  grains  of  iron  oxide,  and  areas  or  cores  of  calcite,  and 
sometimes  muscovite  in  confused  aggregations.  The  latter  mineral  appears 
to  have  been  derived  from  the  biotite  in  the  rock,  which  is  also  decomposed 
in  such  cases  (201).  In  an  upturned  sheet  of  andesite-jiorphyry  in  the 
southeast  spur  of  Electric  Peak  the  hornblende  phenocrysts  have  been 
converted  into  nearly  parallel  aggregates  of  actinolite  (222).  In  the  rock 
on  the  south  slope  of  Gray  ]\Iountain,  where  it  appears  to  be  somewhat 
coarser  grained  and  more  easily  eroded  (148),  the   hornblende,   in  part 


GRAY  MOUNTAIN  MASS  AND  CONNECTED  SHEETS.  75 

chloritized,  is  more  or  less  wholly  replaced  by  a  zeolite,  which  from  its 
optical  behavior  seems  to  be  scolecite. 

Biotite  occurs  in  rather  thick  six-sided  crystals,  often  idioinorph'c.  The 
color  is  brown,  with  strong'  absorption.  Inclusions  are  not  frequent,  being 
magnetite  and  apatite,  rarely  zircon.  In  some  places  lenticular  layers  of  cal- 
cite  have  been  deposited  along  cleavage  planes  in  the  biotite,  distorting  the 
laraelliie.  Decomposition  results  in  the  formation  of  chlorite  and  epidote, 
and  sometimes  of  muscovite. 

Feldspar  phenocrysts  are  abundant  in  most  of  the  rocks,  but  not  in  all. 
In  only  a  few  cases  are  they  unaltered;  in  general  they  are  clouded  with 
more  or  less  secondary  material.  They  are  all  plagioclase;  the  unaltered 
ones  in  the  less  siliceous  rocks  are  in  part  labradorite.  In  other  cases  they 
appear  to  be  andesine-oligoclase.  Zonal  structure  is  pronounced.  In  some 
of  the  less  altered  feldspars  minute  cracks,  which  are  evidently  the  result  of 
crushing,  traverse  the  crystals  in  crudely  parallel  directions,  and  have  led 
to  the  production  of  secondary  minerals  of  several  kinds.  One  is  colorless, 
with  lower  refraction  than  feldspar,  but  nearly  the  same  double  refraction. 
It  occurs  in  patches,  with  sharp-pointed  edges.  Another  is  colorless,  with 
higher  refraction  and  stronger  double  refraction  than  feldspar.  Its  identity 
was  not  made  out.  Other  secondary  minerals  replacing-  feldspar  are  calcite, 
epidote,  and  a  microcryptocrystalline  aggregate  which  is  indeterminable. 
In  one  instance  (148)  the  same  zeolite  replaces  feldspar  which  replaces 
hornblende. 

Quartz  occurs  as  phenocrysts  in  only  a  few  cases  (147,  198).  It  forms 
small  rounded  crystals,  with  occasional  inclusions  of  other  minerals.  Mag- 
netite in  small  grains  may  be  reckoned  with  the  phenocrysts.  Apatite,  and 
rarely  zircon,  also  belong  to  the  crystals  first  formed. 

The  groundmass  of  these  hornblende-mica-andesite-porphyries  is  holo- 
crystalline  and  exceedingly  fine  grained.  No  specimen  of  the  central  part 
of  the  Gray  Mountain  mass  was  collected,  hence  its  coarsest  crystallization 
is  not  known.  Nothing  was  seen  that  indicated  a  coarser  grain  than  exists 
in  the  Indian  Creek  laccolith.  The  specimens  collected  are  from  the  marginal 
portion.  Of  these,  the  coarsest  grained  is  micropoikilitic  and  finer  grained 
than  the  coarsest-grained  variety  of  the  Indian  Creek  laccolith.  This  grades 
into  modifications  with  less  pronounced  micropoikilitic  structure  (146,  147, 
148).     The  constituents  of  the  groundmass  are  rectangular  and  lath-shaped 


76      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

feldspars  with  low  extinction  angles.  Some  exhibit  no  twinning.  It  is 
probable  that  oligoclase  and  orthoclase  are  both  present.  Irregularly  shaped 
grains  also  occur.  Quartz  is  present  as  poikilitic  cement,  or  in  minute  grains 
when  this  structure  is  not  developed.  Magnetite  crystals  and  some  irregular 
shreds  of  biotite  and  green  hornblende  also  take  part  in  the  groundmass. 
In  this  mass  lie  small  crystals  of  feldspar  and  the  fen-omagnesian  minerals, 
varying  in  size  to  the  largest  phenocrysts.  In  one  specimen  small  quartz 
plienocrysts  occur  (1-47).  The  groundmass  of  the  rock  forming  the  western 
summit  of  Electric  Peak  is  micropoikilitic,  with  more  liornl^lende  and  biotite 
as  constituents  (197).  The  same  structure  is  found  in  an  altered  sheet  on 
the  northeast  spur  of  this  mountain  ("214).  Slightly  finer-grained  forms  of 
this  same  structure  occur  in  two  other  sheets  in  Electric  Peak  (201,  151). 
A  lower  grade  of  crystallization  has  smaller  and  less  distinctly  poikilitic 
grains,  with  clearly  defined  lath-shaped  feldspars  that  sometimes  exhibit  a 
fluidal  arrangement.  A  still  lower  grade  consists  of  minute  lath-shaped 
feldspars,  with  indistinct  patches  of  poikilitic  quartz,  and  spots  that  are 
microcryptocrystalliue.  There  is  sometimes  pronounced  flo^v  structure. 
In  thin  sections  the  groundmass  is  gray,  with  minute  feldspars,  and  mag- 
netite grains,  and  occasional  apatites.  These  modifications  are  but  slightly 
different  from  audesites,  and  might  be  classed  as  such.  They  occur  in 
varieties  richer  in  biotite  than  in  hornblende.  A  microstructure  very  similar 
to  this,  but  less  uniformly  developed  and  still  finer  grained,  is  found  in  a 
crushed  sheet  in  the  southeast  spur  of  Electric  Peak  (213),  where  the  rock 
is  considerably  altered.  In  this  case  it  is  possible  that  the  micropoikilitic 
structure  is  secondary.  The  lowest  grade  of  crystallization  allied  to  the 
micropoikilitic  is  one  in  which  there  is  a  brownish  base,  which  is  doubtfully 
holocrystalline.  In  this  are  feldspar  microlites  and  irregular  grains,  in 
places  approaching  a  poikilitic  structure.  It  is  probable  that  the  rock  is 
holocrystalline.     Its  habit  is  thoroughly  andesitic. 

The  microstinicture  of  other  modifications  of  these  intrusive  sheets  is  not 
very  different  from  the  micropoikilitic  varieties,  in  that  it  consists  of  lath- 
shaped  feldspars  and  grains  of  feldspar  and  quartz  of  nearly  the  same  size 
as  in  the  other  cases,  but  the  poikilitic  cementing  quartz  is  wanting.  These 
rocks  are  very  fine  grained,  the  average  diameter  of  the  grains  being  about 
0.02mm.,  or  smaller.  In  one  instance  the  granular  groundmass  is  filled  with 
phenocrysts  of  feldspars  and  some  micrographic  intergrowth  smrounding 


IFTKDSIVE  SHEETS  IN  GALLATIN  MOUNTAINS.  77 

the  smaller  crystals  (210).     A  granular  microcrystalline  to  microcrypto- 
crystalline  structure  occurs  :u  some  of  the  sheets. 

Another  class  of  microstructures  is  that  in  which  the  groundmass  con- 
sists of  grains  and  crudely  idiomorphic  crystals  of  feldspar  and  quartz,  with 
abundant  small  crystals  of  quartz,  nearly  idiomorphic,  in  six-sided  pyramids, 
generally  inclosing  several  grains  of  feldspar.  The  structure  may  grade 
into  micropoikilitic.  In  the  best-developed  groundmass  of  this  kind,  in 
andesite-porpln'ry  from  the  ridge  north  of  Fawn  Pass  (1-iO),  the  quartz 
crystals  are  0.3mm.  in  length  and  smaller.  The  rock  is  rich  in  biotite  and 
poor  in  hornblende.  In  other  cases  the  grain  is  smaller,  and  innumerable 
idiomorphic  quartzes,  0.01  in  diameter,  fill  the  groundmass.  This  structure 
is  developed  in  the  sheet  of  andesite-porphyry,  rich  in  hornblende  (191), 
which  occurs  in  the  gulch  southwest  of  the  summit  of  Electric  Peak.  In  a 
few  cases  the  lath-shaped  feldspars  preponderate  over  the  granular  minerals, 
giving  the  groundmass  a  holocrystalline  pilotaxitic  structure. 

HORNBLENDE-ANDESITE-PORPHYRY  AND  ANDESITE. 

Of  the  remaining  intrusive  sheets  in  this  part  of  the  Grallatin  Moun- 
tains very  much  the  greater  number  are  hornblende-andesite-porphyries  and 
holocrystalline  andesites  without  pyroxene  and  without  biotite,  except  a 
trace  in  some  instances.  A  very  few  bodies  contain  pyroxene,  either  with 
hornblende  or  without. 

In  contrast  to  the  hornblende-mica-audesite-porphyiies  the  hornblende- 
andesite-porphyries  are  less  decomposed,  the  hornblende  being  only  partly 
altered  in  most  cases,  and  qviite  fresh  in  a  number  of  instances.  This  is  the 
more  noteworthy  since  they  appear  to  be  older  than  the  hornblende-mica 
rock  in  several  instances,  though  not  in  all.  The  hornblende-andesite- 
porphyries  and  andesites  are  characterized  by  abundant  small  phenocrysts 
of  hornblende  and  fewer  of  feldspar.  They  vary  in  amount  of  phenocrysts 
and  in  the  general  color  and  habit  of  the  rock.  Some  are  scarcely  dis- 
tinguishable from  the  hornblende-mica  rocks  into  which  they  grade.  The 
hornblende  phenocrysts  have  the  same  habit  and  colors,  brownish  green, 
with  reddish-brown  tones  in  places,  and  upon  alteration  are  replaced  by 
chlorite  or  calcite,  or  both  together,  sometimes  with  grains  of  epidote  or 
titanite.  The  feldspar  phenocrysts  are  plagioclase,  apparently  andesine- 
labradorite,  with  zonal  structure  and  twinning,  as  in  the  rocks  just  described. 


78  GEOLOGY  OF  THE  YELLOWSTONE  NATlOJfAL  PAKK. 

They  are  much  less  abundant  and  smaller  in  most  of  the  present  group, 
and  are  in  part  cracked  and  altered  in  the  same  manner  as  in  the  hornblende- 
mica  rocks.  In  some  instances  the  feldspar  is  perfectly  fresh  when  the 
hornblende  is  entirely  altered,  and  vice  versa.  The  only  other  constituent 
that  may  be  classed  with  the  phenocrysts  is  maguetite,  in  small  crystals, 
scattered  through  the  rock,  and  inclosed  in  the  hornblende.  It  is  in  some 
cases  decomposed  and  replaced  by  aggregations  of  hydrous  oxide  of  iron, 
leucoxene,  and  brightly  polarized  scales  of  an  undetermined  mineral.  The 
magnetite  is  plainly  titaniferous,  and  chemical  analysis  shows  1.71  per  cent 
of  titanium  oxide  in  the  rock  analyzed      Pyrite  is  occasionally  present. 

The  groundmass,  always  holocrystalline,  consists  in  most  cases  of  a 
microcrystalline  aggregation  of  grains  that  are  indistinctly  poikilitic,  and 
of  feldspar  microlites,  both  lath-shaped  and  rectangular,  together  with 
magnetite  and  irregularly  shaped  hornblende  or  chlorite.  In  one  case  the 
micropoikilitic  structure  is  more  pronounced.  In  others  the  lath-shaped 
and  rectangular  feldspars  preponderate.  In  two  instances  the  gi-oundmass 
is  microcryptocrystalline,  with  scattered  feldspar  microlites  and  some  indis- 
tinct micropoikilitic  structure. 

On  the  ridge  running  southwest  from  Electric  Peak  three  distinct 
bodies  of  intrusive  rock  intersect  one  another.  The  oldest  is  a  somewhat 
altered  hornblende-andesite-porphyry  (185).  This  is  traversed  by  a  large 
sheet  of  hornblende-andesite-porphyry,  which  is  quite  fresh,  light  gray 
colored,  with  abundant  small  phenocrysts  of  hornblende  and  feldspar. 
Through  the  rock  are  segregations,  several  inches  in  diameter,  that  differ 
greatly  in  texture  and  structure.  Some  appear  as  coarser-grained  modifi- 
cations of  the  main  rock,  others  as  varieties  with  larger  hornblende.  Some 
have  a  laminated  or  gneissoid  structure.  Occasionally  small  dark  patches 
surround  red  garnets  (182,  184,  188,  189).  The  main  body  of  the  rock, 
whose  chemical  composition  is  given  in  analysis  1,  p.  81,  consists  of  a 
micropoikilitic  groundmass,  with  abundant  lath-shaped  and  rectangular 
feldspars,  Ijesides  hornblende,  a  little  chlorite,  magnetite,  and  quartz,  carry- 
ing phenocrysts  of  hornblende  and  cracked  plagioclase.  It  is  remarkable 
that  by  the  side  of  greatly  cracked  crystals  of  plagioclase,  with  the  cracks 
filled  with  the  secondary  mineral  already  described,  the  crystals  of  horn- 
blende exhibit  no  cracking,  often  no  cleavage,  and  no  optical  strain 
phenomena.     The  question  arises  whether  or  no  the  cracking  of  the  feld- 


INTRUSIVE  SHEETS  IN  GALLATIN  MOUNTAINS.  79 

spar  was  produced  by  dynamic  forces  actin<];-  on  the  whole  rock.  The 
nearly  parallel  position  of  the  cracks  in  all  feldsj)ars  in  one  rock  section 
indicates  that  it  was  due  to  such  action.  The  total  absence  of  cracking  in 
the  hornblende  and  the  very  fresh  condition  of  this  mineral  are  certainly 
remarkable  (li^-)-  In  one  instance,  where  a  large  hornblende  is  adjacent 
to  a  feldspar,  both  are  cracked  in  the  same  direction,  but  the  hornblende 
exhibits  no  alteration  along  the  cracks.  The  alteration  within  the  feldspar 
appears  to  be  confined  entirely  to  its  crystal,  and  to  depend  upon  the 
feldspar  substance,  and  not  to  be  in  the  nature  of  an  infiltration  which 
might  have  lodged  within  the  cracks  in  the  hornblende.  At  the  margin  of 
the  I'ock  body  the  color  is  dark  and  the  phenocrysts  are  very  small  and  in 
greater  numbers  (184).  The  groundmass  is  microcryptocrystalliiie,  with 
indistinct  poikilitic  patches.  In  other  parts  of  the  body  the  groundmass 
has  a  microgranular  structure  with  minute  idiomorphic  quartzes.  This  is 
in  contact  with  one  of  the  segregations  (188),  which  consists  of  an  aggre- 
gate of  rectangular  feldspars,  for  the  most  pai't  in  polysynthetic  twins  with 
low  extinction  angles,  and  of  larger  hornblendes,  with  a  small  amount  of 
interstitial  cement  of  feldspar  and  quartz  grains.  It  contains  long,  slender 
needles  of  apatite,  pailially  altered  magnetite,  and  some  chlorite  in  flakes, 
which  suggest  former  biotite.  The  hornblende  is  precisely  the  same  as 
that  in  the  surrounding  rock,  and  the  segregation  is  plainly  a  local  modifi- 
cation of  the  magma  of  the  rock.  One  segregation  consists  wholly  of 
brownish-green  hornblende.  Another  segregation  consists  of  similar  horn- 
blende crystals  crowded  together,  with  rather  large  feldspars,  and  no  fine- 
grained cement.  There  is  some  quartz,  calcite,  and  chlorite.  The  feldspars 
are  more  or  less  altered,  while  the  hornblende  is  perfectly  fresh.  The 
banded  segregations  with  gneissoid  appearance  consist  of  plagioclase  and 
hornblende,  with  biotite  in  places,  considerable  magnetite  and  green  spinel, 
besides  chlorite  as  an  alteration  of  biotite.  There  is  little  or  no  quartz. 
The  banded  structure  is  due  to  the  arrangement  of  magnetite,  spinel,  and 
biotite  in  streaks  or  layers,  and  to  the  crystallization  of  part  of  the  feld- 
spar in  small  crystals  and  grains  in  layers.  While  the  dark-colored  miner- 
als exhibit  a  pronounced  parallel  arrangement  in  places,  the  crystals  of 
feldspar  lie  in  all  possible  positions,  and  share  in  the  banded  character  only 
by  being  in  small  grains  or  in  large  crystals.  The  hornblendes  and  some 
biotites  are  poikilitic,  inclosing  small  rounded  crystals  of  plagioclase.     The 


80  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAHK. 

end  of  a  large  hornblende  is  normally  developed  where  it  lies  within  the 
groundmass  of  the  rock,  but  within  the  banded  segregation  it  is  poikilitic, 
and  is  traversed  by  a  broad  band  of  feldspar  grains.  In  places  where  the 
banding  of  the  magnetite  and  biotite  is  most  pronounced  and  is  in  delicate 
lines,  the  feldspars  are  comparatively  large  and  cross  the  lines  of  magnetite 
at  all  angles  without  modifying  them.  The  lamination  was  earlier  than 
the  crystallization  of  the  feldspars.  It  did  not  affect  the  orientation  of  the 
hornblende  material.  It  must  have  preceded  the  crystallization  of  the 
hornblende.  It  atfected  the  size  of  the  feldspar  crystals  in  part.  The  size 
of  crystals  depends  primarily  upon  the  rate  of  cooling  or  upon  the  viscosity 
of  the  magma.  Since  the  cooling  must  have  been  the  same  for  all  parts  of 
so  small  a  mass,  the  most  variable  factor  is  likely  to  have  been  the  viscosity, 
which  depends  not  only  on  the  temperature  but  on  the  chemical  composi- 
tion. Hence  we  may  conclude  that  heterogeneity  in  the  mass  must  have 
been  the  cause  of  the  banding  and  abnormal  microstructm-e  in  these  small 
gneiss-like  segregations. 

HORNBLENDE-PYROXENE-ANDESITE-PORPHYRIES  AND  ANDESITES. 

The  hornblende-pyroxene-andesite-porphyries  and  andesites  are  few  in 
number  and  are  closely  associated  with  the  hornblende  rocks.  One  forms 
a  narrow  sheet  on  the  ridge  north  of  the  head  of  Fan  Creek  (162,  167).  It 
is  dense  and  andesitic  in  appearance,  with  hornblende  phenocrysts.  The 
groundmass  is  holocrystalline  and  pilotaxitic,  with  abundant  magnetite. 
Part  of  the  rock  has  small  phenocrysts  of  augite  in  addition  to  those  of 
hornblende,  besides  numei'ous  small  augites,  first  recognized  under  the 
microscope.     The  groundmass  is  more  coarsely  crystallized. 

Two  other  modifications  occur,  whose  character  is  in  doubt,  owing  to 
the  complete  decomposition  of  the  ferromagnesian  constituents.  They  were 
probably  pyroxene  rocks  (131, 132,  134,  136).  They  are  both  fine  grained, 
without  phenocrysts.  Their  general  mineral  composition  is  similar  to 
that  of  the  rocks  already  described.  Their  microstructure  is  andesitic, 
approaching  a  microlitic  and  glassy  structure.  Some  of  the  pseudomorphs 
have  the  shape  of  olivine,  and  it  is  possible  that  one  of  these  rocks  is  an 
altered  basalt  or  olivine-andesite. 


INTRUSIVE  SHEETS  IN  GALLATIN  MOUNTAINS. 


81 


CHEMICAL  COMPOSITION. 

Of  the  rocks  belonging  to  this  intrusive  mass  and  its  outlying  slieets 
tlu'ee  have  been  analyzed  chemically,  and  their  analyses  are  given  in  the 
accompanying  table.  No.  1  is  from  a  sheet  on  the  ridge  southwest  of  the 
summit  of  Electric  Peak  (182),  and  is  honiblende-andesite-porphyry.  No. 
2  is  the  rock  forming  tlie  thick  sheet  between  Fan  Creek  and  Cinnabar 
Creek  (164),  and  is  hornblende-mica-andesite-porphyry.  No.  3  is  from  the 
southern  slope  of  Gray  Mountain,  and  is  jiart  of  the  great  intrusive  mass 
(146);  this  also  is  hornblende-raica-andesite- porphyry. 

Analyses  of  rocks  from  vicinity  of  Electric  Peakj  Fan  Creelc,  and  Gray  Mountain. 

[Aii.alyst,  J.  E.  ■\VliitlieId.l 


Constituent. 

1. 

2. 

3. 

SiO, 

58.49 

05.63 

65.64 

TiO, 

1.71 

Trace. 

None. 

A1-0-, 

16.70 
8.85 

17.00 
2.55 

17.29 
3.07 

Fe;0;, 

FeO 

2.37 

1.19 

1.29 

MnO 

.24 

Trace. 

MgO 

3.12 

2.03 

1.78 

CaO 

5.90 

3.48 

1.98 

Li.,0                        

.01 

3.47 

1.59 

Trace. 

.04 
4.42 
1.64 

.07 

.04 
5.77 
2.44 

.23 

Na.O 

K.O 

P.O.. 

SO, 

.63 

Trace. 

Trace. 

CO. 

.27 

Trace. 

HO 

2.44 

2.00 

1.03 

Total 

100.  52 

100.  32 

100.  73 

From  these  analyses  it  is  seen  that  the  hornblende-andesite-porphyry 
has  3  per  cent  less  silica  than  the  hornblende-mica  rock  of  the  Indian  Creek 
laccolith  with  nearly  the  same  alkalies,  and  that  the  former  has  more  mag- 
nesia and  considerable  titanium  oxide.  The  hornblende-mica-andesite- 
porphyries  of  the  Gray  Mountain  system  which  were  analyzed  have  more 
silica  than  the  Indian  Creek  laccolith,  and  somewhat  more  alkalies  and  less 
lime.  Chemically  and  mineralogically  they  are  near  dacites,  and  might  be 
classed  with  them.     Some  of  the  rocks  contain  abundant  idiomorphic  quartz 


82      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

in  microscopic  plienocrysts,  and  are  undoubtedly  dacite.  No  attempt  has 
been  made  to  distinguish  on  the  map  the  different  kinds  of  rocks  forming' 
the  larg-e  mass  and  intrusive  sheets  just  described. 

DIFFERENTIATED   SHEET   SOUTHEAST   OF  Er,ECTRIC  PEAK. 

One  intrusive  sheet  occurs  in  the  upturned  shales  of  the  southeastern 
spur  of  Electric  Peak  which  deserves  special  mention.  It  is  about  30  feet 
thick,  and  at  present  stands  in  a  nearly  vertical  position,  as  do  the  inclosing- 
.shales.  It  is  notable  on  account  of  its  composition  and  the  strongly  con- 
trasted character  of  the  lower  and  upper  parts  of  the  sheet.  The  rock  is 
massive  and  greenish  near  the  eastern  wall,  which  was  originally  the  bottom 
surface;  it  is  fissile  and  ci'umbles  upon  weathering-,  giving  rise  to  a  narrow 
gulch.  Immediately  in  contact  with  the  shale  it  is  dense,  with  a  purplish 
tinge.  A  layer  of  the  sheet,  4  or  5  feet  thick,  near  what  was  the  bottom,  is 
full  of  large  porphyritical  augites  (225,  228).  The  i-emainder  of  the  sheet 
does  not  contain  tliem,  except  sporadically,  and  carries  small  feldspar  plie- 
nocrysts. It  is  more  massive,  and  weathers  quite  differently  from  the 
coarsely  porphyritic  part.  From  the  abundance  of  large  augite  crystals  in 
the  bottom  portion  of  the  sheet  it  appears  that  these  ciystals  must  have 
settled  to  the  lower  part  while  the  magma  was  quite  liquid,  a  phenomenon 
not  observed  in  any  other  rocks  of  this  region,  where  the  })henocrysts  are 
uniformly  disseminated  through  the  rock.  Such  separations  by  gravity 
have  been  uoted  by  Charles  Darwin^  in  the  basalt  lavas  of  the  Gralapagos 
Islands,  and  by  Clarence  King"  in  the  basalt  flows  of  Hawaii.  In  each  of 
these  cases  the  rocks  in  which  this  phenomenon  has  been  observed  are 
basic,  as  is  the  intrusive  sheet  in  question.  A  high  degree  of  liquidity  after 
the  phenocrysts  have  been  formed  seems  to  be  a  necessary  condition,  and 
is  one  most  likely  to  occur  in  basic  rocks. 

The  chemical  composition  of  the  two  parts  of  the  sheet  is  shown  by 
the  following  analyses.  No.  1  is  of  the  lower  portion,  crowded  with  large 
augite  crystals,  the  layer  being  about  one-sixth  of  the  total  depth  of  the 
sheet;  No.  2  is  of  the  more  feldspathic  portion;  No.  3  is  tlie  average 
composition  of  the  sheet,  reckoning  the  parts  analyzed  in  the  proportion  of 
1  to  5. 

'  Volcauio  Islands,  London,  1851,  p.  117. 

*  U.  S.  Geol.  Expl.  Fortieth  Par.,  Vol.  I,  Systematic  Geology,  p.  715. 


UIFFEKKNTIATE])  INTRUSIVE  SHEET. 


83 


Analyses  of  different  parts  of  the  sheet  southeant  of  Electric  Peak, 


CoDstitnent. 

1. 

2. 

8. 

SiO- 

50. 59 

.80 

11.  .53 

1.83 

7.64 

.06 

.17 

11.27 

8.79 

.10 

.03 

2.27 

2.33 

Trace. 

.48 

Trace. 

None. 

.21 

1.76 

52.10 
.79 

16.34 
3.84 
6.82 

51.85 

.79 

15.  .54 

3.50 

6.95 

.01 

.03 

5.49 

5.40 

.01 

Trace. 

3.73 

3.89 

.10 

.64 

.20 

.18 

1.78 

Ti(t    

Al  0, 

Fo->0 1             

KeO 

NiO 

MnO 

MgO 

CaO 

Trace. 
4.33 
4.73 

BaO 

SrO 

Na:0 

K;0 

Li,0 

4.02 
4.20 
.13 
■  68 
.24 
.22 

[      1.74 

PjO, 

CI 

SOi 

HjO  below  110'^ 

H-O  above  110"  

Total 

99.86 

100. 18 
.05 

100.  09 
.04 

Less  0  for  CI 

' 

100. 13 

100.  05 

The  cliemical  composition  of  the  sheet  is  not  hke  that  of  any  of  the 
igneous  rocks  of  Electric  Peak  and  Sepulchre  Mountain,  being-  lower  in 
silica  and  proportionately  higher  in  alkalies.  It  approaches  the  composition 
of  shoshonite  (Chapter  IX),  and  indicates  that  the  magma  is  a  more  highly 
differentiated  form  of  the  general  magma.  The  two  parts  of  the  sheet  cor- 
respond in  chemical  composition  more  closely  to  absarokite  and  shoshonite 
(q.  v.),  and  are  the  results  of  a  differentiation  in  which  the  separation  was 
according  to  mineral  molecules,  as  it  was  actually  the  settling  of  pyroxene 
crystals.  The  ratio  of  the  alkalies  to  one  another  in  the  two  parts  is  nearly 
constant,  indicating  that  they  remained  in  combination. 

The  u^iper  part  of  the  rock,  10  feet  from  the  top,  consists  of  feldspar, 
most  of  which  is  plagioclase,  and  is  striated.  It  is  partly  in  tabular  or 
equidimensional  crystals,  with  allotriomorphic  outlines,  partl}^  in  lath-shaped 
and  rectangular  crystals,  more  nearly  idiomorphic  and  generally  of  smaller 
size.     The  extinction  angles  are  low,  often  nearly  zero,  indicating  oligoclase. 


84      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Some  of  the  feldspars  exhibit  no  poly  synthetic  twinning  and  have  low 
extinction  angles,  and  are  probably  orthoclase.  The  substance  of  the  feld- 
spar is  clouded  by  minute  secondary  grains.  There  is  also  considerable 
colorless  malacolite  or  diojjside  in  small  irregular  crystals  and  in  short  stout 
prisms,  besides  partly  altered  magnetite  and  abundant  long  needles  of 
apatite;  also  abundant  green  and  brown  secondary  mineral  in  irregular 
aggregations,  which  in  places  resembles  microcryptocrystalline  aggregates 
of  chlorite  or  serpentine,  and  in  other  places  appears  to  be  microscopic 
crystals  of  brown  mica.  Biotite  is  also  sparingly  present  in  long  shreds  or 
crooked  plates  and  in  stout  crystals.  About  10  feet  from  the  bottom  of  the 
sheet  the  lath-shaped  feldspars  are  more  abundant,  long  prismatic  crystals  of 
malacolite  are  numerous,  and  magnetite  or  ilmenite  occurs  in  small  grains 
and  in  greater  numbers.  There  are  some  porphj-ritical  malacolites  and 
felds])ars,  besides  patches  of  brightly  polarizing  micro-fibrous  material  with 
larger  needles  of  actinolite  scattered  through  it. 

The  portion  of  the  rock  filled  with  large  malacolite  crystals  consists  of 
these  large  crystals,  more  or  less  idiomorphic  in  outline,  in  a  subordinate 
amount  of  feldspar  matrix,  composed  of  lath-shaped  feldspars,  like  those 
already  described,  besides  small  crystals  of  malacolite  and  iron  oxide. 
There  is  nnich  actinolite  in  thin  needles,  and  in  a  greenish,  microscopic  felt, 
which  is  bright  green  or  pleochroic  in  some  places  and  colorless  in  others. 
Around  the  grains  of  magnetite  the  felt  is  colored  brown.  The  large  mala- 
colites are  to  some  extent  altered  to  fibers  of  actinolite  that  lie  parallel  to 
the  prismatic  axis  of  the  pyroxene.  It  is  a  question  whether  the  patches  of 
actinolite  felt  may  not  be  altered  olivine.  This  seems  probable  from  the 
shajje  of  some  of  them,  but  no  unaltered  olivine  is  observed  in  the  thin 
sections  of  the  rock. 

GAIiLiATIN  RIVER  liACCOLITH. 

DACITE-PORPHYRY. 

In  connection  with  the  iutnisive  bodies  in  the  Gallatin  Movmtains 
should  be  mentioned  a  laccolith-like  mass  situated  on  the  Grallatin  River  just 
west  of  the  l^order  of  the  Yellowstone  Park.  It  is  within  and  near  the  base 
of  the  Paleozoic  strata.  The  rock  is  a  dacite-porphyry  with  prominent  pheno- 
cr5rsts  of  feldspar  and  abundant  smaller  ones  of  hornblende,  besides  small 
rounded  crystals  of  quartz.     In  thin  sections  the  large  feldspars  are  seen  to 


INTRUSIVE  SHEEia  IN  MOUNT  EVERTS.  85 

be  andesine-labradorite  with  marked  zonal  structure,  and  with  cracking-  and 
secondary  inchisions  simihir  to  those  in  the  andesite-porphyries  ot"  this 
rejifion.  Thecjuartz  crystals  are  sometimes  idiomori)hic  pyramids,  or  are 
nearly  spherical,  or  are  irregularly  shaped.  They  contain  bays  and 
inclusions  of  groundmass  and  many  liquid  inclusions  with  cubes  and  gas 
bubbles ;  rhombohedral  cleavage  is  occasionally  developed.  The  hornblende 
is  green  and  more  or  less  chloritized.  A  few  crystals  of  biotite  and  of 
sphene  were  noticed.  Magnetite  occurs  in  small  individuals,  and  colorless 
apatite  in  comparatively  large  ones.  AUanite  is  present  in  brown  jileochroic 
crystals,  witli  idiomorphic  form  and  zonal  structure.  Strongly  pleochroic 
epidote  in  irregular  grains  is  sparingly  present  as  a  secondary  mineral. 
The  groundmass  is  fine  grained,  microgranular,  with  minute  idiomorphic 
quartzes  and  abundant  crystals  of  magnetite  (168,  169). 

INTRUSIVE  SHEETS  IX  MOUNT  E^^BTS. 

There  are  a  number  of  intruded  sheets  of  igneous  rock  within  the 
Cretaceous  strata  of  Mount  Everts,  the  lowest  being  exposed  near  the  base 
of  the  south  side  of  the  mountain,  and  the  highest  at  the  top  of  the  west 
escarpment.  The  rocks  as  a  group  are  dark  greenish  and  brownish  grays 
to  slate  color.  They  are  dense  and  aphanitic  to  very  fine  grained,  and  for 
the  most  part  are  free  from  prominent  phenocrysts.  The  rocks  are  altered 
holocrystalliue  andesites  and  andesite-porphyries. 

The  coarsest-gi'ained  form  occurs  in  a  sheet  20  to  30  feet  thick  at  the 
base  of  the  south  face  of  the  mountain  (365).  The  rock  is  greatly  fractured, 
with  joints  along  which  there  has  been  sliding  about  parallel  to  the  bedding 
of  the  inclosing  sedimentary  strata.  It  consists  of  nearly  idiomorphic  lime- 
soda  feldspars,  with  low  extinction  angles  and  low  dovible  refraction,  about 
0.4  mm.  long,  the  marginal  part  being  unstriated  and  cloudy.  A  few  are 
phenocrysts  2  mm.  long.  There  is  considerable  serpentine  and  a  little  pale- 
green  augite  not  yet  altered.  Magnetite  occurs  in  small  crj'stals,  and 
colorless  apatite  is  abundant  in  minute  thin  prisms.  Numerous  shreds  of 
red-brown  biotite  may  be  secondary.  The  rock  is  a  pj-roxene-andesite- 
porphyry. 

In  the  west  escarpment  several  thin  sheets  were  observed  by  Mr. 
Wright.  They  are  aphanitic  and  porphyritic  (356,  357),  with  phenocrysts 
of  feldspar  and  decomposed  pyroxene.  The  feldspar  is  parti}'  altered,  and 
is  probably  labradorite.     The  groundmass  is  extremely  fine  grained  and  is 


86      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

comjjosed  of  pi'isms  of  plag-ioclase,  much  serpeutiue  or  chlorite,  and  altered 
magnetite,  wliich  is  now  light  yellow  by  incident  light.  There  are  sugges- 
tions of  crystals  of  pyroxene,  now  altered.  The  structure  is  andesitic  and 
the  rocks  are  holocrystalline  pyroxene-andesites.  There  is  much  calcite 
scattered  through  the  rocks. 

The  intrusive  sheet  near  the  top  of  the  northern  part  of  the  west 
escarpment,  which  can  be  distinguished  even  at  a  long  distance  from  the 
inclosing  sand.stones,  because  of  its  dark  color,  is  about  20  or  30  feet  thick 
in  places,  but  much  thinner  in  others.  It  lies  parallel  to  the  bedding  of  the 
strata,  except  for  short  distances,  where  it  breaks  across  the  beds.  In 
])laces  it  exhibits  prismatic  parting  at  right  angles  to  the  contact  surfaces, 
and  in  other  places  the  spheroidal  suiidering  is  well  developed.  The  rock  is 
dark  and  dense,  with  few  phenocrysts  of  hornblende  (360,  361,  362).  It 
contains  segregations  of  hornblende.  The  same  sheet  of  rock  is  exposed 
lower  down  the  northwest  spur  of  the  mountain,  near  the  line  of 
the  forty-fourth  parallel  of  latitude  (363,  359).  It  is  a  holocrystalline 
pyroxene-andesite,  or  pyroxene-andesite-porphyry,  carrying  a  small  amount 
of  hornblende.  Its  habit  is  like  that  of  similar  andesites  of  Sepulchre 
Moimtain,  there  being  innumerable  small  phenocrysts  of  labradorite  and 
pyroxene  in  a  groundmass  of  still  smaller  crystals  of  the  same  minerals, 
with  magnetite  and  some  micropoikilitic  quartz.  The  rock  is  considerably 
decomposed  in  part,  the  pyroxenes  having  suffered  most.  Portions  of  it 
contain  fresh  augite  and  altered  hypersthene.  The  hornblende  is  brown, 
with  a  border  of  magnetite  and  pyroxene.  Near  the  contact  planes  of  the 
sheet  the  groundmass  of  the  rock  is  still  finer  grained. 

These  rocks  are  similar  to  the  intruded  sheets  in  the  Cretaceous  strata 
of  Electric  Peak,  and  it  is  possible  that  they  may  have  been  connected 
with  them  before  the  faulting  of  the  region  by  the  great  north-south  faults 
on  both  sides  of  Sepulchre  Mountain. 

THE  BinVSEK  PEAK  MASS. 
DACITE-PORPHYRY. 

The  Bunsen  Peak  mass  is  an  intrusive  body  that  broke  through  Creta- 
ceous strata,  which  are  exposed  in  contact  with  it  on  the  Gardiner  River 
near  the  mouth  of  Glen  Creek,  and  which  dip  away  from  it  northward  at  an 
angle  of  10°.  Erosion  has  removed  the  sedimentary  covering,  leaving  an 
isolated,  dome-like  mountain,  whose  base  has  been  surrounded  on  all  sides  by 


THE  BUNSEN  PEAK  MASS, 


87 


streams  of  rliyolitir  and  basaltic  lavas.  The  rock  is  litrlit  gray  and  fine 
grained,  with  abnndant  small  phenocrysts  of  feldspar  and  biotite.  It  is  a 
mica-dacite-i)t)rphyry,  \vlu)se  chemical  comjjosition  is  as  follows: 


A  nalysia  of  Bunsen  Peak 

micadacite-porphyry. 

Constituent. 

(102) 

SiO. 

70.52 

Trace. 

15. 85 

2.28 

.36 

.09 

.09 

2.59 

Trace. 

.3.93 

3.43 

.17 

.29 

.35 

TiO. 

ALO, 

FeO, 

FeO 

MnO 

MgO 

CaO 

Li,0 

Na^O 

K.O 

P.Os 

SO, 

HO 

Total 

99.95 

This  analysis  was  made  from  the  rock  at  the  summit  of  Bunsen  Peak. 
It  is  nearly  the  same  as  that  of  the  rock  from  Mount  Holmes  (p.  65),  beino- 
a  little  lower  in  alumina  and  higher  in  lime  and  potash. 

The  mineral  composition  and  microstructure  of  the  rock  vary  but 
slightly  throughout  the  body.  Under  the  microscope  it  is  seen  to  consist 
of  a  holocrystalline  groundmass  of  feldspar  and  quartz,  with  abundant  flakes 
of  biotite  and  a  little  magnetite  Small  crystals  of  apatite  and  minute 
prisms  of  zircon  are  present.  There  are  numerous  phenocrysts  of  irregularly 
outlined  biotite,  idiomorphic  feldspar,  and  a  few  corroded  crystals  of  quartz. 
The  feldspar  phenocrysts  are  almost  all  polysynthetic  twins  of  lime-soda 
feldspars,  oligoclase-andesine,  also  twinned  according  to  the  Carlsbad  law, 
and  having  marked  zonal  structure.  A  few  appear  to  be  labradorite.  Some 
unstriated  feldspars  may  be  orthoclase.  They  have  few  inclusions,  and 
exhibit  very  little  decomposition  in  some  parts  of  the  rock.  The  cracking 
and  secondary  minerals  characteristic  of  the  feldspar  phenocrysts  in  the 
intrusive  rocks  of  the  Gallatin  Mountains  also  occur  in  parts  of  this  rock. 
The  biotite  is  brown,  with  strong  absorption  and  few  inclusions.  It  is  for 
the  most  part  unaltered.     Quartz  phenocrysts  are  much  corroded  and  carry 


88  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

few  inclusions.  They  are  scarce  in  most  sections  of  the  rock,  and  are  more 
numerous  in  the  linest-gi'ained  portions  at  the  northeastern  extension  of  the 
mass.  The  groundmass  in  the  coarsest-grained  forms,  which  occur  about 
the  middle  of  the  northern  and  western  sides  of  the  mountain,  is  micro- 
crystalline,  and  consists  of  lath-shaped  and  rectangular  feldspars  and  micro- 
poikilitic  quartzes,  about  O.Oo  mm.  in  diameter  and  smaller,  with  some 
magnetite  crystals  and  a  few  flakes  of  biotite.  The  microstructure  is 
shown  in  PI.  XIX,  fig.  1.  The  poikilitic  quartzes  are  more  pronounced 
in  some  parts  of  the  rock  than  in  others,  and  exhibit  a  tendency  toward 
idiomorphism  (105,  106,  108).  The  same  structure  occurs  in  smaller  grain 
at  the  summit  of  the  mountain,  on  its  southeastern  face,  and  at  its  uortliern 
base,  where  the  rock  is  exposed  in  knolls  near  Grardiner  River  and  elsewhere. 
Where  the  dacite-porphyry  comes  in  contact  with  a  large  mass  of  sandstone, 
probably  included  within  the  igneous  mass,  the  porphyrj-  exhibits  platy  part- 
ing pai'allel  to  the  plane  of  contact,  which  disappears  a  short  distance  away. 
The  microstructure  of  the  rock  near  the  contact  is  indistinctly  micropoiki- 
litic,  the  quartz  patches  being  very  minute.  In  spots  it  is  microcryptocrys- 
talline.  The  finest-grained  forms  occurring  near  the  contact  with  sedimentary 
rocks  on  Gardiner  River  below  the  mouth  of  Glen  Creek,  and  in  the  spur 
of  the  plateau  west,  are  microgranular,  with  minute  idiomorphic  quartzes, 
averaging  0.01  nun.  in  diameter. 

A  coarse-grained  mass  resembling  granite  occurs  in  the  base  of  the 
clifi^  on  the  northern  side  of  the  mountain,  and  consists  of  quartz,  feldspar, 
and  biotite,  with  the  grain  of  fairly  coarse  granite.  It  is  a  crystallization 
from  the  same  magma  as  the  dacite-porphyry,  for  the  crystals  of  feldspar 
along  its  margin  project  into  the  porphyry  groundmass  with  idiomorphic 
outline.  It  is  not  a  broken  fragment  of  some  foreign  rock  inclosed  during 
the  eruption  of  the  porphyry.  Tlie  mineral  constituents  are  the  same  as 
those  of  the  porphyry,  both  in  kind  and  in  general  character.  The  biotite 
has  the  same  color  and  has  similar  inclusions  of  magnetite.  The  feldspars 
are  orthoclase  and  oligoclase,  with  some  crystals  of  andesine-labi'adorite. 
The  quartz  is  allotriomorphic  with  respect  to  all  the  other  minerals,  and 
contains  gas  inclusions,  with  a  small  amount  of  liquid.  Magnetite,  apatite, 
and  zircon  occur  as  in  granite.  This  is  clearly  a  coarse-grained  crystalliza- 
tion of  the  magma,  due  to  some  cause  not  known,  and  presents  the  true 
granite  equivalent  of  the  dacite-porphyry.  Similar  coarse-grained  masses 
occur  in  the  dacite-porphyry  of  the  Holmes  bysmalith,  near  Echo  Peak. 


CHAPTER    III. 

THE  IGNEOUS  ROCKS  OF  ELECTRIC  PEAK  AND  SEPULCHRE 

MOUNTAIN. 


By  Joseph  Paxson  Iddings. 


GEOLOGICAL  SKETCH  OF  THE  REGION. 

As  already  stated  in  Chapter  II,  the  series  of  eruptions  that  broke 
through  the  synclinal  fissure  in  what  is  now  the  eastern  part  of  Electric 
Peak  are  so  plainly  related  to  the  lavas  that  form  the  volcanic  pile  of 
Sepulchre  Mountain  and  the  foothills  at  its  southwestern  base,  and  the 
character  of  this  relationship  is  of  siich  petrographical  importance,  that 
these  rocks  will  be  treated  conjointly.^  It  has  been  shown  that  the  erap- 
tions  that  accompanied  the  synclinal  folding  and  Assuring'  in  the  eastern 
part  of  Electric  Peak  were  subsequent  to  the  intrusion  of  the  sheets  of 
andesite-porphyry  between  the  beds  of  shale  and  sandstone. 

The  general  character  and  form  of  Electric  Peak  are  exhibited  in  the 
accompanying  map  and  illustrations.  The  Peak  is  the  highest  point  in 
the  Gallatin  Mountains,  being  11,100  feet  in  altitude,  and  is  situated  upon 
the  northern  boundary  of  the  Yellowstone  Park,  the  forty-fifth  parallel  of 
latitude  passing  just  south  of  the  summit.  For  this  reason  it  is  not  well 
shown  on  either  of  the  atlas  sheets  north  or  south  of  this  parallel.  The 
accompanying  map  (PL  XVI)  shows  its  relation  to  Sepulchre  Mountain,  as 
well  as  its  geological  structure,  which  has  been  explained  on  pages  50  to  55, 
where  the  character  of  the  sedimentary  formations  and  their  position  and 
the  nature  of  the  intruded  sheets  of  andesite-porphyry  were  described. 

The  sharply  pointed  peak  has  broad,  steep  slopes  on  the  west  and 
south,  where  streams  have  cut  3,000  feet  below  the  summit  of  the  mountain. 

■  Iddings,  J.  P.,  The  eruptive  rocks  of  Electric  Peak  iiud  Sepulchre  Mountain,  Yellowstone 
National  Park:  Twelfth  Ann.  Kept.  U.  S.  Geol.  Survey,  1892,  pp.  569-664. 

89 


90      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

A  narrow  spur  or  ridge  connects  the  peak  with  the  mountains  to  the  south- 
west, while  a  broad,  high  ridge  on  the  north  carries  the  gently  dipping 
Cretaceous  strata  to  the  abrupt  synclinal  fold  south  of  Cinnabar  Mountain. 
On  the  east  and  northeast  of  the  summit  deep  gulches  have  been  carved 
into  the  heart  of  the  inass,  reaching  depths  of  -4,000  and  5,000  feet  below 
its  highest  point.  The  valley  of  Reese  Creek  marks  the  line  of  faulting 
between  Electric  Peak  and  Sepulchre  Mountain. 

Only  the  eastern  half  of  Electric  Peak  is  involved  in  the  consideration 
of  the  series  of  volcanic  eruptions  here  discussed,  the  central  stock  or 
conduit  of  eruption  being  located  in  the  middle  of  the  deep  gulch  east  of 
the  peak  and  in  the  rocky  spur  north  of  the  gulch,  and  the  apophyses  and 
dikes  extending  only  short  distances  across  the  southeastern  and  north- 
eastern spurs.  The  accompanying  view  of  the  eastern  face  of  the  mountain 
(PI.  XIII)  shows  the  jagged  northeastern  spur  on  the  right,  with  its  steeply 
sloping  base,  and  the  deep  east  gulch  in  the  middle,  with  light-colored 
morainal  accumulations  of  rock  fragments  covering  the  bottom  like  a  glacier. 
The  long  southeastern  spur  is  on  the  left,  with  its  short,  steep  branch  imme- 
diately south  of  the  gulch.  The  barren  slopes,  partly  covered  with  slide- 
rock,  are  easily  recognized. 

The  southeastern  spur  is  formed  of  upturned  beds  east  of  the  synclinal 
axis.  The  black  shales  which  constitute  the  greater  part  of  the  spur  have 
been  baked  and  indurated  in  the  vicinity  of  the  stock,  so  that  tliey 
have  withstood  erosion  sufficiently  to  form  the  pyramidal  mass  bounding 
the  east  gulch  on  the  south.  The  main  mass  of  Electric  Peak  and  the 
greater  portion  of  the  northeast  s^Dur  consist  of  less  disturbed  strata  dipping 
toward  the  northeast.  The  structure  of  the  mountain  is  shown  in  the  walls 
of  the  deep  gulches  draining  east  and  northeast,  as  well  as  in  the  bare 
slopes  on  the  south  and  west  sides.  The  differences  in  the  topography  of 
the  two  halves  of  the  mountain  are  due  to  the  influence  of  the  vertically 
intruded  rocks,  which  have  metamorphosed  the  neighboring  sandstones  and 
shales,  i-endering  them  hard  and  resisting,  and  leading  to  the  production  of 
rugged  and  pinnacled  ridges,  Avith  precipitous  walls  hundreds  of  feet  in 
height. 

The  east  gulch  forms  an  amphitheater  at  the  base  of  the  peak,  which 
surmounts  a  precipice  of  nearly  1,500  feet.  The  walls  of  this  amphitheater 
are  shown  in  the  panorama,  PI.  XIV.  The  gulch  crosses  the  synclinal  axis 
and  the  stock  of  igneous  rock,  part  of  which  is  covered  by  debris.     The  can- 


13 


U.  8.   GEOLOGICAL  6URVEV 


MONOGRAPH  XXXII      PART  It      PL.   XIII 


-^^■r^.'^^P^ 


ELECTRIC   PEAK,   FROM  SEhuLCHRE   MOUNTAIN- 


14 


U.  a.  QEOLOOICAL  euOvEv 


MON00P*PH  X)(!C(I 


HEAD  OF  EAST  GULCH   OF  ELECTRIC  PEAK. 


ELKCTRIC  PEAK  AND  SKPdLOHRB  MOUNTAIN.  1)1 

Tral  portion  of  tlie  stock  is  located  on  the  northeastern  s])ur  of  the  mountain, 
where  it  is  surrounded  by  sandstones.  It  is  well  ex])Osed  throug-h  a  vertical 
distance  of  a  thousand  feet.  \  large  a])0])hysis  extends  up  the  crest  of  this 
spur,  forniiufi-  dark-colored  pinnacles,  shown  on  tlie  right-hand  side  of  the 
panorama.  The  southwestern  end  of  the  stock  is  ex])osed  in  the  southern 
wall  of  the  ani}ihitheater  (left  side  of  the  panorama).  It  is  a  high  wedge 
of  crystalline  rock,  reaching  to  within  a  few  hundred  feet  of  the  top  of  the 
cliff.  The  crest  of  the  southeastern  spur,  from  an  altitude  of  10,000  feet 
to  the  summit  of  the  peak,  is  serrated  by  numerous  narrow  gulches  and 
rocky  points,  caused  by  the  unequal  weathering  of  dikes  and  of  upturned 
intrusive  sheets.  The  nearly  vertical  dikes  are  frequent  between  the 
wedge  of  crystalline  rock  and  the  fault  to  the  west.  They  become  fewer 
toward  the  summit  of  the  peak  and  do  not  occur  farther  northwest.  They 
extend  across  the  southeastern  spui",  appearing  on  its  southern  slope  in  Avails 
rising  above  the  black  shales.  They  do  not  occiu*  at  the  eastern  base  of 
the  spur.  Where  dikes  and  upturned  intrusive  sheets  are  parallel  it  is 
difficult  to  distinguish  them  from  one  another.  The  sheets,  however,  usually 
exhibit  signs  of  crushing  and  displacement.  The  dikes  are  more  numerous 
and  thicker  nearer  the  area  of  metamorphism.  They  are  not  more  than  a 
mile  and  a  half  long,  and  radiate  from  a  center  on  the  northeastern  spui', 
which  is  about  the  location  of  the  stock.  They  range  thr(jngh  45°  from 
south  to  southwest. 

Sepulchre  Mountain,  east  of  the  great  fault,  located  near  the  line  of 
Reese  Creek,  consists  of  andesitic  tuff-breccia.  With  this  mass  of  breccia, 
which  also  forms  the  low  ridge  south  of  the  mountain,  is  associated  a  set 
of  dikes  and  broad  intrusive  bodies  that  have  broken  up  through  the  breccia. 
The  breccia  is  3,000  feet  thick,  and  rests  upon  Cretaceous  and  older  strata 
exposed  along  the  northern  and  eastern  bases  of  the  mountain.  It  is  well 
exposed  in  bold  escarpments  on  the  northern  side  of  the  mountain,  the 
southern  and  southwestern  sides  being  smooth,  glaciated  slopes  with  few 
outcrops.  The  contrast  between  the  northern  and  southern  sides  of  the 
mountain  is  shown  in  PI.  XV,  the  view  having  been  photographed  from  the 
northwestern  spur,  looking  southeast. 

The  breccias  are  but  crudely  bedded;  in  places  not  bedded  at  all.  With 
them  are  a  few  massive  lava  streams.  The  whole  mass  is  distinctly  a' olcanic. 
The  dikes  in  the  western  part  trend  mostly  in  a  north  and  northeasterly 
direction,  radiating  from  the  vicinity  of  Cache  Lake.     A  few  trend  east. 


92      GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

It  is  probable  that,  instead  of  the  broad  bodies  of  intrusive  andesite  and 
dacite  represented  on  the  map,  there  are  a  number  of  smaller  bodies  of 
similar  rocks  intersecting  one  another,  but  the  data  at  hand  are  iusuflftcient 
to  enable  their  more  accurate  representation. 

In  the  northwestern  spur  of  the  mountain  the  dikes  are  well  marked, 
from  5  to  25  feet  wide,  and  not  perfectly  straight.  Some  of  the  intrusive 
bodies  carry  inclosed  masses  and  small  fragments  of  black  shale,  and  where 
the  fault  plane  traverses  the  massive  igneous  rock  the  latter  has  been  crushed 
into  angular  fragments,  which  are  cemented  together  by  particles  of  the 
same  rock,  producing  a  crushed  breccia,  somewhat  resembling  the  tutf- 
breccia. 

The  rhyolite  that  occurs  over  the  breccia  in  Glen  Creek  Valley  is  part 
of  the  great  rhyolite  sheet,  and  is  of  much  more  recent  date,  following  the 
faulting  and  erosion  (if  the  Electric  Peak  and  Sepulchre  Mountain  masses. 

The  accompanying  map  (PI.  XVI)  shows  in  a  simple  manner  the  chief 
geological  features  of  a  limited  area  embracing  the  rocks  to  be  described. 
The  sedimentary  terranes  are  colored  according  to  the  period  in  which  they 
were  formed,  embracing  the  Carboniferous,  Juratrias,  and  Cretaceous. 
The  sheets  of  igneous  rocks  intruded  between  the  strata  are  not  drawn 
continuous,  as  they  exist,  owing  to  the  fact  that  the  data  are  insufficient. 
They  are  more  numerous  than  represented  on  the  map,  and  are  thinner. 
The  same  is  true  of  the  dikes. 

Although  the  two  mountains  were  at  one  time  geologically  connected 
and  the  eruptive  rocks  were  in  a  sense  a  geological  vmit,  it  will  be  conven- 
ient and  profitable  to  describe  them  separately  at  first,  and  afterwards  to 
consider  their  correlation. 

THE  INTRUSIVE  ROCKS  IN  ELECTRIC  PEAK. 

The  intrusive  rocks  in  Electric  Peak,  west  of  the  fault,  occurring  in 
the  stock  and  its  apophyses  and  in  dikes,  form  a  group  of  diorites  and 
diorite-  and  andesite-porphyries  of  variable  composition  and  structure. 
They  grade  into  one  another  Ijy  transitions  in  composition  and  structure. 
The  coarse-o-rained  granular  rocks — diorites — occur  almost  wholly  within 
the  stock  and  its  larger  apophyses,  while  the  finer-grained  porphyritic 
rocks — porphyries — occur  in  the  dikes  and  smaller  apophyses,  and  in  places 
along  the  margin  of  the  stock,  in  contact  with  sedimentary-  rocks. 

The  greater  part  of  the  stock  is  diorite,  which  varies  in  structure  and 


INTRUSIVE  ROOKS  IN  ELECTRIC  PEAK,  93 

composition,  in  some  places  rapidly  aiul  (juite  irregulai'ly.  Moroovei',  there 
are  abundant  evidences  of  the  successive  eruption  throuoh  the  fissure  or 
conduit  of  different  molten  magmas.  The  porphyries  also  differ  from  the 
main  body  of  diorite  in  the  character  of  their  pheuocrysts — that  is,  in  those 
minerals  which  were  present  in  the  magma  when  it  came  to  rest.  Most  of 
the  porphyries  contain  phenocrysts  of  hornblende  and  biotite,  but  none 
of  p-\'roxene.  In  some  of  the  diorites  there  was  an  early  crystallization  of 
brown  hornblende  and  of  pyroxene,  but  none  of  biotite.  In  most  of  the 
diorites  there  is  no  evidence  of  any  development  of  phenocrysts.  They 
were  magmas  free  from  crystals  at  the  time  of  their  eruption. 

In  order  to  understand  the  relation  of  the  various  dikes  to  the  stock 
rocks,  let  us  consider  the  possible  course  of  events  that  would  follow  a 
synclinal  Assuring  of  sedimentary  sti'ata  when  the  dynamical  action  was 
repeated  and  when  igneous  magmas  were  forced  up  through  the  cracks. 
Evidently  the  first  magma  would  penetrate  all  the  small  crevices  connected 
with  the  larger  fissures  and  fill  them  with  its  material,  which  would  solidify 
rapidly  as  narrow  dikes.  The  magma  in  the  large  fissure  would  remain 
molten  much  longer,  consolidation  setting  in  along  the  sides  and  in  the 
narrow  portions.  A  subsequent  eruption  would  force  out  the  molten  por- 
tion and  replace  it  by  other  material.  It  would  fill  any  new  crevices  made 
at  the  time  of  its  eruption.  The  number  of  such  crevices  would  probably 
be  smaller  toward  the  end  of  the  series  of  eruptions  than  at  the  beginning. 
Hence  the  number  of  dikes  of  the  later  magmas  would  be  smaller.  The 
magma  that  closed  the  conduit  would  in  such  a  case  be  represented  by 
few  dikes.  If  the  final  action  was  a  violent  explosion,  the  reverse  would 
be  true.  At  Electric  Peak  the  final  eruption  was  comparatively  weak,  and 
is  represented  by  a  small  body  of  quartz-diorite-porphyry  within  the  stock 
and  in  six  or  eight  narrow  dikes  trending  southwest. 

These  rocks  form  a  very  complex  group,  so  intimately  connected 
geologically  and  exhibiting  such  gradual  transitions  in  composition  and 
structure  from  one  extreme  to  another  that  there  appears  to  be  no  simple 
method  of  describing  them  or  of  discussing  their  various  relationships.  For 
convenience  of  petrographical  description  they  will  be  treated  in  the  follow- 
ing groups : . 

I.  The  greater  number  of  dike  rocks  and  some  of  the  contact  forms  of 
the  stock,  probably  older  than  the  main  body  of  the  stock. 


94 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


II.  The  main  body  of  the  stock,  most  of  its  contact  forms,  and  most 
of  the  rocks  that  have  broken  through  it,  with  some  apojihyses,  probably 
contemporaneous  with  the  main  mass. 

III.  The  quartz-mica-diorite-porphyry  that  broke  through  the  stock 
and  also  produced  some  dikes. 

I.  THE  DIKE  ROCKS  AND  CERTAIN  CONTACT  FORMS  OF  THE  STOCK. 

Porphyries. — The  porpliyrics  forming  most  of  the  dikes,  which  are  from 
1  to  25  feet  in  width,  have  a  g-enerally  uniform  habit.  They  are  dense 
and  aphanitie,  filled  with  small  phenocrysts  of  feldspar  and  ferromagnesian 
silicates,  mostly  hornblende  and  biotite.  They  have  a  uniformly  speckled 
appearance,  with  occasional  spots  of  white  feldspar  or  black  ferromagnesian 
silicates.  Variations  in  habit  are  due  to  differences  in  color,  caused  b}'  the 
relative  propoi'tions  of  light  and  dark  colored  phenocrysts,  and  to  the  nature 
and  amount  of  the  groundmass.  The  color  varies  from  dark  greenish  and 
purplish  gray  to  light  gray  of  different  tints.  The  dike  rocks  are  in  some 
cases  fresh  and  compact,  in  others  decomposed  and  disintegrated. 

In  thin  sections  under  the  microscope  the  groundmass  of  all  these  dike 
rocks  is  found  to  be  holocrystalline,  and  the  phenocrysts  are  lime-soda  feld- 
spar and  hornblende,  generally  with  biotite,  occasionally  with  pyroxene. 
The  relative  proportions  of  these  minerals  vary  gradually  among  the  rock 
bodies,  so  that  the  specimens  collected  may  be  arranged  in  the  follow- 
ing subdivisions,  according  to  the  relative  amounts  of  the  ferromagnesian 
silicates : 

Table  I. — Mineral  variatioH  of  the  andesite-porphyries  of  Electric  Peak. 


Besides  the   phenocrysts  of  biotite  there  are  shreds   of  this  mineral 
that  belong  to  the  period  of  crystallization  of  the  groundmass.     There  is  a 


DIKE  ROCKS  OF  ELECTRIC  PEAK.  95 

gTiulual  variation  iu  the  kiiuU  ot  lime-soda  t'eldspjir  accoinjjaiiyiuy  that  ot 
the  lerroiuagnesian  minerals.  But  transitions  in  the  possible  isomorphous 
series  of  hornblendes  or  pyi'oxenes  were  not  detected.  The  variation  iu  min- 
eral composition  affects  the  microstructure  of  the  groundmass,  an  inci'ease 
of  quartz  being-  accompanied  by  an  approach  to  a  granular  structure. 

Altliouffli  the  coarseness  of  jjrain  and  at  the  same  time  the  character 
of  the  microstructure  vary  to  some  extent  with  the  size  of  the  dike,  and  to 
a  g-reater  extent  with  the  rate  at  which  the  mass  cooled,  for  each  of  the 
mineralogical  subdivisions  indicated  in  the  table,  still,  the  conditions  under 
which  these  various  magmas  cooled  having  been  quite  similar,  the  variations 
in  the  composition  and  microstructure  of  the  groundmasses  of  the  subdivi- 
sions named  bear  a  marked  relation  to  the  composition  of  the  rock  as  a 
whole  and  to  the  variations  in  the  phenocrysts.  This  will  appear  from  the 
following  descri2:)tions  of  the  rocks  belonging  to  the  subdivisions  in  Table  I: 

(a)  Groiiudniass  with  micropoikilitic  structure,  the  quartz  graius  iu  ono  case  being  0.09  mm.  to  0.43 
mm.  in  diameter,  and  containing  lath-shaped  microlites  of  feldspar,  gas  cavities,  and  microscopic 
hornblendes  and  biotites.  Abundant  phenocrysts  of  lime-soda  feldspar,  1  to  2  mm.  long,  and, 
smaller  ones  of  hornblende  and  biotite.  The  relative  proportions  of  the  latter  minerals  dift'er 
in  diti'erent  specimens.  As  the  total  amount  of  ferromagnesian  minerals  increases,  the  relative 
amount  of  hornblende  increases.  .Small  amounts  of  magnetite,  apatite,  and  zircon  occur  iu 
all  these  rocks. 

(h)  The  rocks  of  the  second  subdivision  are  nearly  the  same  as  those  of  the  first. 

(e)  In  the  third  division  the  micropoikilitic  structure  is  not  well  marked  and  grades  into  one  in 
which  lath-shaped  feldspar  microlites  are  more  prominent. 

(d)  and  (e)  Micropoikilitic  structure  is  wanting.  The  groundniass  is  composed  essentially  of  lath- 
shaped  microlites  and  grains  of  feldspar,  approaching  a  fel;  like  or  pilotaxitic  structure.  This 
change  accompanies  a  diminution  in  the  amount  of  (juartz.  In  these  five  subdivisions  pyroxene 
is  entirely  absent. 

(/)  and  ((/)  These  are  similar  to  the  last  two  subdi\'isions  in  microstructure  and  composition,  but 
pyroxene  was  originally  present  as  phenocrysts  and  has  been  nralitized.  Biotite  is  only 
present  in  shreds  in  the  groundmass  and  does  not  form  phenocrysts. 

(A)  is  represented  by  a  coarser-grained  rock,  but  slightly  porphyritic.  It  consists  of  lath-shaped 
feldspars  0.4  mm.  to  0.7  mm.  long,  between  which  is  a  very  small  amount  of  irregular  grains  of 
feldspar  and  quartz  and  ferromagnesian  silicates,  amphibole,  and  mica.  There  is  much 
uralitized  pyroxene,  which  formed  the  largest  idiomorphic  crystals. 

(i)  The  rock  of  this  division  is  like  the  last  in  microstructure,  but  is  more  porphyritic,  with  pheno- 
crysts of  plagioclase  and  pyroxene,  the  latter  iu  part  uralitized.  Near  the  contact  of  this  rock 
with  metamorphosed  sandstone  the  pyroxene  is  almost  colorless,  difl'erent  from  the  varieties 
common  in  the  pyroxene  rocks  of  this  region.  It  resembles  the  secondary  pyroxene  whicli  has 
resulted  from  the  alteration  of  hornblende  in  other  varieties  of  porphyry  in  this  neighborhood. 

The  more  quartzose  porphyries  and  the  coarse-grained  modifications 
cutting  the  stock  will  be  described  later.  The  microscopical  characters  of 
the  minerals  constituting  the  dike  rocks  are  nearly  the  same  throughout 
this  series  of  rocks. 


96      GEOLOGY  OF  THE  YELLOWSTON^E  NATIONAL  PARK. 

The  feldspar  in  all  cases  is  lime-soda  feldspai-,  with  the  usual  poly- 
synthetic  twinning.  In  sections  the  forms  of  the  feldspar  crystals  are  lath- 
shaped,  rectangular,  and  tabular,  the  general  habit  being  tabular  parallel  to 
the  clinopinacoid.  Zonal  structure  is  pronounced.  Their  range  appears 
to  be  from  labradorite  to  oligoclase,  the  former  prevailing  in  the  more  basic 
dike  rocks,  the  latter  in  the  more  siliceous  varieties  rich  in  biotite.  Primary 
inclusions  of  glass  or  of  other  minerals  are  scarce.  Secondary  inclusions 
are  more  numerous,  and  are  gas  cavities  or  needles  of  am]diibole.  The 
feldspars  are  more  distinctly  idiomorphic  than  the  hornblendes,  and  are 
sometimes  hvclosed  in  hornblendes.  More  rarely  hornblende  is  inclosed  in 
feldspar. 

Primary  hornblende  phenocrysts  are  generally  idiomorphic,  but  not 
always.  In  the  prism  zone  the  unit  prism  (110)  and  clinopinacoid  (010) 
are  well  developed.  Terminal  planes  are  seldom  observed.  Twinning  is 
common,  parallel  to  the  orthopinacoid  (100).  The  color  varies  from  brown 
to  green,  through  reddish  brown,  greenish  brown,  and  light  brown,  brownish 
gi-een,  and  olive  gray,  sometimes  with  a  reddish  tint  approaching  violet  gray. 
The  olive  gray  and  violet  gray  are  common  in  many  hornblendes  of  these 
dike  rocks.  The  pleochroism  is,  then,  ohve  gray  ||  C,  olive  brown  ||  Ij,  light 
brown  ||  a.  The  absorption  is  C>lJ>a:.  The  color  is  sometimes  in-egu- 
larly  distributed  in  the  crystal,  the  darker  shades  being  usually  in  the 
center,  but  zonal  structure  is  rare.  In  the  less  siliceous  rocks  of  this  series 
the  hornolendes  are  somewhat  darker  colored,  approaching  chestnut  brown. 
There  are  no  characteristic  inclusions.  When  associated  with  biotite  the 
two  minerals  are  so  intergrown  as  to  suggest  synchronous  crystallization. 
In  some  cases  biotite  is  inclosed  as  a  secondary  mineral.  The  hornblende 
is  in  various  stages  of  preservation,  sometimes  fresh,  sometimes  jiartially  or 
comjjletely  altered.  The  usual  alteration  products  are  chlorite  and  epidote, 
with  calcite  and  quartz.  Sometimes  compact  hornblende  has  been  changed 
to  fibrous,  "reedy"  amphibole. 

Biotite  forms  six-sided  plates,  occasionally  twinned  parallel  to  the 
cleavage  plane.  It  is  dark  reddish  brown  with  normal  absorption.  It  is 
sometimes  partially  bleached,  the  light-colored  spots  containing  bundles  of 
rutile  needles.  It  may  be  completely  altered  to  chlorite  and  epidote,  with 
calcite  and  quartz.  Pyroxene  was  not  found  in  an  unaltered  condition,  and 
was  only  identified  by  its  form.     The  iron  oxide  is  probably  magnetite,  with 


15 


U.   S.   GEOLOGICAL  SURVEV 


MONOGRAPH  XXXll       PA^IT  II       PL. 


SEPULCHRE    MOUNTAIN,    FROM    ITS   NORTHWEST   SPUR, 


16 


U  S  GEOLOGICAL  SURVEY. 


MONOGRAPH  XXXII,PARTII,PL  XVI, 


STOCK  HOCKS  AND  ArOPlIYSES.  97 

sonic  titanium.     Apatite  is  more  al)un(lant  In  the  more  micaceous  rocks. 
The  same  is  true  of  zircon 

Secondary  pyroxene  occurs  in  porphyries  within  the  metamorphosed 
sandstones,  apparently  derived  from  liornblende.  The  feldspar  and  biotite 
phenocrysts  are  quite  fresh,  and  the  general  microstructure  of  the  ground- 
mass  is  normal  for  a  hornblende-mica-andesite-porphyry.  The  augite 
substance  is  colorless  and  compact,  with  pyroxenic  cleavage.  It  occupies 
spaces  with  hornblende  outlines  in  cross  section,  the  plane  of  synnnetry  for 
both  minerals  being  the  same  No  pyroxene  outlines  were  observed.  Its 
refraction  and  double  refraction  are  high,  and  the  extinction  angle  is  large. 
It  sometimes  forms  irregular  grains  and  minute  aggregations  not  immediately 
connected  with  a  hornblende  crystal.  In  some  cases  the  hornblende  is  not 
entirely  changed  to  pyroxene.  The  process  by  which  this  alteration  took 
place  has  not  been  made  out. 

II    THE  STOCK  ROCKS  AND  APOPHYSES. 

The  diorite  forming  the  body  of  the  stock  varies  in  the  size  of  its 
crystals.  Most  of  it  is  medium  grained,  consisting  of  clusters  of  feldspars, 
and  others  of  ferromagnesian  minerals,  from  5  mm.  to  2  mm.  in  diameter, 
and  smaller.  The  coarsest  is  shown  in  fig.  1  of  PI.  XVII,  photographed 
natural  size.  The  size  of  the  component  crystals  is  smaller  than  that  of  the 
clusteiii,  and  is  from  1  mm.  to  2  mm.  A  medium-grained  form  is  shown  in 
fig  2  of  PI.  XVII.  The  grain  sinks  to  fine  grained  and  to  microcrystalline. 
The  variation  in  grain  is  gradual  in  some  parts  of  the  mass  and  rapid  in 
others.  The  finer-grained  portions  are  darker  colored.  While  a  gradual 
transition  from  coarse  to  fine  grained  and  from  light  to  dark-colored  rock 
can  be  traced  in  some  places,  the  two  extremes  are  in  juxtaposition  in 
others,  with  a  sharp  line  of  demarcation  between,  veins  of  the  light-colored 
rock  cutting  the  dark  colored.  In  places  also  there  are  fragments  of  various 
modifications  of  the  diorite  inclosed  in  diorite,  which  appears  to  be  a  later 
intrusion. 

The  dioi'ite  also  varies  in  mineral  composition.  For  the  most  part  the 
ferromagnesian  and  the  nonferromagnesian  minerals  are  in  about  equal 
proportions.  In  places  the  former  preponderate.  In  other  parts  of  the 
rock  the  other  minerals  are  in  excess.  The  minerals  recognized  megascop- 
ically  are  lime-soda  feldspar,  hornblende,  and  biotite.     In  places  biotite  is 

MON  XXXII,  PT  II 7 


98 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


abundant.  The  lighter- colored  varieties  of  the  rock  exhibit  quartz.  The 
finest-grained  porphyritic  forms  show  only  feldspar  and  pyroxene  pheno- 
crysts,  but  most  of  the  rock  is  evenly  granular,  with  no  porphyritic  structure. 
When  examined  microscopically,  the  constituents  are  found  to  be  hyper- 
sthene,  augite,  hornblende,  biotite,  lime-soda  feldspar,  orthoclase,  quartz.- 
These  are  not  all  in  every  modification  of  the  rock.  Their  range  of 
variation  is  indicated  in  Table  II,  in  which  a,  b,  etc.,  represent  different 
mineralogical  modifications  of  the  rocks. 


Table  IL — Mineral  variation  of  the  diorites  at  Electric  Peak. 


Pyroxene. 

Hornblende. 

Biotite. 

Labradorite. 

Oligoclase. 

Orthoclase 

Quartz. 

a  .. 
h... 
c... 
d  -. 

Little... 
Some  . . . 
Much  . . . 
Much  ... 
Much  . .. 
Much  ... 

Much... 

Much  .. . 
Some  . . . 
Some  ... 
Little . . . 

Some  . .. 

Little. 
Little. 
Some. 
Much. 
Much. 
Much . 
Much. 

Muih  ... 
Little . . . 

Much  ... 
Much... 
Much... 
Some  .. . 
Little... 

Some  . .. 

Some  . . . 
Some  . . . 
Much  . . . 
Much  .. . 
Much  .. . 

Little  . . . 
Little... 
Little . . . 
Little... 
Some  ... 

0 

f 

Much  . .. 

The  diorite  is  traversed  by  veins  or  dikes  of  equally  coarse-grained, 
lighter-colored  diorite,  sometimes  approaching  granite  in  composition.  In 
one  case  the  rock  is  fine-grained  granite  (fig.  1  of  PI.  XVIII).  In  .places 
there  are  narrow  seams  of  feldspar  and  quartz,  which  grade  into  rock 
containing  some  biotite  and  hornblende,  and  finally  into  quartzose  diorite. 
Such  seams  of  feldspar  and  quartz  appear  to  be  the  extremities  of  fissures 
or  cracks  in  the  early  solidified  magma,  into  which  the  fluid  portion  of  sub- 
sequently intruded  magma  has  been  forced.  They  are  of  truly  igneous 
origin,  and  consist  of  the  most  liquid  portion  of  the  magma,  or  that  part 
which  is  the  last  to  crj^stallize.  Segregations  rich  in  fen-omagnesian 
minerals  are  abundant  in  some  parts  of  the  rock. 

The  marginal  portions  of  the  diorite  core  are  diff"erent  in  difi'erent 
places.  In  some  there  are  porphyiy-like  modifications,  indicating  the  more 
rapid  cooling  of  the  margin  of  the  mass.  In  other  places  the  coarse-grained 
rock  is  directly  in  contact  with  the  wall  of  the  conduit,  showing  no  indica- 
tion of  chilling.  In  the  first  case  the  surrounding  rocks  must  have  been 
cooler  than  the  igneous  magma.     In  the  latter  case  they  must  have  been 


DIOKITES  OF  ELECTRIC  PEAK.  99 

equally  hot,  or  nearly  so,  iii(li('atiii<^  the  previous  heating' by  earlier  magmas. 
For  convenience  of  description  these  rocks  will  be  subdivided  into  the 
following'  grou])s : 

llrt.  Vtu'ieties  in  which  the  dark-colored  and  the  light-colored  minerals 
are  in  nearly  the  same  i)roportions. 

116.  Varieties  in  which  the  lig-ht-colored  minerals  are  in  excess  and 
the  amount  of  quartz  is  moderate. 

lie.  Like  116,  but  with  much  quartz. 

The  dai'k-colored  minerals  include  fen-omagnesian  minerals.  The 
others  are  feldspar  and  quartz. 

Ilrt.   VARIETIES    IN    WHICH    THE    DARK-COLORED    AND    LIGHT-COLORED     MINERALS 

ARE  NEARLY  EQUAL. 

This  group  includes  most  of  the  stock  rocks,  and  is  the  most  basic.  It 
embraces  a  series  of  varieties  that  grade  into  one  another  chemically, 
mineralogically,  and  structurally. 

As  regards  the  degree  of  •ciystallization,  or  the  size  of  the  grain  of  the 
rocks,  they  naay  be  classed  under  27  different  grades,  from  fine  to  coarse. 
But  no  attempt  has  been  made  to  establish  a  scale  of  uniform  degrees. 
The  arrangement  is  shown  in  Table  VIII,  Column  Ila.  At  the  coarsest- 
gi-ained  end  of  the  series  are  the  diorites  of  the  stock.  Their  structure  is 
hypidiomorphic  granular.  Some  of  the  mineral  constituents  have  their 
proper  crystallographic  outline,  but  most  of  them  are  irregularl)^  shaped. 

The  constituents  are  lime-soda  feldspars,  hornblende,  augite,  hyper- 
sthene,  biotite,  and  quartz,  with  magnetite.  The  feldspars  are  more  nearly 
idiomorphic  than  the  other  constituents.  They  are  rectangular  to  lath- 
shaped,  with  outlines  modified  by  the  juxtaposition  of  other  minerals. 
Quartz  forms  cementing  grains,  wholly  allotriomorphic.  Hornblende, 
pyroxene,  and  biotite  seldom  exhibit  crystal  boundaries,  and  penetrate  one 
another  intricately.  Magnetite  is  mostly  found  in  the  ferromagnesian  sili- 
cates.    Apatite  is  colorless  and  in  crudely  formed  crystals.     Zircon  is  rare. 

The  diorites  of  the  seven  highest  grades  of  crystallization,  Table  VIIT, 
Column  11a,  have  a  structure  similar  to  that  just  given,  but  vary  in  the 
relative  abundance  of  the  constituent  minerals,  as  shown  in  Table  V.  In 
the  coarsest  form  the  feldspars  are  from  2.5  mm.  to  1  mm.  long,  and  the 
quartz  grains  0.25  mm.  in  diameter.     The  structure  is  shown  in  PI.  XIX, 


100  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

fig  2.  In  the  seventh  grade  from  the  coarsest  end  the  feldspars  range  from 
1.25  mm.  to  0.5  mm.,  and  the  quartzes  are  about  0.12  mm. 

As  the  grain  becomes  smaller,  idiomorphic  forms  are  more  numerous, 
especially  of  hornblende  and  biotite.  And  these  are  more  idiomorphic 
when  quartz  is  more  abundant,  since  they  are  always  idiomorphic  with 
respect  to  this  mineral  (PI.  XIX,  fig.  3).  A  gradual  change  of  this  character 
can  be  followed  to  grade  26  of  the  table,  where  the  average  size  of  grain 
is  0.23  mm.  Here  there  is  a  slight  tendency  to  porphyritic  structure,  which 
does  not  show  megascopically.  Porphyritic  structure  becomes  noticeable 
in  grade  24  (PI.  XIX,  fig.  4),  and  still  more  so  in  grade  14.  This  has  a 
groundmass  composed  of  grains  of  feldspar  and  quartz  with  poorly  defined 
outlines,  besides  microscopic  pyroxenes  and  magnetites.  The  phenocrysts 
are  lime-soda  feldspar,  hypersthene,  augite,  and  some  irregular  patches  of 
biotite.  There  is  no  hornblende.  The  finest-grained  forms  of  these  rocks, 
grades  17  to  13,  have  similar  structures,  and  might  be  called  pyroxene- 
andesite- porphyry . 

This  group  of  rocks  presents  a  continuous  series  from  fine-grained 
andesite-porphyry,  with  phenocrysts  of  hypersthene  and  plagioclase,  to 
coarse-grained  honiblende-mica-diorite  with  a  variable  percentage  of 
pyroxene.  In  two  instances  the  transition  is  represented  by  specimens 
collected  within  short  distances  of  one  another.  Thus,  Nos,  268  to  271, 
279,  and  287  (PL  XIX,  fig.  3)  were  1  foot  apart  in  a  continuous  rock 
mass,  and  No.  266  is  from  the  same  mass.  Nos.  277,  278,  281,  284,  and  289 
are  from  one  rock  mass  exhibiting  a  gradual  change  of  grain  through  a 
distance  of  4  feet.     No.  267  is  from  the  same  mass. 

The  microscopical  characters  of  the  constituent  minerals  are  much  the 
same  throughout  the  series,  but  there  are  certain  featm-es  that  vary  with 
the  coarseness  of  grain  of  the  rock. 

The  feldspars  are  mostly  labradorite,  and  to  a  less  extent  andesiue. 
The  idiomorphic  crystals  and  the  zonal  portion  of  the  allotriomorphic  ones 
increase  in  size  as  the  grain  of  the  rock  becomes  larger.  Their  twin  lamellae 
become  broader,  the  number  of  inclusions  of  pyroxene  and  other  ferromag- 
nesiau  minerals  and  of  magnetite  diminish  with  increasing  grain,  and  the 
abundance  of  minute  dots  and  needle-like  inclusions  increases.  The 
feldspars,  forming  irregular  grains  in  the  groundmass  of  the  andesite- 
porphyries,  crystallize  as  a  border  around  the  idiomorphic  feldspai-s  in  the 


U.   S.   QEOlOOICAL  SURVEY 


MONOGRAPH    XXXII      PAHT   II      PL.    XVII 


H 


DIORITES. 
A.   Coarse  grain  ;   /?,    Medium  grain, 


U.   S.  GFOLCKICAL  SURVEY 


MONOGRAPH  XXXII      PART  II      Pl.XVIII 


.1,      GRANITE. 


li,      DIORITE-PORPHYRY 


DIOUITES  OF  ELECTUIC  PEAK.  101 

coarser-grained  varieties.  The  border  is  allotriomorphic  and  more  alkaline 
than  the  center.     Orthoclase  is  recognizable  in  the  coarsest-grained  rocks. 

Quartz  occurs  in  aHotriomorphic  crystals,  nearly  contemporaneous  with 
the  orthoclase,  which  is  also  allotriomorphic.  The  gas  and  fluid  inclusions 
in  the  quartz  increase  in  number  and  in  size  with  the  size  of  the  quartzes 
and  with  the  grain'of  the  rock. 

Hypersthene  and  augite  form  idiomorphic  and  allotriomorphic  indi- 
viduals in  the  porphyries.  They  are  much  more  irregularly  shaped  in  the 
coarsest-grained  rocks,  and  are  in  larger  individuals.  When  grown  together, 
the  hypersthene  is  always  the  older,  being  inclosed  by  the  augite;  rarely 
they  mutually  penetrate  one  another,  as  though  their  crystallization  was 
synchronous. 

Primary  brownish-green  hornblende  occurs  in  a  similar  manner.  It  fre- 
quently surrounds  the  pyroxenes  more  or  less  completely,  and  is  usually  the 
younger  growth.  Occasionally  it  appears  to  be  contemporaneous  with  augite. 
It  is  more  abundant  as  the  grain  of  the  rock  becomes  coarser.  Dark-brown 
hornblende  sometimes  is  present  as  an  independent  crystallization. 

Biotite  is  mostly  in  allotriomorphic  crystals.  The  ferromagnesian  min- 
erals occur  isolated  from  one  another  to  some  extent,  but  are  generally  inter- 
grown  in  the  most  intimate  manner.  Though  there  is  an  apparent  order  in 
the  time  of  their  crystallization,  beginning  with  hypersthene  and  augite  and 
ending  with  biotite,  still  in  most  cases  they  have  grown  synchronously. 
This  is  specially  true  in  the  coarser-grained  rocks. 

Magnetite  has  two  periods  of  crystallization  in  the  porphyritic  rocks,  but 
only  one  in  the  uniformly  granular  ones,  the  size  of  the  crystals  increasing 
and  their  number  dimini.shing.  Apatite  forms  abundant  minute  idiomorphic 
crystals  in  the  finer-grained  rocks,  and  fewer,  larger,  poorly  shaped  indi- 
viduals in  the  coarser-grained  rocks.  Zircon  is  more  noticeable  in  the 
coarser  rocks  and  is  in  larger  crystals. 

All  of  these  variations  of  character  plainly  indicate  that  the  physical 
conditions  that  brought  about  the  variation  in  the  texture  of  the  rocks 
affected  the  crystallization  of  the  earliest-forming  minerals,  and  since  these 
conditions  were  localized  in  the  stock,  it  follows  that  portions  of  the  igneous 
magma  were  completely  liquid  when  they  arrived  in  this  part  of  the  conduit. 

The  intergrowths  of  green  hornblende  with  pyroxene,  which  are  the 
results  of  primary  crystallization  in  these  diorites,  find  their  analogies  in 


102     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

similar  intergrowths  of  hornblende  and  pyroxene  in  unaltered,  often  pumi- 
ceous,  glassy  lavas.  They  are  to  be  distinguished  from  the  formation  of 
hornblende  from  pyroxene  by  secondary  processes  of  metamorphism, 
which  may  also  lead  to  the  production  of  compact  green  hornblende.  The 
transformation  of  both  pyroxene  and  compact  hornblende  into  fibrous 
amphibole  has  taken  place  in  some  of  these  rocks  to  a  limited  extent.  They 
are  in  general  very  fresh  and  unaltered. 

II&.  VARIETIES    IN    WHICH    THE    LIGHTCOLOEED   MINERALS    ARE    IN  EXCESS,    BUT 
IN   WHICH   QUARTZ   IS   NOT   EXCESSIVE. 

These  include  the  more  feldspathic  facies  of  the  diorite,  whether 
within  the  main  body,  on  its  margin,  or  as  dikes  or  veins  within  the  mass. 
There  is  considerable  quartz  and  a  range  of  ferromagnesian  minerals  that 
connect  them  with  the  preceding  varieties.  The  finer-grained  forms  approach 
the  dike  rocks  in  microscopical  characters,  and  are  possibly  connected  with 
them  geologically. 

Hornblende,  pyroxene,  and  biotite  are  similar  to  the  same  minerals  in 
the  main  body  of  diorite,  and  exhibit  the  same  relations  to  one  another 
when  in  juxtaposition,  but  vary  more  widely  in  their  relative  proportions, 
as  shown  in  Tables  V  and  VI.  The  feldspars  are  somewhat  more  alkaline, 
and  have  a  slightly  different  habit  from  those  in  the  main  diorite.  The 
quartz  plays  a  somewhat  difi"erent  role.  Its  crystals  occasionally  possess 
a  crudely  idiomorpliic  form,  and  because  of  their  greater  abundance  the 
microstructure  exhibits  more  of  a  granitic  appearance  than  in  the  less 
siliceous  diorites. 

The  coarsest-grained  variety  (313)  consists  of  broad  plagioclase  feld- 
spars from  1  mm.  to  2  mm.  long,  with  numerous  small  quartz  grains  located 
along  the  line  of  junction  of  the  feldspars;  hornblende  and  biotite  occur  in 
irregularly  shaped  anhedrons,  the  hornblende  being  in  part  phenocrystic. 
Magnetite  and  apatite  are  also  present.  When  the  grain  of  the  rock 
becomes  smaller  the  feldspars  stand  out  more  prominently  in  a  fine-grained 
groundmass.  The  porphyritic  texture  is  quite  pronounced  in  specimen 
308  from  near  contact  with  sedimentary  rocks.  Its  grade  of  crystalliza- 
tion is  27.  The  large  feldspars  and  hornblendes  are  idiomorphic.  The 
crystals  composing  the  groundmass  exhibit  an  approach  to  idiomorphism, 
especially  the  feldspars,  and  to  some  extent  the  quartzes.  This  structui'e  is 
shown  in  fig.  1,  PI.  XX. 


QUARTZ  MICA-DIOKITE.  103 

II  f.  VARIETIES  WITH  AN  EXCESS  OF  LIGHT-COLORED  MINERALS,  IN  WHICH  QUARTZ 

IS   AKUNDANT. 

These  include  very  quartzose  and  very  feldspatliic  varieties  of  diorite, 
approaching'  granite  in  conii)()sition  and  structure  (320  to  323,  275a  and 
286a).  Tliey  Jii"e  mostly  coarse-grained  dikes  or  veins  cutting  the  diorite 
mass.  They  correspond  to  grades  37  and  40,  Table  VIII.  In  this  group 
are  also  placed  certain  apophyses  (314-319)  from  the  stock  that  penetrate 
the  sedimentary  rocks. 

These  rocks  are  very  similar  to  those  of  Group  II&,  but  contain  more 
quartz,  and  the  feldspars  appear  to  be  still  more  alkaline.  Oligoclase- 
andesine  is  the  predominant  feldspar,  but  there  is  some  labradorite  and 
some  orthoclase.  Orthoclase  is  very  abundant  in  one  modification  of  the 
rock,  which  is  in  ftict  a  fine-grained  granite.  It  forms  a  large  body  on 
the  northeast  spur  of  Electric  Peak,  in  the  rugged  mass  of  dark-colored 
diorite  needles.  Its  crystallization  is  about  grade  35,  and  its  microstructure 
approaches  panidiomorphic,  as  shown  in  PI.  XX,  fig.  2.  The  other  varieties 
are  more  properly  quartz-mica-diorites.  In  the  coarsest-grained  forms  the 
ferromagnesian  minerals  are  biotite  and  hornblende,  with  no  pyroxene,  and 
with  biotite  in  excess  of  hornblende.  The  microstructure  of  one  of  the 
coarser-grained  varieties  (321),  grade  37,  is  shown  in  PI.  XX,  fig.  3,  and 
that  of  the  finest-grained  one  (314),  grade  19,  in  PI.  XXI,  fig.  1.  The 
latter  is  a  pronounced  porphyry. 

lie'.  Certain  narrow  apophyses  in  the  immediate  ^dcinity  of  the 
stock  are  rich  in  quartz,  but  contain  more  calcic  feldspar  and  a  variable 
amount  of  pyroxene,  besides  biotite  and  hornblende.  They  appear  to  be 
quartzose  facies  of  the  pyroxene-diorite  of  the  stock,  and  have  not  been 
found  cutting  the  main  body  or  forming  dikes  at  any  considerable  distance 
from  the  stock.  Their  mineralogical  composition  is  indicated  in  Table  Vll 
by  the  first  six  numbers  (314  to  319).  "With  increase  of  quartz  the  micro- 
structure  becomes  more  evenly  granular. 

III.  QUARTZ-MICA-DIORITE-PORPHYRY. 

The  last  magma  erupted  through  the  Electric  Peak  conduit  formed 
quartz-raica-diorite-porphyry.  It  is  a  broad  wedge-shaped  mass  cutting 
the  main  diorite,  narrower  toward  the  north,  and  sending-  out  dikes  into  the 
sedimentary  strata  to  the  southwest.     The  rock  is  light  gray  to  white,  with 


104  GEOLOGY  OF  THE  YELLOWSTONE  JfATIONAL  PARK. 

abundant  small  pheuociysts  of  feldspar,  quartz,  and  biotite.  Its  habit  is 
like  that  of  the  other  porphyries,  and  is  produced  by  the  great  number  of 
small  phenocrysts.  The  groundmass  is  hardly  recognized  megascopically, 
except  in  the  finest-grained  varieties.  The  coarsest  varieties  occur  within 
the  stock;  tlie  finest-grained  ones  in  the  narrow  dikes  cutting  the  southeast 
spur  of  Electric  Peak.  Their  grades  of  crystallization  are  shown  in  Table 
VIII,  Column  III. 

The  rock  is  intermediate  between  quartz-diorite-porphyry  and  granite- 
porphyry.  It  varies  slightly  in  mineral  composition  and  in  chemical  com- 
position, and  the  extremes  would  be  classed  under  these  two  kinds  of  rocks. 
Besides  biotite  there  is  a  little  hornblende  in  some  cases,  but  it  is  almost 
entirely  absent  from  most  of  the  rock.  The  biotite  is  partly  chloritized, 
and  the  feldspars  are  more  or  less  altered. 

In  the  finest-grained  varieties  the  groundmass  is  microcrj^stalline, 
approaching  microcrj'ptocrj'stalline.  The  phenocrysts  of  feldspar,  quartz, 
and  biotite  are  sharply  defined.  The  feldspar  is  mostly  oligoclase,  with 
possibly  a  little  orthoclase.  The  quartzes  are  smaller  than  the  feldsj)ars. 
Most  of  them  exhibit,  in  thin  sections,  straight-edged  crystallographic  out- 
lines. Others  are  rounded  more  or  less  completely.  Both  forms  occur 
together  in  the  same  rock  section.  In  some  cases  the  outlines  are  irregular 
because  of  bays  or  pockets  of  groundmass  let  into  their  sides.  These  occur 
in  otherwise  straight-edged  and  in  rounded  quartzes.  They  appear  to  be 
original  inclusions  rather  than  the  results  of  corrosive  action  of  the  magma 
on  idiomorphic  crj^stals.  There  are  bipyramidal  inclusions  of  glass  and 
others  of  gas  and  fluid.  In  coarser-grained  groundmasses  the  outlines  of 
feldspar  and  quartz  phenocrysts  are  not  so  sharply  defined,  but  are  jagged. 
Around  some  quartzes  there  is  a  narrow  border  of  groundmass,  part  of  which 
extinguishes  light  in  unison  with  the  quartz  phenocryst,  showing  that  the 
quartz  in  this  part  of  the  groundmass  has>  one  orientation  parallel  to  that  of 
the  quartz  phenocryst. 

The  con-esponding  rock  within  the  stock  is  much  coarser  grained,  with 
larger  and  more  numerous  phenocrysts,  so  crowded  together  as  to  leave  but 
little  groundmass.  The  feldspar  phenocrysts  are  similar  to  those  in  the  finer- 
grained  rocks,  but  those  of  quartz  gradually  lose  their  idiomorphic  shape  as 
the  groundmass  becomes  coarser,  and,  extending  out  among  the  smaller 
crystals  of  feldspar,  take  on  a  very  irregular  outline  (PI.  XX,  fig.  4).     There 


U.  S.  GEOLOGICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.   XIX 


r.-i )  <  36 


re;  X  28 


( D)x   29 


PHOTOMICROGRAPHS    OF   ANDESITE-PORPHYRY    AND    DIORITE 


THE  HELIOTYPE  PRINTING  CO.,  BOSTON 


U.  8.  QEOLOOICAL    SURVEY 


MONOQRAPH    XXXII     PART    II     PL.   XX 


I  Aj  ^    16 


rBjx    13 


fCj  %   22 


(J)j  <   20 


PHOTOMICROGRAPHS    OF   DIORITE    AND    DIORITE-PORPHYRY 


THE  HELIOTVPE  PRINTING  CO..  BOSTON 


U.  8.  OEOLOOICAL    SURVEV 


MONOGRAPH    XXXII     PART    II     PL.    XXI 


(B)  %   33 

PHOTOMICROGRAPHS    OF  DIORITE-PORPHYRY    AND    DACITE 


THE  HELIOTYPE  PRINTING  CO.,  BOSTON 


MINERAL  COMPOSITION  OF  DIKE  ROCKS.  105 

is  a  gradual  transition  from  the  sliarply  idiomorphic  quartz  plienocrysts  of 
the  fine-grained  poqihyries  to  allotriomorphic  crystals,  such  as  occur  in 
granites  and  in  the  coarser-grained  porphyries.  This  shows  that  the  por- 
phyritical  quartzes  were  the  last  ])lienocrysts  to  crystallize,  and  that  their 
crystallization  in  the  coarser-grained  varieties  continued  into  the  period 
of  crystallization  of  the  groundmass  without  evidence  of  interrujition. 

GENERAL    CONSIDERATION    OF   THE    MINERAL    AND    CHEMICAL    COMPOSITION 
OF    THE    INTRUSIVE    ROCKS    IN    ELECTRIC    PEAK. 

MINERAL    COMPOSITION. 

In  order  to  convey  an  idea  of  the  variations  in  mineral  composition  of 
the  rocks  just  described,  recourse  has  been  had  to  tabular  statements  of  the 
relative  abundance  of  the  constituent  minerals  in  the  different  grouj^s  of 
rocks.  The  tables  serve  not  only  to  condense  into  very  compact  space 
many  data,  but  place  them  in  such  form  that  they  may  be  comprehended  at 
a  glance,  while  at  the  same  time  the  formal  arrangement  of  the  data  often 
conveys  ideas  of  transitional  relationships  not  easily  expressed  otherwise. 
The  same  is  true  of  data  relative  to  degree  of  crystallization,  which  will  be 
explained  later  on. 

In  the  dike  rocks  constituting  GroujD  I,  and  in  the  dikes  of  Group  III, 
the  mineral  variations  most  readily  noted  affect  the  phenocrysts,  and  more 
particularly  those  of  the  ferromagnesian  minerals  and  quartz.  Variations 
in  the  feldspars  may  be  recognized,  but  with  more  difficulty,  and  may  be 
expressed  in  general  terms  by  saying  that  those  in  the  more  basic  rocks  are 
richer  in  calcium,  while  those  in  the  more  siliceous  rocks  are  richer  in 
sodium,  and  that  the  transition  between  the  extremes  appears  to  be  gradual. 
The  variations  in  the  phenocrysts  other  than  the  feldspars  are  indicated  in 
Table  III,  in  which  the  first  column  contains  symbols  of  mineralogical 
subdivisions  to  be  used  for  correlation  in  subsequent  tables.  In  this  table 
no  account  is  taken  of  the  degree  of  crystallization. 


106 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


Table 

III. — Mineral  variation  in  the  dike  rocks  of  Electric  Peak. 

Mineral 
groups. 

Specimen 
numbera. 

Phenocrj'stB  other  than  feldspar. 

Pyroxene. 

Hornblende. 

Biotite. 

Quartz. 

d, 

d, 

da 

d, 

d» 

de...:.. 

d, 

dn 

d9 

din 

dn 

f            232 
I            233 
234 
235 
f            236 
1            237 
f            238 
I            239 
240 
241 
242 
243 
244 
245 
246 
247 
248 
249 
250 
251 
252 
253 
254 
256 
257 
255 
258 
259 
260 
261 
262 
263 
264 
265 

Much 

Much 

Much 

Some 

Some 

Some 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Some 

Some 

Little 

Little 

Little 

Little 

Little 

Little 

Little 

Little 

Little 

Little    . 

Little 

Little 

Little 

Little 

Little 

Some 

Some 

Some     

Much 

Much 

Much    ... 

Much    

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Little 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

The  transition  indicated  in  the  table  is  from  acidic  rocks  with  much 
porphyritical  quartz  and  biotite  and  very  Httle  hornblende,  through  inter- 
mediate rocks  with  much  porphyritical  biotite  and  hornblende,  to  basic 
rocks  with  pyroxene  and  little  or  no  porphyritical  hornblende  or  biotite, 
but  which,  being  more  coarsely  crystalline,  contain  some  biotite  as  a  product 
of  the  final  consolidation  of  the  groundmass,  which  is  related  in  its  occrn'rence 


CRYSTALLIZATION  OF  DIKE  EOGKS. 


107 


to  the  biotite  in  the  diorite.     The  gradual  nature  of  the  transition  from  one 
extreme  to  the  otlier  is  apparent  at  a  ghxnce. 

The  impossihiUty  of  considering  certain  rocks  as  definite  types  with 
which  to  compare  other  rocks  in  the  region  is  also  evident  when  it  is 
observed  that  tlie  mineralogical  variation  takes  place  within  certain  limits 
in  one  rock  body  (Nos.  247,  250,  255,  256,  and  257  are  from  the  same 
dike),  and  that  what  appears  to  be  a  mineralogical  modification  of  one 
particular  rock  body  is  the  characteristic  combination  of  another,  and  its 
modification  is  something  different.  Field  observation  shows  that  in  this 
locality  the  greater  number  of  dikes  are  composed  of  rocks  with  variable 
percentages  of  porphyritical  hornblende  and  biotite,  and  that  the  other 
varieties  are  less  numerous.  In  another  region  other  varieties  ^predominate. 
The  chemical  variations  which  are  indicated  by  the  silica  percentages 
range  from  57.12  in  subdivision  ds  to  61.85  in  (!■„  and  probably  reach  69.00 
in  rfij.  They  indicate  a  correspondence  between  the  mineralogical  and 
chemical  variations  for  this  group  of  rocks. 

Table  IV. — Grades  of  crystallization  of  the  dike  rocks  of  Electric  Peak, 


Grades 
of  crystal- 
lization. 

Mineralogical  grouping  indicated  in  Table  HI. 

d, 

d. 

da 

di 

d. 

d. 

d. 

ds 

d. 

dio 

d.i 

6 

259 

260,  261 
262,  263 
264,  265 

7.. 

240 

8 

238 

9. 

•  ■ 

241,242 

243 

244, 245 

258 

10 

246 

11 

25.5,  256 
257 

12  

239 

249,  250 
251 

252, 253 
254 

13 

14 

247,  248 

16 



235 

19 

20 

25 

232 
233 

236,237 

234 

Table  IV  expresses  the  range  in  degree  of  crystallization  of  the  ground- 
mass  of  these  rocks,  which  are  arranged  in  columns  corresponding  to  the 
mineralogical  grouping  of  Table  III.  It  is  to  be  remarked  that  the  speci- 
mens were  collected  from  different-sized  dikes  and  from  different  parts  of 
the  dikes,  so  that  the  variations  in  grain  can  not  be  compared  very  closely 


108  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

with  the  mineral  composition.  But  when  the  size  of  the  dikes  in  each  case 
is  taken  into  consideration  it  becomes  even  more  evident  than  from  the 
table  that  the  coarseness  of  grain  bears  a  very  considerable  relation  to  the 
chemical  composition  of  the  rock.  The  variation  in  grain  between  the  sides 
and  center  of  a  dike  and  between  dikes  of  different  widths,  for  rocks  of 
nearly  the  same  composition,  is  not  so  great  as  the  variation  between  rocks 
of  different  composition  where  the  size  of  the  dikes  in  which  they  occur  is 
somewhat  similar.  Thus,  specimen  No.  233  is  from  the  center  of  a  4-foot 
dike,  and  No.  232  from  the  contact  wall  of  the  same;  and  specimen  No.  247 
is  from  the  center  of  an  8-foot  dike,  and  Nos.  257  and  250  are  from  the 
contact  walls  of  the  same;  Nos.  264  and  265  are  from  4-foot  dikes,  and 
No.  263  is  from  a  2-foot  dike.  They  all  occur  at  nearly  the  same  altitude, 
but  it  is  possible  that  the  pyroxene-bearing  rock,  No.  233,  may  have  been 
intruded  in  rocks  which  were  more  heated  at  the  time  of  its  intrusion  and 
so  have  acquired  its  degree  of  crystallization  through  slower  cooling,  but 
this  is  not  so  likely  to  have  happened  in  the  case  of  rock  No.  234,  which 
is  in  the  same  part  of  the  mountain  as  No.  235,  but  is  in  a  dike  10  feet 
wide  and  is  very  much  coarser  grained  than  No.  233.     (See  Table  VIII.) 

The  groundmass  of  the  rock  with  porphyritical  quartz  and  biotite,  No. 
265,  is  made  iip  of  minute  grains  of  quartz  and  feldspar,  about  0.015  mm.  ua 
diameter,  while  the  groundmass  of  the  pyroxene-bearing  variety.  No.  233,  is 
made  up  of  lath-shaped  and  irregularly  shaped  feldspar  about  0.10  mm.  to 
0.14  mm.  in  length,  and  the  groundmass  of  No.  234  is  composed  of  lath- 
shaped  feldspars  0.5  mm.  to  0.7  mm.  in  length. 

The  character  of  the  gi-oundmass  changes  from  an  even  granular 
structure  in  the  acidic  rocks,  through  one  made  up  of  irregular  grains  and 
latli-shaped  feldspars  in  the  intermediate  rocks,  to  an  aggregation  of  lath- 
shaped  feldspars  with  almost  no  irregular  grains  in  the  basic  varieties. 

The  tendency  of  basic  rocks  to  crystallize  more  completely  and  with 
larger  groundmass  crystals  than  acidic  rocks  is  constantly  observed  among 
the  extrusive  rocks,  such  as  basalts,  andesites,  and  rhyolites.  The  same 
law  appears  to  obtain  among  the  intrusive  rocks.  It  is  of  course  necessary 
to  compare  rocks  that  appear  to  have  crystallized  under  very  nearly  the 
same  physical  conditions. 

The  rocks  of  Group  II  have  been  described  in  greater  detail  on  account 
of  their  number  and  importance,  and  have  been  subdivided  into  three  sub- 


MINERAL  COMPOSITION  OF  DIOKITES. 


109 


grou]is,  Ilrt,  II/>,  He.  The  tables  presenting  the  results  of  this  part  of  the 
work  have  a  ditierent  form  and  are  arranged  separately  for  each  subdivision. 
They  are  Tables  V,  VI,  and  VII. 

Table  V. — Mincralogical  variation  among  the  diorites  of  Group  Ila. 


1 

1 
1 

o 

«■ 
ga  ^ 

Amount  uf  <|ujirtz. 

Kclative    iiiiioiint   of   pyroxene  and 
hornblende. 

Uelative  amount  of  pyrox- 
ene, hornblende,  and  bio- 
tite. 

Little. 

Mod- 
erate. 

Con- 
sider- 
able. 

Much. 

p. 

P>h. 

p=h. 

p<h. 

h. 

(ph).  (ph)>b. 

{ph)=b. 

(ph)<b. 

266 

267 
268 
269 
270 
271 
272 
273 
274 
275 
276 
277 
278 
279 
280 
281 
282 
283 
284 
285 
286 
287 
288 
289 
290 
291 
294 
295 
296 
297 
298 
299 
300 

57.38 

266 

266 
267 
268 
2 
270 

266 

267 

268 
269 
270 
271 

r2 

267 
268 
269 
270 
2 

39 

271 

71 

61.22 
58.05 
56.33 

2 
273 
274 

272 

272 
273 



273 

274 

274 

275 

275 
276 
277 

278 

275 
276 
77 

58.10 

276 

2 

?7 

2 

278 

278 
279 

279 

279 
280 
281 



280 
2 



280 
31 

282 
33 

58.11 

58.87 

51 

2 

282 
2 

282 

B3 

2: 

« 

2 

2 

!4 

284 

284 

55.64 

285 
286 

285 

285 
36 

287 
288 
39 

286 
2S 

2 

287 
288 
2 
290 
291 

n 

288 
2S 

S9 

•---.. 

id 

2 

*290 

il 

290 

n 

2S 
294 

296 

2 
294 
2 

56.28 

53.72 
55.  23 

294 

296 
297 
298 

2 

15 

■ 

2 

95 

' 

296 

*297 

297 

298 

298 
(9 

299 
3 

299 
)0 

2 

)0 

3 

300 

*  The  hornblende  in  these  rocks  is  in  part  secondary ;  pyroxene  may  have  heen  present  originally. 


110  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  VI. — Mineralogical  variation  among  the  diorites  of  Group  lib. 


1 

B 

d 

g 

a 

03 

o 

be 

a  ca 

o 
® 

PM 

AraouDt  of  quartz. 

Relative   amouut  of   pyroxene    and 
hornblende. 

Kelative  amonnt  of  pyrox- 
ene, hurnblende,  and  bio- 
tite. 

Little. 

Mod- 
erate. 

Con- 

sid  er- 
able. 

Much. 

P- 

P>h. 

p=h. 

p<h. 

h. 

(ph). 

(2>ft)>6.  {ph)=b. 

(phXb. 

301 
302 
303 
304 
305 
306 
307 
308 
309 
310 
311 
312 
313 

301 
302 
303 

301 

302 
}3 
304 
305 
306 
307 
308 



301 

3 

yi 

65.60 

3 

303 

304 

304 

65.94 

305 
306 
307 
308 

}9 
310 
311 

12 
313 

305 

306 

63.78 

307 
3 

)8 
309 
310 
311 

12 





64.07 

3 

*309 

t310 

65.11 

311 
312 

3 

3 

64.85 

313 

313 

] 

*  This  rock  belongs  'witb  288,  resembles  it  in  structure  and  character,  but  is  higher  in  silica  and  feldspar, 
t  An  exceptional  variety,  from  talus. 


Table  VII. — Mineralogical  variation  among  the  diorites  of  Group  lie. 


1 

s 

9 

a 
1 
1 

Cm 

O 

Xit, 

O   CD 

O 

Amount  of  quartz. 

Relative  amount    of   pyroxene    and 
hornblende'. 

Relative  amount  of  pyrox- 
ene, hornblende,  and  bio- 

tite. 

Little. 

Mod- 
erate. 

Con- 
sider- 
able. 

Much. 

P- 

P>h. 

p=h. 

P<h. 

h. 

Iph). 

(ph)>b. 

(ph=b.) 

lph)<b. 

314 

315 

316 

317 

318 

319 

320 

321 

286o 

27oo 

322 

323 

- 

314 

315 

316 

317 

318 

319 

320 

321 

286u 

275a 

322 

323 

315 
316 

14 

3 

4 

315 
,316 

318 
319 
320 
321 
286fl 
275a 
322 
23 

.-_-.. 

65.48 
65.80 

3 

318 

7 

317 

319 

320 
321 
Sa 
275o 
322 
323 

67.54 

28 

66.05 

3. 

*  The  first  six  rocks  in  this  group  are  closely  related  to  the  main  mass  of  the  diorite  of  G-roup  Ila. 


MINERAL  COMPOSITION  OF  DIOItlTES.  Ill 

Table  V  j)reseiits  those  varieties  of  the  stock' rocks  in  which  the  amount 
of  the  ferromaf^uesiau  siHcates  about  equals  that  of  the  feldspar  and  quartz 
combined.  There  is  no  distinction  made  as  to  whether  the  crystals  occur 
as  phenocrysts  or  not.  They  are  arranged  in  a  series  according  to  their 
degree  of  crystallization,  the  finest  grained  being  at  the  top,  the  value  of 
the  degrees  of  crystallization  liaving  been  already  explained  (p.  99).  The 
silica  percentage  is  given  in  all  cases  where  it  has  been  determined.  In  the 
table  an  attempt  is  made  to  express  the  relative  amounts  of  the  quartz,  of 
the  hornblende  and  pyroxene,  and  of  the  biotite  and  hornblende  and 
pyroxene.  The  i-elative  amount  of  feldspar  is  not  expressed.  In  a  general 
way  it  varies  inversely  as  the  amount  of  quartz  for  this  subgroup.  The 
columns  under  the  different  divisions  of  the  table  express  certain  relations 
of  the  minerals  approximately.  Under  the  divisions  of  quartz,  the  terms 
"little,"  "moderate,"  "considerable,"  "much"  are  used  only  as  comparative 
terms  applicable  to  this  group  of  rocks  throughout  its  three  subdivisions, 
Ilrt,  lib,  lie,  and  have  no  reference  to  the  relative  amount  of  quartz  which 
might  be  found  in  another  suite  of  rocks.  Consequently,  what  would  be 
considered  "much"  quartz  in  these  rocks  might  be  only  a  moderate  amount 
for  another  series. 

Under  the  division  which  shows  the  relative  amounts  of  pyroxene  and 
hornblende  in  each  rock,  the  first  column,  "^,"  indicates  that  there  is 
pyroxene  and  no  hornblende;  the  next  column,  that  the  pyroxene  is  in 
excess  of  the  hornblende;  the  third,  that  they  are  equal;  and  so  on.  The 
relative  amounts  of  pyroxene  or  of  hornblende  in  any  two  varieties  of  the 
rock  is  not  indicated  directly.  It  can  be  ascertained  roughly  by  consider- 
ing that  in  this  subgroup  the  sum  of  the  pyroxene,  hornblende,  and  biotite 
is  nearly  constant. 

In  the  next  division  of  the  table  the  amount  of  the  biotite  is  compared 
with  that  of  the  pyroxene  and  hornblende  combined,  in  the  manner  already 
explained  for  the  previous  division. 

The  first  fact  brought  out  by  a  study  of  this  table  is  the  variability  of 
the  quartz  percentage,  which  does  not  appear  to  hold  a  very  definite  relation 
to  the  silica  percentage,  as  in  the  case  of  Nos.  281  and  282.  But  it  is 
observed  in  studying  the  thin  sections  that  the  quartz  is  not  so  noticeable  in 
the  fine-grained  varieties  as  in  the  coarse-grained  ones,  and  may  therefore 
be  either  overlooked  or  possibly  not  so  strongly  developed.     Thus  the 


112     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

coarse-grained  varieties  with  little  quartz  are  lower  in  silica  than  the  fine- 
grained varieties  with  little  quartz.  (Compare  Nos.  297  and  298  with  Nos. 
272,  273,  and  274.)  It  is,  of  course,  evident  that  in  rocks  with  variable  per- 
centages of  the  essential  minerals  which  are  all  silicates  there  can  be  no 
rigid  relation  between  the  proportion  of  any  one  of  these  minerals  and  the 
silica  percentage  of  the  rock  within  the  narrow  range  of  chemical  variation 
that  occurs  in  this  group.  In  it  the  silica  does  not  vary  7  per  cent,  and  the 
amounts  of  the  other  chemical  constituents  are  the  modifying  chemical 
factors.  This  will  be  discussed  more  fully  when  the  chemical  composition 
of  the  rocks  is  considered. 

The  most  regular  variation  is  in  the  relative  proportions  of  pyroxene 
and  hornblende.  There  is  a  definite  increase  in  the  amount  of  hornblende 
and  decrease  in  that  of  pyroxene  as  the  rock  becomes  coarser  grained. 
This  is  specially  noticeable  in  those  specimens  forming  series  from  one  spot, 
Nos.  268,  269,  270,  271,  279,  and  287,  and  Nos.  277,  278,  281,  284,  and  289. 
The  variation  in  the  relative  amount  of  biotite  is  not  so  marked,  but  there 
is  a  slight  increase  from  the  fine-grained  to  the  coarse-grained  end  of  the 
series. 

The  irregularities  in  the  variations  of  the  diff'erent  minerals  could  be 
better  understood  if  the  chemical  composition  of  all  of  the  diff'erent  varieties 
of  the  rocks  were  known,  but  such  an  investigation  is  not  practicable.  The 
rocks  of  this  subgroup  may  be  classed  among  the  pyroxene-diorites  and 
quartz-pyroxene-diorites.  They  carry  considerable  biotite,  and  pass  into 
quartz-mica-diorite  at  one  end  of  the  series  and  into  pyroxene-porphyrite  at 
the  other. 

Tables  VI  and  VII  include  those  varieties  of  rock  in  which  the  amount 
of  feldspar  and  quartz  together  exceeds  that  of  the  ferromagnesian  silicates, 
Table  VII  including  those  varieties  particularly  rich  in  quartz. 

The  silica;^ percentage  is  considerably  higher  in  these  rocks  than  in  those 
of  the  previous  subgroup.  The  quartz  is  more  uniform,  and  on  the  whole 
is  higher.  It  is  very  considerably  higher  in  Subgroup  lie.  Pyroxene  is 
absent  from  most  of  the  varieties,  but  occurs  in  small  amounts  without 
hornblende  in  a  few  instances  already  noticed.  Biotite  is  more  variable  in 
Subgroup  lib  than  in  lie,  where  it  is  the  predominant  ferromagnesian  silicate. 
The  relation  of  quartz,  biotite,  hornblende,  and  pyroxene  to  the  chemical 
composition  of  the  different  varieties  of  this  series  of  rocks  is  not  so  definite 


CRYSTALLIZATION  OF  DIKE  AND  STOCK  ROCKS. 


113 


as  ill  the  case  of  the  group  of  dike  rocks.  In  general,  quartz  and  biotite 
are  more  aliundaiit  in  tlie  more  acid  varieties  of  the  coarse-grained  rocks, 
but  they  both  appear  in  the  V)asic  varieties  when  they  are  coarsely  crystal- 
line. Tile  relations  of  hornblende  and  pyroxene  to  the  chemical  composi- 
tion of  rocks  are  not  elucidated  in  any  way  by  the  study  of  this  group  of 
rocks.  It  is  evident,  however,  that  in  the  intrusive  rocks  of  this  region 
hornblende  is  developed  to  a  greater  extent  in  the  basic  rocks,  in  propor- 
tion as  they  are  coarser  grained,  and  that  j)yroxene  is  more  abundant  in  the 
finer-grained  forms  than  in  the  coarser. 

The  mineral  com})osition  of  the  quartz-mica-diorite-porphyry,  Group 
III,  is  very  uniform,  and  needs  no  tabulation.  It  contains  very  much 
quartz,  abundant  biotite,  and  almost  no  hornblende ;  the  greater  part  of  the 
rock  is  more  siliceous  than  the  main  body  of  the  diorite,  and  reaches  69.24 
per  cent  of  silica,  but  a  facies  of  it  which  is  richer  in  hornblende  than  the 
body  of  the  rock  has  only  65.97  per  cent  of  silica. 

Table  VIII. — Grades  of  crystallization  of  the  dike  and  stock  rocks  of  Electric  Peak.. 


Grade. 

I. 

II  (o). 

II  (6). 

II  (c). 

HI. 

d,  to  dm. 

«i. 

«.,. 

«3- 

«4  ftnd  d||. 

6 

' 

259 
260,  261 
262,  263 

264,  265 

7 

240 

238 

f     239 

I  241,  242 

243,  246 

(    244,  245 

1  254,  256 

f  239,249 

I  250,  257 

251 

f  247,248 

1  252,253 

8 

y 

1 : 

10 

f 

11 

12 

13 

266 

1     267 

268 
269 
270 

14 

15 

16 

235,  254 

17 

301 
302,  303 

304 

305,  306 
307 

18 

le 

(            232 

1  236,237 

233 



1 

314,  315 

20 

324,  325 
326,  327 

21 



.1 

MON   XXXII,  PT   II 8 


114 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


Table  VIII. —  Grades  of  crystallization  of  the  dil'e  and  stoelc  rocks  of  Electric 

Peak — Coutiuued. 


Grade. 
22 

I. 

II  (a). 

II  (!)). 

II  (C). 

III. 

d|  t(»  rfio. 

»,. 

»j. 

Ss- 

»4  and  d||. 

271 

328,  329 

330,  331 

332 

333 

23 

272 
273,  274 

24 

316 
317 

25 

234 

'>6 

275,  276 

97 

277 

308 

98 

278 

279 

280,  281 

282,  283 

284 

|-     285 

I  286,287 

288 

289 

99 

30 

31 

^9 

33       

1 

SA 

309 
310 
311 

35  

{ 

318 
319 
320 
321,  286a 

334 

36 

37 

290 

291 
294 

295 

296 
297 
298 
299 
300 

38 

312 
313 

39 

40 

{ 

275« 
322,  323 

41 

49 

1 

43 



45 

Table  VIII  expresses  the  relative  degree  of  crystallization  of  all  the 
intrusive  rocks  collected  from  the  stock  and  dikes  of  Electric  Peak.  They 
are  an-anged  in  the  groups  already  described.  The  breaks  in  the  different 
columns  do  not  signify  breaks  in  the  gradation  of  crystallization  in  the  rock 
bodies  in  the  field,  but  simply  that  the  specimens  collected  are  not  from  all 
the  different  structural  phases  of  the  different  rocks.  However,  the  clus- 
tering of  the  numbers  in  particular  parts  of  the  scale  indicates  the  prevailing 
grain  of  the  rocks  as  they  are  exposed  at  the  present  time. 


CHEMICAL  COMPOSITION  OF  ELIX'TUIC  PEAK  KOCKS.  1 15 

It  is  not  possible  to  draw  a  liiu'  of  (U'luarcatiiiu  anywlieiv  iu  the  scale 
based  on  the  dej^ree  of  crystallization  between  rocks  that  occur  in  narrow 
dikes  and  those  that  form  parts  of  much  larger  bodies.  A  relation  between 
the  degree  of  crystallization  and  the  size  of  the  rock  bod}'  does  not  at  first 
appear  when  all  of  these  occurrences  are  considered  together.  The  very 
important  influence  of  several  other  factors,  however,  becomes  apparent. 
One  is  the  chemical  character  of  the  magma,  the  more  basic  magmas  tend- 
ing to  crystallize  coarser  than  the  more  siliceous  ones  under  similar  physical 
conditions.  Another  factor  is  the  previous  temperature  of  the  rocks  into 
which  the  molten  magmas  were  injected,  and  the  consequent  differences  in 
the  rate  of  cooling  which  the  molten  magmas  experience.  There  niay  also 
be  other  factors  which  influence  the  crystallization  in  certain  cases,  but 
they  are  not  evident  in  the  occuiTences  at  Electric  Peak.  In  this  locality 
the  chief  factor  influencing  the  crystallization  appears  to  have  been  the 
temperature  of  the  inclosing  rocks  at  the  time  of  the  diff"erent  intrusions. 
The  next  most  influential  factor  appears  to  have  been  the  chemical  character 
of  the  magma  itself,  and  the  third  the  size  of  the  intruded  mass.  In  another 
region  the  relative  importance  of  these  factors  may  be  different. 

CHEMICAL   COMPOSITION. 

The  chemical  composition  of  the  intrusive  rocks  at  Electric  Peak  is 
shown  by  the  analyses  in  Table  IX.  Nos.  272  and  3(i9  were  made  by  Mr. 
W.  H.  Melville,  the  remainder  by  Mr.  J.  E.  Whitfield.  All  are  from  rocks 
occurring  in  the  stock  and  its  immediate  apophyses.  They  represent  the 
composition  of  various  forms  of  the  diorite  and  diorite-porphyry.  The 
first  four  analyses,  Nos.  295,  267,  273,  and  272,  are  from  the  main  body  of 
the  stock,  and  belong  to  Subgroup  Ila.  The  next  four  analyses,  Nos.  309, 
313,  311,  and  303,  are  from  modifications  of  the  main  body  of  the  diorite 
and  from  one  of  the  lighter-colored  veins  or  dikes  which  traverse  it.  They 
belong  to  Subgroup  Ilh.  Two  more  varieties  of  the  main  stock  are  repre- 
sented by  analyses  Nos.  323  and  321.  They  are  quite  siHceous,  and  belong 
to  Subgroup  lie.  Analyses  Nos.  329  and  326  are  from  the  large  body  of 
quartz-mica-diorite-porphyry,  the  first  being  a  basic  variety  of  it,  and  the 
second  corresponding  more  nearly  to  the  general  character  of  the  body  of 
the  rock. 


116  OEOLOGY  OF  THE   YELLOWSTONE  NATIONAL  PARK. 

Table  IX. — Chemical  analyses  of  intrusive  rocks  from  Electric  Peak. 


Constituent. 

295 

267 

273 

272 

309 

61.07 

313 

311 

303 

65.60 

329 

323 

321 

326 

SiO;    .... 

56.  28 

57.38 

58.05 

61.22 

64.85 

65.11 

65.97 

66.05 

67.54 

69.24 

TiO,  .... 

.84 

Trace. 

1.05 

.61 

.45 

.91 

.71 

.  75 

.42 

.34 

.80 

.65 

Al,03  ... 

14.23 

16.86 

18.00 

16.14 

15.82 

16.57 

16.21 

17.61 

16.53 

16.96 

17.02 

15.30 

FegOs  ... 

4.69 

2.49 

2.49 

3.01 

3.40 

2.10 

1.06 

.95 

2.59 

2.59 

2.97 

L72 

FeO  .... 

4.05 

5.17 

4.56 

2.58 

1.44 

2.15 

3.19 

2.76 

L72 

1.38 

.34 

.69 

NiO 

.09 
Trace. 

.05 
Trace. 

MnO.... 

.16 

Trace. 

None. 

None. 

None. 

None. 

None. 

None. 

Trace. 

Trace. 

CaO  .... 

7.94 

7.32 

6.17 

5.46 

4.43 

4.01 

3.97 

3.72 

3.37 

3.37 

2.94 

2.98 

MgO.... 

6.37 

5.51 

3.55 

4.21 

3.39 

2.14 

2.57 

1.  49  !     2. 11 

2.08 

L51 

.95 

LiiO 

.01 

.39 

None. 

None. 

.04 

.03        .09 

None. 

.03 

None. 

Na,0.... 

2.98 

3.33 

3.64 

4.48 

4.06 

3.71 

4.00 

4.36       3.41 

4.20 

4.62 

4.46 

K:0 

1.23 

L45 

2.18 

1.87 

2.27 

3.10 

2.51 

2.36  1    2.67 

2.53 

2.28 

2.52 

P,Os  .... 

.40 

Trace. 

.17 

.25 

.18 

.14 

.02 

.16  Trace. 

Trace. 

Trace. 

Trace. 

SO, 

Trace. 

.21 

.07 

Trace. 

Trace. 

Trace.         .  13 

.03 

.26 

.27 

CI 

H:0   .... 
Total. 

.17 
.93 

.17 
.42 

Trace. 

.86 

None. 
.35 

None. 
.94 

None.  1      .  09  Trace. 

.15 
.55 

Trace. 
1.30 

.44 

.52 

.59 

1. 23         .  69 

100.  28 

100.  70 

100.  79 

100.36 

100. 08 

100. 03 

100. 33 

100.38  '100.33  '100.22 

101.01   100.08 

Less  0 

1 

for  CI . 

.04 

.04 

j      .02 

.03 

100. 24 

100.66 

100. 31 

100.98 

Table  X. — Silica  percentages  of  rocks  from  Electric  Peak. 


Sheet 
rocks. 

Dike  and  stock  rocks. 

SiO^. 

I. 

Ila.       i        116. 

lie. 

III. 

53.72 
55.23 
55.64 
56.28 
56.33 

53.72 
55.23 
55.64 
56.28 
56.33 
57.12 
57.  38 
58.05 
58.10 
58.11 
58.49 
58.87 
59.64 
60.54 

57. 12 

57.38 
58.05 
58.10 
58.11 

58.49 

58.87 

59.64 

60.54 

SILICA  PERCENTAGES  OF  ELEOTKIO  PEAK  ROCKS. 
Table  X. — Silica  percentages  of  rocks  from  Electric  Peak — Continued. 


117 


Sheet 
rocks. 

Dike  null  8tuck  rocka. 

SiO,. 

60.36 
60.89 
61.50 
61.85 
63.01 
63.78 
64.85 
65.11 
65.48 
65.60 
65.80 
65.94 
65.97 
66. 05 
67.54 
69.24 

I. 

IIo.                116. 

He. 

in. 

60.56 

60.89 



61.50 

61.85 

63.01 
63.78 
64.85 
65.11 



65.48 

65.60 

65.80 

65.94 

65. 97 

66.05 
67. 54 



69.24 

•  Fio.  1. — Variatiou  oT  silira  perceutayes  of  rocks  Irom  Electric  Peali. 

Tlie  silica  percentages  of  a  number  of  varieties  of  these  rocks  were 
determined  and  are  given  in  Table  X,  together  with  those  from  the  complete 
analyses.  In  a  measure  they  supplement  these  analyses  and  demonstrate 
what  is  evident  from  the. microscopical  study  of  the  thin  sections,  namely, 
that  the  diorites  and  porphyries  pass  through  all  possible  gradations  from 
one  extreme  to  the  other.  The  character  of  this  transition  is  shown  by  the 
diagram,  fig.  1,  in  which  each  determination  is  given  the  same  weight.  The 
series  is  arranged  according  to  the  increase  of  silica,  and  the  silica  percent- 
ages are  plotted  as  ordinates. 


118  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Ill  Table  X  the  percentages  are  all  placed  in  the  extreme  right-hand 
column,  and  also  in  separate  columns  corresponding  to  the  groups  described 
in  the  first  part  of  the  paper.  From  this  it  is  seen  that  the  main  body  of 
the  diorite  varies  from  53.72  to  60.56  per  cent  of  silica,  and  in  certain  con- 
tact forms  reaches  67.54  per  cent.  The  dikes  of  later  rocks  related  to  the 
diorite  and  cutting  the  main  body  of  the  stock  range  from  63.78  to  69.24 
2)er  cent. 

Of  the  various  bodies  of  magma  that  have  followed  one  another 
through  the  conduit  at  Electric  Peak,  there  is  a  variation  in  chemical  com- 
position in  each,  the  different  series  of  changes  overlapping  one  another. 
Thus  the  average  chemical  composition  of  each  subgroup  of  varieties  shifts 
somewhat,  and  is  more  basic  for  one  than  for  another.  But  the  end  varieties 
of  each  subgroup  overlap,  so  that  tlie  most  basic  modification  of  the  more 
acid  group  is  more  basic  than  the  most  acid  end  of  the  more  basic  group 
which  immediately  preceded  it. 

Since  the  rocks  of  Grroup  I  belong  to  outlying  dikes  of  the  main  stock 
and  are  contemporaneous  with  it,  their  silica  percentages  may  be  placed  in 
the  proper  subgroup  of  the  stock  rocks,  making  Subgroups  lift  and  II & 
practically  continuous.  It  apjiears  from  Table  X  that  the  succession  of 
magmas  which  came  up  through  the  vertical  fissures  was  from  a  basic  one 
to  more  and  more  acid  ones,  and  that  the  previous  intrusions  which  formed 
the  sheet  rocks  were  of  a  magma  of  medium  chemical  composition. 

The  variations  of  the  other  chemical  constituents  of  these  rocks  are 
beet  comprehended  by  comparing  their  molecular  proportions.  This  has 
been  done  graphically  in  the  accompanying  diagram,  fig.  2,  in  which  the 
molecular  proportions  of  the  principal  oxides  are  plotted  as  ordinates,  those 
of  the  silica  being  taken  as  abscissas.  The  origin  of  abscissas  is  located 
some  distance  to  the  left. 

The  first  impression  derived  from  the  diagi'am  is  that  of  the  irregularity 
of  the  variations  in  all  the  oxides  besides  silica,  especially  in  the  magnesia. 
Moreover,  these  variations  appear  t(i  be  independent  of  one  another.  But 
this  apparent  independence  disappears  on  closer  study.  The  most  striking 
evidence  of  connection  between  the  molecular  proportions  exists  in  the  case 
of  the  two  oxides  of  iron;  the  ferrous  and  ferric  oxides  are  noticeably 
inversely  proportional  to  each  other,  an  increase  of  ferrous  oxide  being 
accompanied  by  a  decrease   of  ferric  oxide.     The  total  amount  of  iron 


MOLECULAR  VARIATION  OF  ELECTRIC  PEAK  ROCKS.  HiJ 

varies  iiTo<>ularly,  decreasing  from  the  basic  to  the  acid  end  of  the  series. 
While  each  of  tlie  iron  (^xides  is  quite  independent  of  the  magnesia,  it  is 
found  upon  reducing  all  the  iron  to  the  ferrous  state  that  there  is  the 
greatest  accord  between  the  iron  and  the  magnesia,  both  varying  in  like 
directions  and  to  nearly  the  same  extent.  The  ]nagnesia  drops  rapidly  at 
first,  and  is  very  erratic  in  the  more  siliceous  end  of  the  series,  where  it 
becomes  very  low. 

The  most  regular  variation  is  in  the  lime,  which  decreases  steadily  from 
the  basic  to  the  acid  end  of  the  series.     It  exhibits  little  or  no  connection 


AbQiJjaf  ^-^ 


OSiOz  .03&  UaSU^ 

Fig.  2. — Molecular  variation  of  the  rocka  at  Electric  Peak. 

with  the  other  constituents.  The  molecular  proportions  of  the  alumina, 
though  quite  irregular  between  certain  limits,  maintain  a  uniformly  high 
position,  and  are  much  greater  than  those  of  any  one  of  the  other  constitu- 
ents except  silica.  At  the  extreme  basic  end  of  the  scale,  however,  they 
are  equaled  by  those  of  both  the  magnesia  and  the  lime.  The  alkilies  are 
most  like  the  alumina  in  their  variations,  and  remain  very  nearly  uniform, 
increasing  somewhat  toward  the  acid  end  of  the  series.  The  soda  mole- 
cules are  more  than  twice  as  numerous  as  those  of  potash,  which  is  one  of 
the  most  noticeable  characteristics  of  the  rocks  of  this  locality.  In  the 
basic  end  of  the  series  the  alkilies  vary  together  in  the  same  direction. 


120  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

while  in  the  more  sihceous  end  they  vary  in  opposite  directions.  There  is  a 
marked  accordance  between  the  soda  and  the  alumina,  both  varying  in  the 
same  direction,  with  one  exception,  though  not  to  the  same  extent.  There 
is  a  more  strongly  marked  discordance  between  the  alumina  and  the 
magnesia,  which,  with  one  exception,. vary  in  opposite  directions. 

These  irregular  variations  take  place  not  only  among  allied  varieties  of 
rocks,  but  even  in  different  parts  of  one  and  the  same  rock  body.  They 
find  expi-ession  in  variations  in  the  proportions  of  the  essential  minerals. 

The  origin  of  this  variation  is  undoubtedly  to  be  sought  in  the  chemical 
differentiation  of  the  molten  magma.  The  development  of  the  constituent 
minerals  in  the  solidified  rock  is  the  result  of  physical  forces  that  combine 
the  chemical  constituents  of  the  magma  in  a  variety  of  ways  to  form  closely 
analogous  crystal  compounds.  A  discussion  of  the  possible  molecular 
condition  of  molten  magmas  will  not  be  taken  up  in  this  place.  A  few 
obvious  relations  between  the  mineral  and  chemical  variations,  however, 
may  be  pointed  out.  The  inverse  variation  between  alumina  and  magnesia, 
and  the  accordance  between  alumina  and  the  alkalies,  affect  the  relative 
proportions  of  feldspars  and  ferromagnesian  silicates,  which  vary  in  an 
inverse  ratio.  The  decrease  of  the  alkaline  earths  with  the  increase  of  silica 
and  the  alkalies  shows  itself  in  the  diminution  of  the  ferromagnesian  silicates 
and  the  calcium  feldspars,  which  accompanies  an  increase  in  quartz  and  the 
alkali  feldspars. 

The  reciprocal  variation  of  the  ferrous  and  ferric  oxides  indicates  the 
variable  oxidation  of  preexisting  ferrous  molecules.  This  should  naturally 
be  in  accord  with  the  development  of  minerals  containing  more  or  less  ferric 
oxide,  the  most  prominent  of  which  are  hornblende  and  liiotite.  Such  a 
coimection  seems  to  be  made  out,  but  data  for  its  complete  demonstration 
are  not  at  hand.  It  is  most  significant  on  account  of  its  bearing  on  the 
question  of  the  development  of  these  two  minerals  in  the  coarser-grained 
forms  of  rocks  whose  magmas  maj^  crystallize  under  other  conditions  free 
from  either  mineral.  It  may  tlu'ow  light  on  the  possible  action  of  water 
vapor  as  a  mineralizing  agent. 

The  order  in  which  the  constituents  crystallized  out  of  the  molten 
magma  to  form  diorite  may  be  learned  by  considering  the  relative  ages  of 
the  component  minerals.  It  has  been  pointed  out  that  some  crystallized 
almost  synchronously,  but  that  they  began  to  separate  from  the  liquid 


VOLCANIC  KOCKS  OF  SEPULCHRE  MOUNTAIN.  121 

magma  at  ditterent  times.  The  order  in  which  tlio  ditl'ereut  minerals  began 
to  crystalHze  in  that  portion  of  the  magma  which  formed  diorite  appears 
to  have  been  as  follows:  Magnetite,  liypersthene,  augite,  labradorite,  horn- 
l)lende,  biotite,  oligoclase,  orthoclase,  quartz.  The  feldspathic  minerals 
started  to  crystallize  liefore  an}-  of  the  ferromagnesian  minerals  had  com- 
menced; and  the  last  of  the  series  undoubtedly  crystallized  after  all  of  the 
feiTomagnesian  minerals  had  been  completed.  So  far  as  the  siliceousness  of 
the  minerals  is  concerned,  the  series  of  ferromagnesian  silicates  and  that 
of  minerals  free  from  iron  vary  in  opposite  directions.  In  the  former  the 
range  is  from  highest  silica  to  lowest;  from  the  metasilicate,  liypersthene,  to 
the  orthosilicate,  biotite.  In  the  second  it  is  from  the  least  siliceous,  labra- 
dorite, to  the  most  siliceous,  orthoclase,  or  to  free  silica,  quartz. 

THE  VOLCANIC  ROCKS   OF  SEPULCHRE   MOUNTAIN. 

The  igneous  rocks  of  Sepulchre  Mountain  are  partly  extrusive,  partly 
intrusive.  By  far  the  greater  mass  consists  of  subaerial  breccias  and  tuffs, 
with  a  small  amount  of  massive  lava  flows  The  intrusive  rocks  form  dikes 
and  larger  bodies  traversing  these  breccias.  The  breccias  and  flows  are 
andesites  of  various  kinds.  The  intrusive  bodies  are  andesites  and  dacite, 
grading  into  porphyry-like  modifications  in  places.  The  tuff-breccia  is 
separable  into  an  older  and  a  newer,  or  into  a  lower  and  an  upj^er,  l^reccia. 

THE    LOWER   BRECCIA.  , 

The  lower  breccia  is  about  500  feet  thick,  and  consists  mostl}'  of  frag- 
ments of  hornblende-mica-andesite,  and  is  generally  light  colored.  It  carries 
a  large  amount  of  fragments  of  crystalline  schists,  which  do  not  occur  in  the 
overlying  upper  Ijreccia.  It  is  probable  that  the  lower  breccia  was  ejected 
from  some  neighboring  center  of  eruption  located  in  an  area  of  Archean 
rocks.  Such  a  center  occurs  a  few  miles  north,  at  the  west  base  of  Sheep 
Mountain.  The  lower  breccia  passes  into  fine  tuff  in  places,  and  at  the 
extreme  end  of  the  northwestern  spur  of  the  mountain  it  is  distinctly  bedded, 
with  layers  containing  bowlders  of  a  rhyolite-porphyrj^,  which  has  not  been 
found  in  place  in  this  region.  In  places  the  upper  part  of  the  breccia  is 
green  and  partly  decomposed,  as  though  weathered  before  the  upper  breccia 
had  been  thrown  iq^on  it.  In  the  northwestern  spur  of  the  mountain  the 
upper  breccia  is  seen  to  rest  upon  an  uneven  surface  of  the  lighter-colored 


122  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

• 
bottom  breccia.     There  appears  to  have  been  a  distinct  time  break  between 

the  ejection  of  the  lower  breccia  and  that  of  the  upper  breccia.  The  occur- 
rence of  fragments  of  crystalHne  schists  in  the  bottom  Hght-colored  breccia 
and  their  absence  from  the  overlying  dark-colored  breccia  is  a  characteristic 
difference  between  these  two  breccias  wherever  they  have  been  observed 
along  the  northern  boundary  of  the  Yellowstone  Park. 

The  andesites  from  the  lower  breccia  at  Sepulclu-e  Mountain  vary 
somewhat  in  mineral  composition,  color,  and  microscopical  habit.  They  are 
mostly  light  colored — gray,  white,  and  red;  in  places  dark  colored.  Some 
fragments  have  comparatively  large  phenocrysts;  others  are  crowded  with 
small  ones.  The  greater  number  of  fragments  are  hornblende-mica-andesite ; 
some  have  little  mica,  and  grade  into  hornblende-andesite.  Others  are 
dacite,  having  quartz  phenocrysts.  The  microstructure  of  the  ground- 
masses  of  these  rocks  ranges  from  glassy  and  microlitic  to  microcrystalline. 
The  characters  of  the  minerals  and  the  microstructures  are  the  same  as 
those  of  the  light-colored  acid  breccias  on  the  Yellowstone  River  in  the 
neig'hborhood  of  Crescent  Hill,  and  also  those  in  the  vicinity  of  Cook 
City. 

It  is  important  to  note  that  there  is  associated  with  the  lower  acid 
breccia  of  Sepulcher  Mountain  an  obscure  body  of  massive,  vesicular  basalt 
with  porphyritical  augites  and  decomposed  olivines.  Its  exposure  is  of 
small  extent,  and  its  exact  relation  to  the  breccia  was  not  seen.  It  is 
ariiygdaloidal  with  quartz,  agate,  and  calcite.  It  does  not  resemble  the 
recent  basalts  in  the  neighborhood,  but  is  similar  to  basalt  associated  with 
the  bottom  acid  breccia  at  Crescent  Hill  and  in  the  valley  of  Cache  Creek. 
Its  petrographical  character  is  more  fully  discussed  in  Chapter  IX,  where 
it  is  classed  with  shoshonites. 

THE    UPPER    BRECCIA. 

The  upper  Ijreccia,  overlying  that  just  described,  is  dark  colored  at  its 
base  and  lighter  colored  in  the  upper  portion.  It  is  at  present  3,000  feet 
thick  through  the  summit  of  the  mountain.  The  lower  portion  consists 
almost  wholly  of  pyroxene-andesites,  with  little  or  no  hornblende.  Many 
fragments  are  vesicular  and  basaltic  in  habit,  without  megascopic  pheno- 
crysts. At  the  south  base  of  the  mountain  there  are  vesicular  massive 
bodies    of  pyroxene-andesite,    with   large    phenocrysts    of  pyroxene   and 


VOLCANIC  ROCKS  OF  SEPULCHRE  MOUNTAIN. 


123 


felds])!!!-.  The  u])per  portion  of  tliis  breccia  is  iiiore  hoi-iibleudic,  and 
horiil)k'iide-j)yroxene-;nul('sitcs  predominate.  The  transition  from  tlie 
pyroxene-andesite  ])ortion  to  the  liornl>U'nde-pyroxene-andesite  portion 
appears  to  he  <>ra(hi;d.  The  hiter  breccia  is  accom^janied  by  vesicular 
flows  of  simihu'  andesite,  often  cpiite  porous.  It  is  hghter  colored  in  gen- 
eral, but  parts  are  quite  dark,  witli  prominent  hornblendes,  the  habit  being 
andesitic,  not  basaltic.  There  are  no  evidences  of  any  considerable  In-eak 
or  interruption  between  the  higher  and  the  lower  parts  of  this  breccia. 
They  appear  as  a  continuous  geological  body,  composed  of  fragments  and 
flows  of  andesite  which  were  ejected  from  one  center  of  eruption  during  a 
considerable  period  of  time. 

The  andesitic  material  composing  this  breccia  varies  somewhat  in  min- 
eral composition  and  in  megascopical  habit,  as  will  be  seen  from  the  following 
descriptions.  The  variation  in  tlie  phenocrysts  present  other  than  feldspar 
in  the  specimens  examined  is  indicated  in  Table  XI.  They  are  andesites 
with  glassy  groundmass  and  phenocrysts  of  plagioclase,  hypersthene,  and 
augite  in  some  cases,  and  with  these  minerals  and  hornblende  in  others. 

Table  XI. — Mineral  variation  in  the  upper  breccias  of  Sepulchre  Mountain. 


I 

Mineral 
groups. 

Specimen 
uumber. 

Phenocrj'sts  other  than  feldspar. 

Pyroxene. 

Hornblende. 

Biotite. 

Quartz. 

1 
B,  ....\ 

B,  .... 
B,  .... 

385 
386 
387 
388 
390 
391 
392 
393 
394 
396 
397 
398 
400 
401 
402 
403 
404 

Much . 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Little 

Little 

Little 

Little 

Little 

Little 

1 

Some 

""{ 

Some 

Some 

Some 

124  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  XI. — Mineral  variation  in  the  iq)per  breccias  of  Sepulchre  Mountain — Cont'd. 


Mineral 
Group. 

Specimen 
number. 

Pbeuocrysts  other  than  feldspar. 

Pyroxene. 

Hornblende. 

Blotite. 

Quartz.         ' 

B^  .... 
Bs  .... 

405 
406 
407 
409 
410 
411 
412 
413 
414 
415 
416 
417 
418 
419 
420 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Some 

Some 

Some 

Some 

Some 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much 

Much : 

Much 

Little 

The  varieties  without  hornblende,  Bj — that  is,  pyroxene-andesites — 
have  a  groundmass  of  g-lobuUtic  brown  glass,  in  shades  from  dark  to  light, 
filled  with  microlites  of  feldspar,  pyroxene,  and  magnetite.  The  size  and 
abmidance  of  the  microlites  vary.  The  feldspar  microlites  are  plagioclase 
with  low  extinction  angles.  Two  of  the  varieties  examined  are  basaltic  in 
appearance,  with  a  few  decomposed  olivines  among  the  phenocrysts. 

The  pyroxenes  are  both  hypersthene  and  augite,  having  much  the  same 
general  appearance  in  the  same  rock.  Their  crystal  outline  varies  consid- 
erably in  one  rock  section.  Some  individuals  are  bounded  by  distinct 
crystal  planes,  while  others  are  rounded.  Some  have  irregularly  jagged 
outlines,  with  tongues  of  glassy  gTOundmass  ^^I'ojectiug  into  tlie  crystal. 
These  forms  appear  to  be  the  result  of  irregularities  of  growth  rather  than 
of  solution  by  the  magma  before  its  solidification.  Inclusions  of  glass  are 
common;  also  those  of  magnetite,  and  fewer  of  apatite. 

The  hypersthene  is  pleochroic;  green  parallel  to  C,  ^^ellow  parallel  to 
a,  light  red  parallel  to  h-  It  is  generally  light  colored  in  thin  section.  But 
one  darker-colored  crystal  with  strong  pleochroism  incloses  thin  brown 
plates,  aiTanged  in  lines  at  right  angles  to  the  vertical  axis  of  the  crystal. 
These  inclusions  are  like  those  in  hypersthene  in  many  coarsely  crystalline 


VOLCANIC  ItOCKS  OF  SKPULCUKE  MOUNTAIN.  125 

rocks.  In  tins  case  the  nxrk  is  f^lassy  and  vesicular,  and  shows  no  signs  of 
any  kind  of  nictainorj)hosin<i-  action.  The  inclusions  in  the  hypersthene 
appear  to  be  primary,  inclosed  at  the  time  of  the  crystallization  of  the 
mineral.  The  lighter-colored  hypersthenes  are  free  from  them.  Occasion- 
ally the  color  varies  in  concentric  zones.  In  some  rocks  both  kinds  of 
pyroxehe  have  naiTOw  reddish-brown  liorders  that  are  analogous  to  the 
black  borders  around  some  hornblendes,  and  appear  to  be  of  similar  origin. 
The  pyroxene  mien )lites  of  the  groundmass  are  aflFected  in  the  same  manner 
as  the  phenocrysts;  hence  the  change  of  condition  nmst  have  followed  the 
crystallization  of  the  microlites. 

The  color  of  the  augite  is  light  green  in  thin  section,  and  without  ple- 
ochroism.  It  is  like  the  augite  in  the  diorites  of  Electric  Peak,  both  optic- 
ally and  as  regards  cleavage.  Hypersthene  and  augite  are  occasionally 
intergrown  in  such  a  manner  as  to  indicate  their  nearly  synchronous  crys- 
tallization; but  when  one  incloses  the  other,  it  is  hypersthene  that  is  within, 
and  hence  the  older.  Hypersthene  is  the  more  easily  decomposed  of  the 
two,  and  changes  into  a  green  fibrous  mineral,  probably  bastite. 

The  feldspar  phenocrysts  are  all  lime-soda  feldspar,  and  are  mostly 
labradoi'ite,  judging  from  optical  characters.  Their  outline  in  sections  is 
rectangular,  sometimes  with  more  than  four  sides.  Zonal  structure  is  pro- 
nounced, but  the  difference  in  the  optical  character  of  the  various  zones  is 
not  marked.  Glass  inclusions  are  frequent.  In  the  larger  crystals  the 
central  portion  is  often  crowded  Avith  inclusions  of  brown  glass  containing 
the  same  microlites  as  the  surrounding  groundmass.  The  shape  of  these 
inclusions  is  usually  rectangular.  Many  smaller  feldspars  are  almost  free 
from  them.  Inclusions  of  magnetite  and  pyroxene  occur.  When  feldspars 
and  pyroxenes  have  crystallized  in  juxtaposition,  it  is  seen  that  the  feldspar 
is  the  younger,  but  that  its  crystallization  began  before  that  of  the  pyroxene 
ceased.     They  were  in  part  contemporaneous. 

Magnetite  occurs  as  microscopic  phenocrysts.  There  are  five  sections 
of  pyroxene-andesites  carrying  small  amounts  of  hornblende  and  consti- 
tuting transitional  varieties  between  these  rocks  and  hornblende-pyroxene- 
audesites. 

The  honablende  is  in  small  irregular  crystals,  some  being  rounded  and 
others  in  angular  shapes.  It  is  reddish  brown  and  brownish  green,  with 
strong  pleochroism.     Many  of  the  individuals,  especially  the  rounded  ones, 


126  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

have  a  narrow  border  of  magnetite  or  one  of  small  crystals  of  pyroxene, 
feldspar,  and  magnetite.  There  are  all  gradations,  from  rounded  horn- 
blendes with  opaque  borders  to  small  angular  pieces  of  hornblende  sur- 
rounded by  comparatively  large  crystals  of  pyroxene,  feldspar,  and  some 
magnetite,  which  form  a  group  of  interlocked  crystals  in  the  glassy  ground- 
mass.  The  angular  outline  of  the  hornblende  and  its  penetration  between 
the  crystals  of  feldspar  and  pyroxene  would  militate  against  the  supposi- 
tion that  the  hornblende  is  a  remnant  of  a  previous  crystal  that  had  been 
partially  resorbed  in  the  groundmass,  were  it  not  for  the  occurrence  in  one 
thin  section  of  a  group  of  different  crystals  with  a  hexagonal  outline,  cor- 
responding to  the  cross  section  of  the  hornblende  remnants  contained  in  it 
which  are  properly  oriented  for  such  a  section.  The  greater  part  of  the 
group  consists  of  feldspar  and  pyroxene  with  some  magnetite.  It  is  not  to 
be  supposed  that  these  minerals  crystallized  out  of  the  melted  hornblende 
substance  without  interchange  of  material  from  the  surrounding  magma. 
The  larger  groups  in  the  same  rock  section  exhibit  no  definite  outward 
form,  l)ut  are  bciunded  by  the  outlines  of  the  outer  crystals,  so  that  we 
may  conclude  that  the  process  of  resorption  of  the  hornblende  phenocrysts 
was  in  some  cases  accompanied  by  the  immediate  formation  of  grains  of 
magnetite  and  the  absorption  of  the  other  chemical  constituents  hj  the 
magma,  while  in  other  cases  the  melted  hornblende  recrystallized  in  situ  as 
pyroxene  and  magnetite.  But  in  the  instances  just  mentioned  the  partial 
resorption  of  the  hornblende  was  followed  b)'  a  greater  tendency  toward 
crystallization  in  the  magma  immediately  surrounding  the  melted  horn- 
blende, which  led  to  the  development  of  a  group  of  all  the  minerals  then 
capable  of  forming.  These  minerals  are  the  same  in  size  and  character 
as  the  small  crystals  scattered  through  the  glassy  groundmass. 

In  only  two  sections  of  the  andesites  examined  was  biotite  found.  It 
Avas  in  small  crystals  with  compound  borders  similar  to  those  flround  horn- 
blende. 

The  remaining  rock  sections  from  this  breccia  represent  hornblende- 
pyroxene-andesites  with  varying  amounts  of  the  ferromagnesiau  minerals, 
forming  a  series  with  increasing  hornblende  and  decreasing  pyroxene.  In 
these  andesites  the  microscopical  characters  of  the  pyroxenes  are  the  same 
as  in  the  rocks  just  described.     The  hornblende  varies  in  different  rocks, 


VOLCANIC  KOCKS  OF  SEPULCHKE  MOUNTAIN.  127 

both  in  color  and  in  the  extent  to  which  it  has  been  resorbed.  In  some 
cases  there  lias  been  no  resorption.  The  crystals  when  idionmrphic  are 
bounded  by  the  prism,  clinopinacoid,  and  the  usual  terminal  })lanes.  lu 
many  cases  the  form  of  the  crystals  is  not  sharply  defined.  The  color 
varies  from  intense  red  in  some  rocks  to  reddish  brown,  chestnut  brown, 
greenish  brown,  and  brownish  green,  with  the  corresponding  pleochroism. 
The  color  bears  no  fixed  relation  to  the  presence  or  absence  of  opaque 
border,  nor  to  the  amount  of  resorption.  It  does  not  appear  to  be  due  to 
secondary  alteration  of  the  hornblendes,  since  the  rocks  are  all  fresh  a)id 
glassy. 

The  character  of  the  border  is  not  always  constant  for  all  the  horn- 
blendes in  one  rock  section.  Around  it  in  some  cases  is  a  narrow  margin 
of  magnetite  grains ;  in  others  the  margin  is  heavy  and  opaque.  Other 
hornblendes  in  the  same  section  are  surrounded  by  crystals  of  pyroxene, 
plagioclase,  and  magnetite.  In  many  sections  all  the  hornblendes  are  alike, 
with  or  without  borders.  There  seems  to  be  no  relation  between  the  char- 
acter or  degree  of  resorption  and  the  degree  or  kind  of  crystallization  of 
the  groundmass ;  and  diff"erent  phases  of  resorption  occur  within  very 
short  distances  of  one  another  in  the  same  rock.  Crystals  which  do  not 
exhibit  other  signs  of  resorption  sometimes  have  large  "bays"  or  pockets 
of  groundmass  as  inclusions,  which  may  have  been  originally  inclosed 
at  the  time  of  the  crystallization  of  the  hornblende.  The  position  of 
the  hornblende  with  respect  to  adjacent  crystals  of  pyroxene  and  felds- 
par indicates  that  they  were  contemporaneous  crystallizations  in  part. 
The  latest  feldspars  and  pyroxenes  are  always  younger  than  the  horn- 
blende. 

The  feldspar  phenocrysts  are  all  plagioclase,  in  most  cases  labradorite, 
less  commonly  andesite  or  oligoclase.  Their  microscopical  characters  are 
very  nearly  the  same  as  those  of  the  feldspars  in  the  pyroxene-andesites. 
The  groundmass  of  these  andesites  in  some  cases  is  brown  globulitic  glass 
with  microlites  of  pyroxene,  feldspar,  and  magnetite.  In  most  sections  it 
is  coloi'less  glass  crowded  with  the  same  kinds  of  microlites.  It  carries 
microscopic  crystals  of  these  minerals  which  are  porphyritical  with  respect 
to  the  groundmass  when  seen  with  a  microscope,  but  which  in  turn  form 
part  of  the  groundmass  that  carries  the  megascopic  phenocrysts. 


128 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 


THE  DIKE  ROCKS. 

The  (like  rocks  of  Sepulchre  Mountain  are  andesites  and  dacites, 
the  earliest  of  which  resemble  the  pyroxene-andesites  and  hornblende- 
pyroxene-audesites  of  the  breccias.  Mineralogically  they  range  from  rocks 
with  phenocrysts  of  hypersthene,  augite,  and  lime-soda  feldspar  to  those 
with  phenocrysts  of  quartz,  biotite,  hornblende,  and  lime-soda  feldspar. 
This  variation  is  indicated  in  Table  XII,  in  which  103  sections  of  these  rocks 
are  arranged  according  to  the  proportions  of  the  porphj-ritical  minerals. 

Table  XII. — Mineralogical  variations  in  the  (like  rocks  of  Sepulchre  Mountain. 


Mineral 
group. 


D, 


D. 


D^ 


Speci- 
men 

num- 
ber. 


...< 


421 
422 
423 
424 
425 
426 
427 
428 
429 
430 
431 
432 
433 
436 
437 
441 
442 
434 
439 
440 
445 
446 
447 
448 
449 
451 
454 
456 
457 


Phenocrysts  other  than  fe'dspar. 


Pyrox- 
ene. 


Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Much. 

Some. 

Some. 

Some. 

Little. 

Little. 

Little. 

Little. 

Little. 

Li'otle. 

Little. 

Little. 

Little. 


Horn- 
blende. 


Biotite. 


Quartz. 


(?) 
Little. 
Little. 
Little. 
Little. 
Some. 
Some. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much.  I  Little. 
Much.  I  Little. 

Much.  I 

Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 


Trace. 
Little. 

Little. 


(*) 


Mineral 
group. 


D, 


Speci- 
men 
num- 
ber. 


De 


D,  .. 


452 
456 
443 
450 
453 
458 
459 
460 
461 
462 
463 
464 
465 
466 
467 
468 
469 
470 
471 
472 
473 
474 
475 
476 
477 
478 
479 
480 
481 


Phenocrysts  other  than  feldspar. 


Pyrox- 
ene. 


Trace. 
Trace. 
Little. 
Little. 
Trace. 
Little. 


Horn- 
blende. 


Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 
Much. 


Biotite. 


Little. 
Little. 
Little. 

Little. 


Little. 
Little. 
Some. 
Some. 
Some. 
Some. 
Some. 
Much. 


Quartz. 


DIKE  ItOCKS  OF  SKPULCHKB  MOUNTAIN.  129 

Tablb  XII. — Mineralogical  variations  in  the  dike  rocks  of  Sepulchre  Mountain — Cout'd. 


Mineral 
group. 

Speci- 
men 
num- 
ber. 

Pbeuocrysta  other  thau  feliUpar. 

Mineral 
group. 

Speci- 
men 
num- 
ber. 

Phenocrysts  other  than  feldspar. 

Pyrox. 

ene. 

Horn- 
bleude. 

Biotite. 

Quartz. 

Pyroi- 
eue. 

Horn- 
blende. 

Biotite. 

Quartz. 

482 
484 

Little. 

Much. 
Much. 

Much. 
Much. 



D,„.... 

504 
505 

Much. 
Much. 

Much. 
Much. 

Little. 
Little. 

485 

Much. 

Much. 

508 

Much. 

Much. 

Much. 

486 

Little. 

Much. 

Much. 

509 

Much. 

Much. 

Much. 

487 

Much. 

Much. 

510 

Much. 

Much. 

Much. 

488 

Much. 

Much. 

511 



Much. 

Much. 

Much. 

V,  .... 

489 

Much. 

Much. 

513 

Much. 

Much. 

Much. 

490 

Much. 

Much. 

514 

Much. 

Much. 

Much. 

491 

Much. 

Much. 

515 

Much. 

Much. 

Much. 

492 

Much. 

Much. 

D,,-- 

518 

Much. 

Much. 

Much. 

493 

Much. 

Much. 

519 

Much. 

Much. 

Much. 

494 

(?) 

Much. 

Much. 

512 

Some. 

Much. 

Much. 

495 

(?) 

Much. 

Much. 

516 

Some. 

Much. 

Much. 

D,.... 

496 

Some. 

Much. 

517 

Some. 

Much. 

Much. 

497 

Some. 

Much. 

520 

Some. 

Much. 

Much. 

500 

Much. 

Much. 

Much. 

Little. 

521 

Some. 

Much. 

Much. 

506 

Little. 

Much. 

Much. 

Little. 

522 

Some. 

Much. 

Much. 

507 

Little. 

Much. 

Much. 

Little. 

523 

Little. 

Much. 

Much. 

Dio 

498 

Much. 

Much. 

Little. 

524 

Little. 

Much. 

Much. 

499 

Much. 

Much. 

Little. 

D,.,.... 

525 

Little. 

Much. 

Much. 

501 

Much. 

Much. 

Little. 

526 

Little. 

Much. 

Much. 

502 

Little. 

Much. 

Little. 

527 

Little. 

Much. 

Much. 

503 

Much. 

Much. 

Little. 

Most  of  the  pyroxene-andesites  and  hornblende-pyroxene-andesites 
cany  uo  biotite.  In  a  few  cases  it  is  jjresent  in  small  amount.  Some 
homblende-andesites  contain  neither  pyi-oxene  nor  biotite;  others  have  a 
small  amount  of  both.  The  structure  of  a  glassy  pyroxene-andesite  dike 
rock  (421)  is  shown  in  PL  XXII,  fig.  1.  In  most  of  the  hornblende-mica- 
andesites  there  are  no  porjjhyritical  pyroxenes;  they  are  present  in  small 
amounts  in  a  few  cases;  and  they  are  equally  rare  in  the  dacites.  As  quartz 
phenocrysts  increase  in  number  biotite  is  more  abundant,  and  hornblende 
less  so.  Lime-soda  feldspars  are  present  in  all  the  rocks,  ranging  from 
labradorite  in  the  more  basic  andesites  to  oligoclase  or  andesine  in  dacite. 

The  microscopical  characters  of  the  minerals  are  the  same  as  in  the 
andesites  of  the  breccias.  The  pyroxenes  are  hypersthene  and  augite,  the 
first   being  more    readily  decomposed  and  sometimes  completely  altered. 

HON  XXXII,   PT  II 9 


130  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  hornblende  is  sometimes  represented  by  paramorphs  of  magnetite  and 
augite  in  the  pyroxene-andesites,  often  exhibits  black  borders  in  the  inter- 
mediate andesites,  and  in  the  more  acid  andesites  and  dacites  is  entirely 
free  from  any  dark  border.  Its  form  and  colors  are  the  same  as  before 
described  for  the  andesites  of  the  breccias.  Biotite  is  also  the  same  as  in 
those  rocks.     In  one  instance  it  incloses  a  small  crystal  of  plagioclase. 

The  feldspars  all  exhibit  polysynthetic  twnning.  Their  cross  sections 
are  mostly  rectangnlar  in  the  more  basic  andesites,  and  are  labradorite.  In 
some  of  these  andesites  they  appear  to  be  oligoclase.  In  the  more  acid 
andesites  and  dacites  the  lime-soda  feldspars  are  larger  and  have  more 
crystal  faces.  They  appear  to  belong  to  several  species.  Besides  numerous 
glass  inclusions,  there  are  a  few  instances  in  which  feldspar  phenocrysts 
contain  opaque  needles  and  grains,  arranged  in  several  systems  of  parallel 
lines,  which  are  identical  with  the  inclusions  in  many  of  the  labradorites  in 
the  diorite  of  Electric  Peak.  They  are  sometimes  accompanied  by  glass 
inclusions,  which  proves  their  primary  character.  Quartz  phenocrysts  are 
both  idiomorphic  and  rounded  in  the  same  rock  section.  They  usually 
occur  in  isolated  grains,  but  sometimes  several  are  attached  to  one  another 
(PI.  XXI  fig.  2),  just  as  several  feldspars  often  are.  Glass  inclusions  are 
abundant.  In  only  one  case  were  fluid  inclusions  noticed  together  with 
those  of  glass.  Magnetite,  apatite,  and  zircon  occur  in  their  usual  forms 
and  in  ordinary  amounts. 

The  groundmass  of  these  rocks  differs  in  degree  of  crystallization,  in 
mineral  composition,  and  in  structure.  In  the  more  basic  andesites  it  is  in 
many  cases  glassy,  with  multitudes  of  microlites  of  pyroxene,  plagioclase, 
and  magnetite;  in  many  others  it  is  completely  crystallized  and  the  out- 
lines of  the  microlites  are  no  longer  sharply  defined.  In  the  holocrystalline 
varieties  of  these  rocks  the  different  degrees  of  crystallization  may  be 
com23ared  with  one  another  by  arranging  them  in  a  table  according  to  the 
size  of  grain  of  the  groundmass.  This  has  been  done  in  Table  XIII,  in 
which  they  have  been  combined  with  the  specimens  of  breccia  fi-om  Sepul- 
chre Mountain,  and  have  been  separated  into  mineralogical  groups  whose 
scope  may  be  seen  by  comparison  with  Tables  XI  and  XII.  The  grades 
of  crystallization  correspond  to  those  established  for  the  intrusive  rocks  of 
Electric  Peak,  with  the  addition  of  five  more  grades,  which  embrace  two 
finer-grained  degrees  of  holocrvstalline  structure  and  three  degrees  of  glassi- 


U.  S.  OEOLOOICAL    SURVEY 


MONOOflAPH    XXXII     PART    II     PL.    XXII 


(B)  .  33 

PHOTOMICROGRAPHS    OF  PYROXENE-ANDESITE    AND    DACITE 


THE  HELIOTYPE  PRINTtNO  CO.,  BOSTON 


CRYSTALLIZAT'ox 


8i:PUL0HUB  MOUNTAIN  ROCKS. 


131 


ness.  Tlu'  rock  sliowii  in  I'l.  XXII,  fig'.  1,  belongs  to  grade  2,  being 
microlitir  glass.  In  the  dacite  shown  in  PI.  XXII,  fig.  2,  the  grade  of 
crystallization  is  it ;  and  in  the  dacite  shown  in  PI.  XXI,  fig.  2,  it  is  19. 

Table  Xlll. — (Jradex  of  cnjxtaUization  of  the  eruptive  rocks  of  Sepulchre  Mountain. 


B„  B,,  D„  D,. 

Ii„ii..B5.  I>3. 

V>t,  U„  D,. 

D„I>„D,. 

D,„,1),„D„. 

1. 

394,396 

416. 

2... 

385,  38fi,  387,  388, 
397,  398,  421, 
422,  423,  427, 
428. 

401,405,417 

459. 

3... 

390,  391,  392,  393, 
400,429. 

402,  403,  406,  407, 
409,  410,  411, 
412,  413,  418, 
431,  432,  433, 
434. 

4... 

404,414,415,  419, 

443,460,461,474.. 

476, 

420. 

5... 

445,462,463 

446,464,465 

481,  482,  496. 

477,484,485 

486,487... 

6... 

424 

436,437,439 

498  508  509 

7... 

425 

466,467,468,475.. 

499,  510,  511,  512, 
523. 

8  .. 

447  448  449  470 

478,  488,  489,  490. . 

500,  501, 502,  503, 
513,  514,  515, 

471, 472, 469. 

516,  ;i7,  524, 

525. 

9... 

451,  452,  453.  454. 
455. 

491,492,497 

.504  .518  tilQ 

10... 

11.. 

456, 457, 473 . , 

526, 

12  .. 

440 

479,  480. 

13... 

' 

505, 527. 

14... 
15... 

426 

441 

493. 

16... 

458 

494. 

17... 

18... 

520. 

506,  507, 521, 522. 

19 

495 

20... 

442. 

21... 

22... 

23... 

24... 

25... 

430.   . 

132     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  microstructiire  of  the  acid  varieties  is  not  the  same  as  that  of 
the  basic,  so  that  it  is  diflficult  to  compare  the  grain  of  one  directly  with 
that  of  the  other;  but  since  the  intermediate  rocks  230ssess  microstructures 
intermediate  between  these  extremes,  it  is  possible  to  estabhsh  a  kind  of 
relationship  between  them,  and  it  is  admissible  to  place  them  in  the  same 
line  across  the  table,  it  being  understood  that  the  correspondence  is  an 
a^jproximation. 

A  glance  at  Table  XIII  shows  that  a  large  majority  of  the  varieties 
are  very  fine-grained  forms  that  have  only  reached  the  crystallization  of 
the  few  smallest-grained  forms  of  the  Electric  Peak  rocks.  A  small  num- 
ber of  them  are  more  coarsely  microcrystalline  and  correspond  to  the  grain 
of  the  dike  rocks  at  Electric  Peak.  A  large  number  are  finer  grained  than 
any  of  these  rocks,  or  are  glassy.  The  coarsest-grained  forms  have  been 
attained  by  the  most  basic  varieties,  but  they  do  not  represent  bodies  of 
any  considerable  extent.  Specimen  No.  430,  grade  25,  comes  from  a  small 
exposure  with  no  definite  limits,  surrounded  by  much  finer-grained  rocks. 
It  is  properly  a  diorite-porphyry,  and  carries  much  biotite  of  final  consoli- 
dation, which  has  not  been  reckoned  with  the  phenocrysts.  The  coarsest- 
grained  forms  of  the  acid  varieties,  however,  represent  larger  bodies  and 
are  more  abundant  in  the  field. 

In  explanation  of  the  degrees  of  crystallization  indicated  in  the  table, 
it  may  be  said  that  the  first  three  are  glassy  groundmasses,  the  first  one 
having  fewer  microlites  than  the  second.  In  the  third  the  microlites  are 
closely  crowded  together.  The  next  two  represent  microlitic  structures  in 
which  no  glass  can  be  detected;  they  appear  to  be  holocrystalline.  In  the 
sixth  grade  the  form  of  the  microlites  is  more  indistinct,  but  the  general 
structure  is  the  same  as  before.  Beyond  this  the  diff'erent  deg-rees  indicate 
increasing  grades  of  a  structure  which  may  be  described  in  general  as 
follows:  Commencing  with  the  lowest  order,  the  groundmass  is  composed 
of  a  multitude  of  indistinct  microlites  of  lath-shaped  feldspars;  between 
crossed  nicols  this  aggregation  extinguishes  light  in  small  patches  Avhicli 
bear  no  fixed  relation  to  the  position  of  the  microlites  within  them.  As  the 
dimensions  of  the  lath-shaped  feldspars  become  larger  it  is  observed  that 
the  patches  of  light  and  darkness  arise  from  the  cementing  material  between 
these  feldspars.  This  cement  possesses  the  same  optical  orientation  for 
small  spaces  which  in  cross  section  produce  the  patches  just  alluded  to.     In 


CRYSTALLIZATION  OF  SEPULCHRE  MOUNTAIN  ROCKS.         133 

still  coarser-fjraiiied  fornis  it  becomes  apparent  that  the  cementing  material 
is  quartz  which  has  crystallizod  in  irregularly  shaped  patches  inclosing 
many  smaller  Feldspars.  The  size  of  thes(i  feldspars  and  of  the  interstices 
between  them  is  taken  as  the  grain  of  the  rock,  and  not  the  size  of  the 
patches  of  quartz.  For  it  is  observed  that  as  the  rocks  become  more 
coarsely  crystalline  the  felds[)ars,  which  are  plagioclase,  increase  steadily 
in  size  and  each  quartz  patch  cements  fewer  of  them,  until  in  still  coarser 
grades  the  quartz  forms  allotrioraorphic  individuals  between  the  plagio- 
clases  and  does  not  surround  any,  so  that  in  these  varieties  of  rock  the  size 
of  grain  is  judged  by  the  dimensions  of  the  plagioclases  and  the  interstices 
of  quartz.  The  patchy  structure  just  described  is  that  called  micropoikilitic. 
In  the  most  siliceous  varieties  of  the  rocks  the  microstructure  is  differ- 
ent. The  smallest-grained  forms  appear  to  approach  a  granular  structure, 
in  which,  however,  the  feldspars  exhibit  a  more  or  less  rectangular  shape 
and  the  quartz  shows  a  tendency  to  appear  in  minute,  poorly  defined 
dihexahedrons.  As  the  grain  becomes  larger  the  form  of  the  quartz  grains 
becomes  more  pronounced  (PI.  XXII,  fig.  2).  They  are  rudely  idiomorphic, 
with  sections  that  are  in  many  cases  equilateral  rhombs,  extinguishing  the 
light  parallel  to  their  diagonals.  In  the  coarsest-grained  forms  of  the  dacites 
these  imperfectly  idiomorphic  quartzes  are  characteristic  of  the  groundmass, 
and  reach  a  diameter  of  from  0.08  mm.  to  0.10  mm.  (PI.  XXI,  fig.  2). 
Their  surface  is  indented  with  the  ends  and  corners  of  small  plagioclases, 
the  structure  of  the  groundmass  being  hypidioraorphic.  These  quartzes 
often  contain  minute  colorless  inclusions  in  negative  crystal  cavities,  which 
have  every  appearance  of  being  glass  and  correspond  to  the  glass  inclusions 
in  the  quartz  phenocrysts  of  the  same  rocks.  The  partially  diomoi-phic 
quartzes  in  the  groundmass  are  to  a  slight  degree  porphyritical  with  espect 
to  the  other  constituents,  but  belong  to  the  final  consolidation  of  the  magma. 


134  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

GENERAL    CONSIDERATION    OF    THE    MINERAL    AND    CHEMICAL    COMPOSITION 
OF  THE  ERUPTIVE  ROCKS  OF  SEPULCHRE  MOUNTAIN. 

MINERAL    COMPOSITION. 

The  mineral  variations  in  tlie  group  of  rocks  forming  Sepulchre 
Momatain  are  much  simpler  and  require  much  less  discussion  than  those  of 
the  intrusive  rocks  of  Electric  Peak.  They  have  already  been  expressed 
in  Tables  XI  and  XII.  From  these  tables  it  is  evident  that  the  so-called 
transitional  forms  of  the  rocks  are  as  numerous  and  as  important  as  those 
forms  which  would  be  considered  type  rocks.  There  is  no  particular 
mineralogical  modification  of  the  rocks  at  this  place  which  from  its  gi-eater 
abundance  or  its  special  mode  of  occurrence  renders  it  a  type  rock.  On  the 
contrary,  the  whole  accumulation  of  eruptive  rocks  which  are  subsequent 
to  the  bottom  breccia,  with  its  admixture  of  Archean  fragments,  must  be 
considered  as  a  series  of  volcanic  rocks  that  vary  in  mineral  composition 
through  gradual  changes  from  pyroxene-andesite  to  dacite. 

Starting  with  those  rocks  which  carry  phenocrysts  of  pyroxene  and 
plagioclase,  it  is  observed  that  as  the  hornblende  makes  its  appearance  and 
increases  in  amount  the  pyroxene  decreases.  Biotite  accompanies  the 
hornblende  in  the  more  acid  varieties,  and  increases  in  amount  with  the 
acidity  of  the  rock.  Quartz  first  appears  in  small  quantities,  and  increases 
with  the  acidity  of  the  rock,  the  hornblende  decreasing  at  the  same  time. 
To  this  rule  there  are  exceptions,  which  are  indicated  in  the  table.  Biotite 
is  found  to  a  slight  extent  in  some  of  the  homblende-pyroxene-andesites, 
and  pyroxene  occurs  in  small  amounts  in  some  of  the  hornblende-mica- 
andesites.  It  is,  of  course,  understood  that  this  relation  between  the 
essential  minerals  may  be  different  for  groups  of  andesites  in  other  regions. 


CHEMICAL  COMPOSITION  OF  SEPULCUKE  MOUNTAIN  ROCKS.      135 


CHEMICAL   COMPOSITION. 

The  chemical  composition  of  the  ei-uptive  rocks  of  Sepulchre  Moun- 
tain is  shown  in  the  accompanying  table  of  chemical  analyses: 

Tablk  XIV, — Chemical  analyses  of  rocks  from  Sepulchre  Mountain, 


Constltaent. 

4«1 

471 

407 

386 

409 

487 

494 

521 

523 

SiOj 

55.83 
1.05 

17.11 

4.07 

3.75 

None. 

7.40 

55.92 

.94 

17.70 

3.16 

4.48 

Trace. 

5.90 

56.61 

.79 

13.62 

5.89 

2.60 

.35 

6.61 

.14 

5.48 

Trace. 

3.13 

2.71 

.06 

(?) 

None. 
2.27 

57.17 
1.03 

17.25 

2.48 

4.31 

None. 

6.61 

4.83 

Trace. 

3.44 

2.03 

.05 

Trace. 

Trace. 

1.20 

60.30 

.76 

16.31 

4.35 

1.41 

.13 

5.62 

.15 

2.39 

Trace. 

3.99 

2.36 

.20 

.10 

None. 
2.50 

64.27 

.32 

17.84 

3.36 

1.29 

None. 

3.42 

2.00 

.03 

3.84 

2.48 

.16 

Trace. 

None. 

L32 

65.50 

.45 

14.94 

1.72 

2.27 

.20 

2.33 

.13 

2.97 

Trace? 

5.46 

2.76 

.09 

.06 

None. 
L37 

65.66 
1.37 

15.61 

2.10 

2.07 

None. 

3.64 

67.49 

.13 

16.18 

1.30 

1.22 

.08 

2.68 

TiO. 

AljOa 

FesOa 

FeO 

MnO 

CaO 

BaO 

MeO 

5.05 

4.34 

2.46 

1.34 

SrO 

LiaO 

None. 

2.94 

1.71 

.21 

Trace. 

None. 

.09 

4.08 

2.28 

.18 

Trace. 

None. 

.36 

3.65 

2.03 

Trace. 

.13 

.12 

Na>20 

4.37 

2.40 

.13 

K2O 

P2O6 

SO3 

CI 

COi 

H20.. 

1.28 

1.42 

1.07 

2.69 

Less  0  for  01. 

100.  40 

100. 45 

100. 26 

100.40 

100. 57 

100.33 

100. 25 

100. 27 
.03 

100.  01 

100. 24 

Nos.  421,  471,  386,  487,  and  521  were  analyzed  by  Mr.  J.  E.  Whit- 
field; Nos.  407,  409,  and  494  were  analyzed  by  Dr.  T.  M.  Chatard;  and 
No.  523  was  analyzed  by  Mr.  L.  G.  Eakins. 

The  first,  421,  and  the  fourth,  386,  are  analyses  of  pyroxene-andesites 
which  carry  no  hornblende.  The  first  is  from  a  dike  near  tlie  summit  of 
the  mountain;  the  other  is  from  a  surface  flow  at  its  southwest  base. 
Nos.  407  and  409  are  of  hornblende-pyroxene-andesites,  occurring  as 
breccia  in  the  upper  part  of  the  mountain.  No.  471  is  of  hornblende- 
andesite,  which  is  an  intruded  body  in  the  small  hill  northeast  of  Cache 
Lake,  at  the  head  of  Reese  Creek.  No.  487  is  a  hornblende-mica-andesite 
from  the  same  locality,  also  an  intrusive  rock.  No.  494  is  the  same  kind  of 
andesite  from  an  intrusive  mass  at  the  north  base  of  Sepulchre  Mountain, 


136  GEOLOGY  OP  THE  YELLOWSTONE  JNATIONAL  PARK. 

and  Nos.  521  and  523  are  dacites  from  the  lidge  south  of  Cache  Lake.  The 
structure  of  521  is  shown  in  PI.  XXI,  fig-.  2. 

The  range  of  variation  in  the  percentage  of  sihca  is  about  the  same  as 
that  of  the  rocks  at  Electric  Peak.  The  character  of  the  variations  of  the 
other  oxides  in  these  rocks  is  shown  by  the  accompanying  diagram,  fig.  3, 
whicli  represents  the  variations  in  the  molecular  proportions  of  the  essential 
oxides,  and  has  been  plotted  in  the  manner  already  described. 

A  glance  at  this  diagram  shows  that  it  has  the  same  form  as  that  of 
the  group  of  analyses  of  the  rocks  from  Electric  Peak.     The  variations  in 


M,i03J60i 


CkLO  132 
M^-IZG 


Fig.  3 — Molecular  vari.ition  of  the  rocks  of  Sepulchre  Mountaiu. 

the  oxides  other  than  silica  are  quite  irregular  for  a  gradual  change  in  the 
silica.  The  alumina  varies  rapidly  in  2Dlaces  and  retains  a  high  position  in 
the  diagram.  The  alkalies  gradually  increase  with  the  silica,  the  soda  mole- 
cules being  twice  as  numerous  as  those  of  potash,  and  their  variations  being 
alike,  with  one  exception.  Magnesia  varies  most  widely,  and  in  striking 
contrast  to  the  alumina;  in  each  instance  they  vary  in  opposite  directions. 
The  lime  is  nearly  as  irregular  as  the  magnesia,  both  decreasing  rapidly 
from  the  less  siliceous  to  the  more  siliceous  end  of  the  series.  The  two 
oxides  of  iron  are  strikingly  reciprocal  in  their  variations,  the  significance 
of  which  has  been  pointed  out  in  discussing  the  diagram  for  Electric  Peak. 


IGNEOUS  ROCKS  WEST  OF  GALLATIN  MOUNTAINS.  137 

III  the  group  of  analyses  from  Sepulchre  Mountain  the  oxidation  of  the 
iron  bears  a  noticeable  relation  to  the  presence  of  hornblende,  biotite,  and 
magnetite  in  the  rocks. 

From  a  study  of  these  analyses  it  is  evident  that  the  chemical  varia- 
tions in  this  group  of  rocks  are  the  same  in  character  and  extent  as  those 
in  the  intrusive  rocks  of  Electric  Peak.  Moreover,  it  appeal's  that  the 
variations  between  similar  varieties  of  andesite — such  as  those  between 
dirtVrent  ])yroxene-andesites — are  as  great  as,  and  in  some  cases  greater  than, 
the  variations  between  varieties  of  andesites  which  are  distinguished  mineral- 
ogically  from  one  another.  Thus,  Nos.  421  and  386  are  pyroxene-andesites 
without  hornblende,  Nos.  407  and  409  are  hornblende-pyroxene-andesites, 
while  No.  471  is  a  hornblende-andesite.  It  is  not  possible  to  point  to  any 
chemical  character  of  these  rocks  that  is  distinctive  of  this  mineral  varia- 
tion, with  the  exception  of  the  oxidation  of  the  iron,  which,  though  slight, 
is  an  important  one ;  for  it  undoubtedly  relates  to  forces  that  did  not  alter 
the  fundamental  relation  between  the  bases  in  the  magma,  but  simply 
modified  it  by  changing  the  oxidation  of  one  of  them.  The  last  four 
analyses  are  of  hornblende-mica-andesites  and  dacites.  The  chemical  varia- 
tions between  them  are  as  pronounced  as  those  between  the  more  basic 
members  of  the  series,  without  there  being  the  con-esponding  differences 
between  the  kinds  of  ferromagnesian  silicates,  so  far  as  it  can  be  detected 
microscopically.  They  all  carry  hornblende  and  biotite,  and  no  pyroxene, 
the  relative  proportions  of  these  minerals  varying.  The  character  and 
amount  of  the  feldspars  differ  in  these  rocks,  and  so  do  the  abundance  and 
mode  of  occurrence  of  the  quartz.  In  Nos.  521  (PI.  XXI,  fig.  2)  and 
523  quartz  appears  as  pheuocrysts;  in  the  other  rock  it  is  confined  to  the 
groundmass. 

THE  EXTRUSIVE  IGKEOUS   ROCKS  WEST  AND  SOUTHWEST   OF  THE 

GAIiLATlN  MOUNTAINS. 

These  are  mainly  tuff-breccias  of  andesite,  with  rarely  a  massive  lava 
flow  of  andesite,  more  numerous  flows  of  basalt,  and  the  great  rhyolite  lava 
sheet.  Andesitic  breccias  form  the  north-south  i-idge  west  of  the  headwaters 
of  Fan  Creek,  and  extensive  accumulations  of  these  rocks  underlie  rhyolite 
in  the  northwestern  corner  of  the  Park,  where  they  are  connected  with  the 
range  of  volcanic  mountains  farther  north.  There  are  other  isolated  areas 
of  andesitic  breccia  in  the  gneissic  mountains  west  of  Mount  Holmes.     In 


138     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

all  of  these  localities  the  tufF-breccias  have  the  same  genei-al  character  as 
the  tuff-breccia  of  Sepulchre  Mountain,  just  described  They  vary  some- 
what in  compactness.  In  all,  the  fragments  are  small.  The  general  color 
is  dark,  but  that  of  the  individual  fragments  is  varied — dark  and  light 
grays,  with  tones  of  red.  There  are  abundant  small  phenocrysts  in  most 
instances;  some  fragments  are  almost  free  from  them,  while  others  carry 
larger  and  more  prominent  ones.  The  mineral  composition  varies  slightly 
among  the  fragments  in  any  considerable  mass.  The  greater  part  are 
hornblende-pyroxene-andesites  and  pyroxene-andesites.  Hoi-nblende-andes- 
ites  without  pyroxene  are  less  abundant.  Still  less  frequent  are  hornblende- 
mica-andesites,  representing  the  most  siliceous  rocks,  while  the  least  siliceous 
are  olivine-bearing  pyroxene-andesites  or  andesitic  basalts,  which  are  much 
rarer.  These  -s'arieties  naturally  grade  into  one  another  and  are  inter- 
mingled in  the  tuff-breccias. 

The  microscopical  characters  of  the  various  andesites  from  these  local- 
ities correspond  to  those  of  the  Sepulchre  Mountain  andesites.  The  ground- 
masses  range  from  glassy  to  microcrystalline  and  microlitic.  Some  of  the 
glasses  are  colorless,  others  brown  and  globulitic.  The  hornblendes  in 
most  cases  are  brown  and  reddish  brown,  seldom  green  (543),  which  con- 
trasts them  with  those  in  the  andesite-^Dorphyries.  They  often  have  black 
borders,  especially  in  the  more  basic  rocks,  where  they  are  sometimes 
paramoi'[3hosed  to  magnetite  and  pyroxene.  The  feldspars  are  plagioclases, 
more  calcic  in  the  less  siliceous  rocks.  They  are  characterized  by 
numerous  glass  inclusions  and  marked  zonal  structure.  The  pyroxenes 
are  hypersthene  and  augite.  The  olivine  in  two  rocks  where  it  was 
observed  is  serpentinized. 

COMPARISON  OF  THE  ROCKS  FROM  EIjECTRIC  PEAK  AlVD  SEPUIiCHRE 

MOUNTAIN. 

The  geological  structure  of  Electric  Peak  and  of  Sepulchre  Mountain 
and  the  occurrence  and  character  of  the  igneous  rocks  in  each  locality 
having  been  desci'ibed,  it  remains  to  point  out  the  relationship  of  the  two 
groups  of  rocks  to  each  other  and  the  petrological  deductions  which  may  be 
drawn  from  their  investigation. 

To  arrive  at  the  relationship  of  the  volcanic  I'ocks  of  Sepulchre  Moun- 
tain to  the  intrusive  rocks  of  Electric  Peak,  it  is  necessary  to  observe,  in 
review  of  the  facts  already  presented,  that  the  latter  cut  through  Cretaceous 


CORUELATION  OF  THE  ItOUKS.  139 

shales  and  sandstones,  and  have  imparted  to  tliem  sufficient  heat  to  meta- 
nior])h()se  tliein  for  a  fj-reat  distance,  indicating-  the  ])assa<'e  of  large  (juanti- 
ties  of  molten  magma  through  the  fissures,  while  the  lavas  of  Sepulchre 
Mountain  i-est  on  Cretaceous  strata  and  also  caiTy  large  blocks  of  black 
shale  inclosed  within  them  They  plainly  show  by  their  crushed  and 
dragged  portions  that  a  ])rofound  fault  has  separated  the  block  of  Sepulchre 
Mountain  from  that  of  Electric  Peak,  drojjping  the  former  down  consid- 
erably more  tlian  4,000  feet.  Consequentlv  the  volcanic  rocks  of  Sepulchre 
Mountain  once  occupied  a  higher  elevation  than  the  present  summit  of 
Electric  Peak  and  its  bodies  of  intrusive  rock. 

In  Electric  Peak  there  is  a  system  of  fissures  that  radiate  outward 
toward  the  south  and  southwest,  as  shown  by  the  dikes  of  porphyry.  At 
the  west  base  of  Sepulchre  Mountain  there  is  a  system  of  dikes  and  intruded 
bodies  that  radiate  outward  toward  the  north  and  northeast.  These  fissures 
antedate  the  great  faulting  just  mentioned  and  represent  the  east  and  west 
halves  of  a  system  of  fissui-es  trending  from  north  and  south  around  to 
northeast  and  southwest,  which  crossed  one  another  at  the  point  where  the 
broadest  body  of  intruded  rock  is  now  found.  The  axis  of  this  system 
appears  to  have  been  inclined  toward  the  east — that  is,  to  have  dipped 
toward  the  west — and  was  cut  across  by  the  great  fault  which  dropped 
Sepulchre  Mountain. 

The  igneous  rocks  that  broke  through  the  strata  of  Electric  Peak 
consist  of  a  series  of  andesite-porphyries,  occurring  in  sheets  between  the 
strata,  and  another  seiies  of  diorites  and  andesite-porphyries  that  were 
erupted  through  the  vertical  fissures  just  alluded  to.  The  central  fissure 
or  fissures  became  the  conduit  through  wdiich  the  molten  magmas  followed 
one  another  after  successive  intervals  of  time.  In  the  outlying  naiTow 
fissures  the  magmas  solidified  as  dikes  of  porphyry,  while  within  the  heated 
conduit  they  consolidated  into  coarse-gi-ained  diorites  of  various  kinds.  The 
magmas  of  this  series  of  eruptions  became  more  and  more  siliceous.  Their 
succession  is  indicated  in  the  table  on  the  next  page. 


140     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  XV. — Order  of  eruption  of  the  rocks  at  Electric  Peak  and  Sepulchre  Mountain. 


Succession  of  ernptioDs  at  Electric  Peak. 

Snccession  of  ernptions  at  Sepulchre  Monntain. 

A.  Intrusion   of  sheets   of   andesite-por- 

A.  Extravasation  of  andesitic  breccia  from 

phyry  from  the  southwest. 

some  Archean  area. 

B.  Intrusion  of  dike  and  stock  rocks  in 

B.  Eruption    of   andesitic   breccias    and 

the  following  order: 

dikes  in  the  following  order: 

Pyroxene-porphyries,  grading  into 

Pyroxene-audesites,  breccia,  and  do  ws, 

passing  into 

pyroxene-  and  hornhlende-diorites 

pyroxeue-hornblende-andesites,  brec- 

with biotite  of  tin.al  crystallization, 

cia,  and  flows,  with  dikes  of  similar 

with  dikes  of  pyroxene-  and  horn- 

andesites, grading  into 

blende-porphyries,  grading  into 

hornblende-biotitediorites  with  bio- 

hornblende-biotite-andesites, in  dikes, 

tite  of  early   crystallization,   with 

grading  into 

dikes  of  hornblende-biotite-porphy- 

ries  J 
quartz-  biotite-diorite-porphyry  with 

dacites  with  phenocrysts  of  quartz, 

some    hornblende,    with    dikes    of 

biotite,  and  some  hornblende. 

quartz-biotite-porphyry. 

The  igneous  rocks  that  formed  the  breccias  and  lava  flows  of  Sepulchre 
Mountain,  with  their  dikes  and  larger  intruded  bodies,  constitute  a  series  of 
andesites,  basalts,  and  dacites,  which  reach  a  degree  of  crystallization  that 
places  part  of  them  among  the  porphyries.  They  commenced  with  an 
andesitic  breccia  that  is  filled  with  Archean  fragments,  which  must  have 
been  thrown  from  some  neighboring  center  of  eruption  located  in  an 
Archean  area.  Such  a  center  exists  a  few  miles  to  the  north.  This  was 
followed  by  a  series  of  magmas  that  were  at  first  somewhat  basic  and  became 
more  and  more  siliceous.  The  series  is  represented  in  the  right-hand  column 
of  Table  XV.  From  this  it  is  seen  that  the  succession  of  eruptions  in  each 
locality  was  the  same  after  the  first  period.  A,  in  which  the  magmas  evi- 
dently came  from  different  sources.  Each  series  of  the  second  period  began 
with  basic  magmas  and  ended  with  acid  ones.  Their  division  in  the  table 
into  four  groups  is  not  intended  to  convey  the  idea  that  they  belong  to  four 
distinct  periods  of  eruption;  the  whole  series  in  each  case  is,  rather,  a 
single  irregularly  interrupted  succession  of  outbursts  of  magma  that  grad- 
ually changed  its  composition  and  character.  Upon  comparing  the  rocks 
which  have  resulted  from  the  corresponding  phases  of  these  series  of  erup- 
tions, the  similarity  of  the  porphyritic  forms  is  immediately  recognized. 


CORRELATION  OF  THE  KOGKS.  141 

Tlie  nature  and  distribution  of  the  phenocrysts  in  the  different  varieties  of 
andesite  and  dacite,  which  determine  their  inegascopical  habit,  liave  their 
exact  counterpart  in  the  different  varieties  of  porphyries.  The  microscopical 
characters  of  the  phenocrysts  in  the  corres})onding  varieties  of  porphyries 
and  of  the  intruded  andesites  and  dacites  are  identical  The  character  of 
the  various  groundmasses,  however,  is  different  in  tlie  two  groups,  being 
more  highly  crystalline  in  the  porphyries — many  of  the  andesites  being 
glass}'.  Many  of  the  tiner-grained  diorites  have  a  habit,  derived  from  the 
distribution  of  the  ferromagnesian  silicates  and  larger  feldspars,  which 
resembles  that  of  some  of  the  andesites  and  dacites  that  correspond  to  them 
chemically. 

Finally,  the  study  of  the  chemical  composition  of  the  intrusive  rocks 
of  Electric  Peak  and  of  the  volcanic  rocks  of  Sepulchre  Mountain  proves 
that  these  two  gi'ouj)S  of  rocks  have  identical  chemical  compositions,  for 
the  varieties  that  have  been  analyzed  are  but  a  few  of  the  many  miner- 
alogical  and  structural  modifications  assumed  by  these  magmas  on  cooling. 
The  analyses  serve  as  indications  of  the  range  of  the  chemical  variability 
of  these  magmas 

From  the  geological  structure  of  the  region,  then;  from  the  corre- 
spondence between  the  order  of  eruption  of  the  two  series  of  rocks;  from 
the  resemblance  of  a  large  part  of  the  rocks  of  both  series,  megascopically 
and  microscopically,  and  from  the  chemical  identity  of  all  the  rocks  of 
both  groups,  it  is  conclusively  demonstrated  that: 

I.  The  volcanic  rocks  of  Sepulchre  Mountain  and  the  intrusive  rocks 
of  Electric  Peak  were  originally  continuous  geological  bodies. 

II.  The  former  were  forced  through  the  conduit  at  Electric  Peak 
during  a  series  of  more  or  less  interrupted  eruptions. 

III.  The  great  amount  of  heat  imparted  to  the  surrounding  rocks  was 
due  to  the  frequent  passage  of  molten  lava  through  this  conduit. 

We  have,  then,  in  this  region  the  remnant  of  a  volcano,  which  has 
been  fractured  across  its  conduit,  faulted,  and  considerably  eroded,  and 
which  presents  for  investigation,  on  the  one  hand,  the  lower  portion  of  its 
accumulated  debris  of  lavas,  with  a  part  of  the  upper  end  of  the  conduit 
filled  with  the  final  intrusions,  and  on  the  other  hand,  a  section  of  the 
conduit  within  the  sedimentary  strata  upon  which  the  volcano  was  built. 


142  GEOLOGY  OF  THK  YELLOWSTONE  NATIONAL  PARK. 


CORRELATION  OF  THE  ROCKS  ON  A  CHEMICAL  BASIS. 

Correlatiuy  the  two  groups  of  rocks  according  to  their  chemical 
composition  and  arranging  them  as  in  Table  XVI,  we  see  that  the 
hornblende-mica-andesites,  Nos.  487  and  494,  are  the  equivalents  of  the 
quartz-mica-diorites,  Nos.  313,  311,  303,  323,  and  321,  and  of  the  quartz- 
pyroxene-tnica-diorite,  No.  309.  The  dacites,  Nos.  521  and  523,  are  the 
equivalents  of  the  quartz-mica-diorite-porphyries,  Nos.  329  and  326.  The 
hornblende-pyroxene-andesites  and  the  pyroxene-andesites,  Nos.  421,  471, 
407,  386,  and  409,  are  the  equivalents  of  the  coarse-grained  pyroxene-mica- 
diorite.  No.  295,  with  variable  percentage  of  quartz,  and  of  the  fine-grained 
diorites,  Nos.  272  and  273,  and  of  a  fine-grained  variety.  No.  267. 

The  dacites  and  hornblende-mica-andesites  included  within  this  cor- 
relation are  intruded  bodies  within  the  breccia  of  Sepulchre  Mountain,  and 
have  the  same  nrineral  conijiosition  as  the  corresponding  porphyries  and 
diorites  of  Electric  Peak.  They  diff'er  from  them  in  structure  and  degree 
of  crystallization,  as  already  described. 

The  glassy  andesites,  with  pyroxene  and  hornblende  phenocrysts, 
however,  present  the  utmost  contrast  to  the  chemically  equivalent  coarsely 
crystalline  diorites.  In  the  former  the  hypersthene,  augite,  hornblende,  and 
plagioclase  are  sharply  defined  idiomorphic  crystals  in  a  groundmass  of 
glass,  which  is  crowded  with  microlites  of  plagioclase  and  pyroxene,  besides 
grains  of  magnetite.  The  hornblende  is  brown,  occasionally  red,  and  the 
other  phenocrysts  have  all  the  microscopical  characters  which  distinguish 
their  occurrence  in  glassy  rocks.  In  the  diorite  the  hornblende  is  green;  in 
some  cases  brown  ;  and  the  hypersthene,  augite,  and  hornblende  are  accom- 
panied by  biotite,  and  are  all  intergrown  in  the  most  intricate  manner,  with 
evidence  that  they  commenced  to  crystallize  in  the  order  just  given.  The 
labradorite  is  often  clouded  with  minute  opaque  particles,  which  are  charac- 
teristic of  its  occurrence  in  many  diorites.  It  is  surrounded  by  a  shell  of 
more  alkaline  plagioclase,  which,  with  occasional  individuals  of  orthoclase 
and  considerable  quartz,  closed  the  crystallization  of  the  magma.  Magne- 
tite, apatite,  and  zircon  are  the  accessory  minerals.  The  quartz  contains 
fluid  inclusions,  which  complete  the  correspondence  of  this  diorite  with 
typical  diorites  of  other  regions. 

From  the  structure  of  this  region,  which  has  been  so  finely  exposed 


CHEMICAL  COHRkLATION  OF  THE  ROOKS. 


143 


by  faultiiiji'  aiul  erosion,  it  is  evident  tluit  of  the  diflFerent  magmas  enipted 
a  part  found  tlieir  way  into  vertical  fissures  and  took  the  form  of  dikes; 
part  reached  tlie  surface  and  became  hiva  flows  and  breccias,  while  other 
portions  remained  in  the  conduit.  Therefore  the  various  portions  of  the 
miio-nias  solidified  under  a  variety  of  physical  conditions  imposed  by  the 
dirt'erent  geological  environment  of  each,  the  most  strongly  contrasted  of 
which  were  the  rapid  cooling  of  the  surface  flows  under  very  slight  pressure 
and  the  extremely  slow  cooling  of  the  magmas  remaining  within  the  conduits 
under  somewhat  greater  pressure. 

Table  XVI. — Correlation  of  the  two  groups  of  rocks  upon  a  chemical  basis. 


S'O, 

No. 

Volcanic  rocks  of  Sepulchre  Mountain. 

Intrusive  rocks  of  Electric  Peak. 

Essential  minerals. 

Name. 

Name. 

Essential  minerals. 

Phcnocrysts. 

Groundroass. 

69.24.. 

67.54.. 

67.49.. 

66.05.. 
65.97.. 

65.66.. 

65.60.. 

65.50.. 

65.11.. 

64.85.. 
64.27.. 

64.07.. 

326 

321 
523 

323 
329 
521 

303 

494 

311 

313 

487 

309 

quartz  mica-diorite- 
porpbyry. 

quartz-mica-diorile . 

quartz-raica-diorite . 

quartz-mica-diorite- 

porphyry. 

quartz-mica-diorite  . 

quartz-mica-diorite  - 
quartzmica-diorite  - 

quartz-pyroxene- 

mica-diorite. 

quartz,  biotite,  plagioclase 
and  alkali  feldspar,  horn- 
blende. 

biotite,  hornblende,  plagio- 
clase (ortboclase),  quartz. 

biotite,  hornblende,  plagio- 
clase (ortboclase),  quartz. 

biotite,  hornblende,  plagio- 
clase (ortboclase),  quartz. 

biotite,  hornblende  (pyrox- 
ene),  plagioclase    (ortbo- 
clase), quartz. 

biotite,  hornblende,  augite, 
byperstheue,  plagioclase 
(ortboclase),  quartz. 

hornblende,  biotite,  plagio- 
clase (ortboclase),  quartz. 

biotite,  hornblende,  augite, 

hypersthene,    magnetite. 
plagioclase     (ortboclase) , 
quartz. 

(lacite 

quartz,  biotite,  horn- 
blende, plagioclase. 

holocrystalline, 
quartz,     feld- 
spar. 

dacite 

quartz,  biotite,  horn- 
blende, plagioclase. 

holocrystalline, 
quartz,     feld- 
spar. 

hornblende- 
mica  ande- 

site. 

hornblende,     biotite, 
plagioclase. 

holocrystalline, 
quartz,     feld- 
spar. 

horn  bleu  de- 
mi  ca-ande- 
eite. 

hornblende,      biotite, 
plagioclase,      mag- 
netite. 

holocrystalline, 
quartz,     feld- 
spar. 

144  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  XVL — Correlation  of  the  two  groups  of  rocks  upon  a  chemical  basis — Continued. 


SiO. 

"Volcanic  rocks  of  Sepulchre  Mountain. 

Intrusive  rocks  of  Electric  Peak. 

per 

No. 

Essential  minerals. 

cent. 

Name. 

Name. 

Essential  minerals. 

Phenocrysts. 

Groundmasa. 

61.22 

272 

pyroxene-mica  -  dio- 

rite. 

biotlte,  hornblende,  augite, 
hypersthene,    magnetite, 

' 

plagioclase  (quartz). 

60.30.. 

409 

horn  blend  e- 

pyroxene- 
andesite. 

hornblende,      augite, 
Lypersthene,  plagio 
clase,  magnetite. 

glassy,     micro- 
litic. 

58.05.- 

273 

pyroxene-mica  -  dio- 
rite. 

hiotite,  hornblende,  augite, 
hypersthene,    magnetite. 

plagioclase  (qiiartz). 

57  38 

267 

pyroxene-porphyry. 

augite,  hypersthene.  l)io- 
tite,     magnetite,     plagio- 

clase, quartz. 

57.17.. 

386 

pyroxenc- 

augite.    hyperstbene, 

brown        glass. 

aiidesite. 

plagioclase.                        niicrolitic. 

56.61.. 

407 

bornblende- 
pyroxene- 

bornblendf.      augite.     glassy,      niicro- 
hyperstbene,  plagio-  1      litic. 

andesite. 

clase. 

pyroxene-mica-dio  - 
rite. 

hiotite,  hornblende,  augite, 
hypersthene.    magnetite. 

plagioclase,  quartz. 

55.92.. 

471 

hornblende- 
andesite. 

hornblende,      plagio- 
clase. 

microcryatal- 
liue. 

55.83.. 

421 

pyroxeue- 
andesite. 

augite,    hyperathene, 
plagioclase. 

glassy,      niicro- 
litic. 

The  effect  of  this  diversit}'-  of  conditions  upon  the  degree  of  crystal- 
lization of  the  various  portions  of  these  rocks  is  well  shown  in  the  accom- 
panying Table  XVII,  which  has  been  derived  from  Tables  VIII  and  XIII. 

In  this  table  are  presented  all  of  the  specimens  from  Sepulchre  Moun- 
tain and  Electric  Peak.  They  are  arranged  in  four  principal  divisions: 
First,  the  breccias  and  lava  flows;  second,  dikes  and  larger  bodies intnided 
in  these  breccias;  third,  dikes  in  the  Cretaceous  strata  of  Electric  Peak; 
fourth,  the  main  stock  and  its  immediate  apophyses.  These  groups  are 
still  further  subdivided  into  columns  which  coirespond  to  mineralogical 
differences  in  the  rocks,  and  bear  the  same  letters  as  the  mineralogical 
subdivisions  in  Tables  III,  VIII,  XI,  and  XII.  Consequently  each  of 
the  four  principal  groups  has  the  most  basic  members  at  the  extreme  left 
and  the  most  acid  ones  at  the  extreme  right.  The  mineralogical  range  is 
therefore  repeated  four  times.  The  table  illustrates  a  number  of  facts.  It 
exhibits  the  relative  degree  of  crystallization  of  the  breccias,  lava  flows, 


Taiu.e  Wll. —Cornhilion  nj  ;/niittA  of  <n/stallhntioit  •>/  the  ruvkn  J'rvm  Seimkhrv  Mountain  and  Electric  i'eak. 


Gradtw  oT 

crystilliu- 

Udu. 

Sepulutira  MuuDlaiu. 

Electric  Teak.                                                                                                                                               1 

Breccias. 

Dike  nickS: 

Dikt,  rook*. 

StMkiwiki. 

B. 

394,396 

397,398 

400 

B. 

B. 

416 
417 
118 

4151,420 

D. 

D. 

1>> 

D. 

D. 

l>. 

D, 

u. 

D. 

D,. 

D„ 

Dit 

a, 

J. 

.u 

0. 

•1. 

d. 

.1, 

.1. 

a. 

<li. 

'k 

266 

j           267 

268 

269 

'           270 

H 

«3 

■4 

421,422.123 

427.428 
429 

4,59 

471 

416 

481, 482 

484, 4K5 

486, 487 

488,489,490 

191, 492 

496 

498 

499 

500, 501, 

608,509 

259 
260,261 
202, 263 

261, 2^ 

301 
302,303 

304 
305,306 

307 

2 

3 

385, 386, 387, 3fW 
390, 391, 392, 393 

401 
402, 403 

404 

405 

106,407,  109,410, 

411,412.413 

414,415 

■131,432,433, 
434 

443 

14i>  1            462, 463 
416  !            164,46^ 

6 

424 

436,437,439 

475 

177 

425 

466, 467. 46(1 

4611,470,471, 

472 

510, 611, 512 

513,514,515, 

516,517 

518, 519 

523 
521, 525 

■aa 

447, 448, 449, 

450 

461,452,453, 

454,455 

478 

■ 

497 

502, 503 
504 



241,212 

243 
244,245 

246 

256,256 
257 

258 

45U,  457 

473 

526 

440 

479,480 

239 

219,250 

251 

252,253 

13      ...  . 

505 

i>27 

.1. 

14 

426 

441 

493 

217,248 

IB 

18        .  .. 

458 

494 

236 

254 

17 

t 

18 

520 
521, 522 



19 

495 

506, 507 

232 

236,237 

20 

142 

333 

21 



326, 327 

328.329 

330,331 

332 

22 

!        -m 

272 
'    273,274 

23 

24 

310 

430 

234 

26 

275,276 

277 

■     278 

279 

280,281 

283,283 

284 

285,^, 

387 

288 

280 

308 

309 
310 
3.1 

...  1 

27 

318 

331 

28 

29 

30 

31 

' 

32 

33 

34 

35 

) 

36 

319 

320,321, 

286' 

290 

391 
394 
395 

296 
297 
298 
299 
390 

38 

312 

39 

313 

40 

275",322. 

41 

323 





1 



15 



j 



1 

1 

1 

1 



MON  XSXII,  I'T  II Face  page  144. 


CORRELATION  OF  THE  ROCKS.  145 

(likes,  and  stock  rocks,  and  shows  that  a  great  number  of  intermediate  steps 
can  be  recognized  between  the  most  ghissy  andesite  and  the  coarsest  diorite. 
It  shows  that  the  dike  rocks  furnish  the  connecting  link  between  these  two 
extremes,  and  that  the  dike  rocks  of  Electric  Peak  have  the  same  range  of 
grain  as  the  majority  of  those  of  Sepulchre  Mountain.  But  many  of  those 
at  Sepulchre  Mountain  are  still  finer  grained,  and  some  are  glassy,  being 
vesicular  also.  Between  these  rocks  there  is  the  closest  possible  resemblance 
megascopically,  and  the  two  groups  miglit  have  been  described  conjointly, 
so  far  as  their  })etrographical  characters  are  concerned.  The  variation  of 
grain  within  each  of  the  four  principal  divisions  is  very  significant  when 
taken  in  connection  with  the  geological  occurrence  of  the  different  rocks. 
The  limited  range  of  variation  in  the  first  group  is  in  accord  with  the  fact 
that  all  of  these  rocks  are  surface  ejectamenta.  The  range  in  the  third 
group  from  more  crystalline  basic  rocks  to  less  crystalline  acid  rocks,  as 
already  pointed  out,  shows  the  greater  tendency  of  the  basic  rocks  to 
crystallize.  And  since  the  dikes  here  represented  are  of  nearly  the  same 
size,  this  variation  of  grain  corresponds  to  differences  in  the  chemical  com- 
23osition  of  the  rocks.  On  the  contrary,  the  variations  in  the  second  group 
indicate  a  slightly  greater  crystallization  of  the  acid  rocks.  This,  however, 
is  dtie  to  the  fact  that  the  basic  rocks  in  this  group,  with  a  few  exceptions, 
occur  in  small  dikes,  while  the  acid  rocks  for  the  most  part  form  broad 
intruded  bodies  several  hundred  feet  wide.  In  these  cases  the  size  of 
the  mass  has  had  more  influence  on  the  degree  of  crystallization  than  has 
the  chemical  composition  of  the  magma.  In  the  fourth  group  the  basic 
rocks  exhibit  a  wider  range  of  grain  than  the  acid,  being  much  coarser 
and  also  considerably  finer  grained  than  the  latter.  This  arises  from  the 
fact  that  the  basic  rocks  form  a  much  larger  mass  and  exhibit  great  variation 
of  grain,  having  fine-grained  modifications  that  have  been  fully  discussed 
in  an  earlier  part  of  this  chapter. 

These  diorites  and  others  that  cut  the  volcanic  lavas  in  several  locali- 
ties in  this  region  correspond  to  the  andesdiorites  and  andesgranites  of 
Stelzner,  who  described  stocks  of  granular  rocks  penetrating  the  andesitic 
tuffs  in  Argentina.  The  study  of  these  Tertiary  granular  rocks  led  him 
to  the  conclusion  that  the  degree  of  crystallization  of  eruptive  rocks  is 
in  no  way  dependent  on  their  age,  but  depends  on  the  physical  conditions 

MON  XXXII,  PT  II 10 


146  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

under  which  the  nimeralogical  differentiation  and  the  cooling  of  the  magma 
took  place/ 

Study  and  comparison  of  the  chemical  analj^ses  of  the  two  groups  of 
rocks  under  investig-ation  demonstrate  that  the  magmas  that  reached  tlie 
surface  of  the  earth  in  this  place  had  exactly  the  same  chemical  compo- 
sition as  those  which  remained  inclosed  within  the  sedimentary  strata. 
They  prove  with  equal  clearness  that  the  different  conditions  attending  the 
final  consolidation  of  the  ejected  and  of  the  intruded  magmas  affected  nrA 
only  their  crystalline  structure,  hut  their  essential  mineral  composition.  The 
most  marked  illustration  of  this  is  in  the  occurrence  of  biotite  in  the  two 
series.  In  the  volcanic  rocks  of  this  locality  biotite  is  an  essential  constit- 
uent of  the  more  siliceous  varieties,  and  is  only  rarely  found  as  an  acces- 
sory constituent  of  the  varieties  with  less  than  61  per  cent  of  silica.  In  the 
intrusive  rocks  it  is  an  essential  constituent  of  all  the  coarse-grained  varie- 
ties, even  the  most  basic.  In  the  finer-grained,  porphyritic  forms  it  is  a 
constituent  of  the  groundmass  to  a  variable  extent.  The  second  most  notice- 
able difference  is  the  presence  of  considerable  quartz  in  the  coarse-grained 
forms  of  the  basic  magmas  and  its  absence  from  the  volcanic  forms  of  the 
same  magmas. 

From  these  observations,  then,  we  see  that  in  this  region  there  are 
chemically  identical  rocks  which  have  distinctly  different  mineral  compo- 
sitions, but  which  were  once  parts  of  a  continuous  body  of  molten  magma. 
We  are  led,  therefore,  to  the  conclusion  that — 

The  molecules  in  a  chemically  homogeneous  fluid  mayma  can  combine  in 
various  ivays,  and  form  different  associations  of  silicate  minerals,  producing 
mineralogically  different  rocks? 


'  Stelzner,  Alfred,  Beitriige  zur  Geologie  und  Paleontologie  der  Argentinischeu  Kepublik,  Cassel 
and  Berlin,  1885,  p.  207. 

"  Sie  [die  Andengesteine]  wird  uus,  wie  ich  meinerseits  glaube,  immer  mehr  uud  niehr  erkeoDen 
lassen  dass  die  grossere  oder  geringere  krystallinitat  ernptiver  Gesteine  keiiies  wegs,  wie  man  so  lange 
nnd  so  hartnackig  beliauptet  hat,  von  deui  Alter  der  letzteren  abhiingig  ist,  sondern  lediglich  von  den 
phvsikalischen  Umstiinden,  unter  deneQ  die  mineralische  Differeuzirung  iind  Erkaltuug  der  gluth- 
fliissigeu  Magmen  vor  sich  ging." 

'^This  conclusion  is  tbe  same  as  that  stated  by  Justus  Roth: 

"Es  kijnneu  mineralogisch  gauz  verschiedene  Gesteine  in  dieselbe  Gruppe  gehiiren,  denn  feurig- 
fliissige  Massen  von  gleieber  oder  sehr  uabe  gleicher  chemiscber  Zusammeusetzung  konnen  in  ver- 
schiedene Mineralien  auseinanderfallen.  Die  Ursachen,  welcbe  diese  Erscbeinung  bediugen,  lassen 
sich  bijchstens  muthmasseu  und  miigen  in  Unterschieden  des  Druckes,  der  Teniperatur,  des  ungebeiiden 
Mediums  der  Unterlage  u.  s.  w.  gesucht  werden."  Die  Gesteins-Analysen  in  tabellarischer  IJbersieht 
und  mit  kritischeu  Erlauterungen,  Berlin,  1861,  p.  xxi. 


CORRELATIOISr  OF  THE  KOGIvS.  147 

In  this  refj-ion  of  Electric  Peak  and  Sepulchre  Mountain  the  greatest 
minoralogical  differences  accompany  the  greatest  differences  in  structure  or 
degree  of  crystallization;  hence  we  may  assume  that  the  causes  leading  to 
each  are  coexistent.  The  source  of  these  caiises  must  be  soug-ht  in  the 
differences  of  geological  environment,  and  these  affect  the  rate  at  which 
the  heat  escapes  from  the  magmas  and  the  pressure  they  experience  during 
crystallization. 

It  is  to  be  remarked  that  the  most  essential  mineralogical  difference 
between  the  intruded  rocks  and  their  chemically  equivalent  extrusive  forms 
is  the  much  greater  development  of  biotite  and  quartz  in  the  intruded  rocks, 
these  minerals  being  abundant  even  in  the  basic  intrusions  and  absent  from 
their  basic  volcanic  equivalents.  That  their  simultaneous  development  is 
naturally  to  be  expected  in  many  cases  is  evident  from  a  consideration  of 
the  character  of  their  chemical  molecules  and  that  of  other  minerals  com- 
mon to  these  rocks.  For  if  we  assume  that  biotite  is  made  up  of  two 
molecules,  coiTesponding  respectively  to  KgAlgSieOai  and  Ri2Si6024,  and 
compare  these  with  the  molecules  of  orthoclase,  KgAlaSieOig,  of  olivine, 
RaSiOi,  and  of  liyperstheue,  RSiOg,  we  see  that  molecules  which  under 
some  conditions  might  have  taken  the  form  of  olivine  or  hypersthene  and 
potash  feldspar,  which  latter  may  have  entered  into  combination  with  lime- 
soda-feldspar  molecules  to  form  somewhat  alkaline  feldspars,  may  under 
other  conditions  combine  as  biotite  with  the  separation  of  free  silica  or 
quartz ;  in  which  case  also  the  feldspars  of  the  rock  would  be  less  alkaline. 

Another  mineralogical  difference  between  the  two  groups  of  rocks 
just  mentioned  is  the  greater  development  of  hornblende  in  the  intruded 
rocks  in  place  of  augite,  which  is  chemically  similar,  though  it  has  not 
been  determined  Avhether  in  this  case  the  hornblende  of  the  diorite  has 
nearly  the  same  composition  as  the  augite  of  the  andesite.  The  proba- 
bility is  that  there  are  considerable  differences  between  them. 

The  crystallization  of  quartz,  biotite,  and  hornblende  in  fused  magmas, 
according  to  our  present  knowledge,  requires  the  assistance  of  a  mineraliz- 
ing agent;  for  it  has  been  demonstrated  by  synthetical  research  that  these 
minerals  will  not  crystallize  in  the  forms  they  assume  in  igneous  rocks  when 
their  chemical  constituents  are  fused  and  simply  allowed  to  cool  under 
ordinary  atmospheric  conditions.  But  they  have  been  produced  artificially 
with  the  aid  of  the  mineralizing  action  of  water  vapor  and  of  other  gases. 


148  GEOLOGY  OP  THE  YELLOWSTOJSfE  NATIONAL  PARK. 

Now,  there  is  ample  evidence,  both  in  the  ejected  lavas  and  in  the  coarsely 
crystallized  rcicks  in  the  conduit,  that  water  vapor  was  uniformly  and  gener- 
ally distributed  through  the  whole  series  of  molten  magmas,  and  there  is 
no  evidence  that  there  existed  in  the  magmas  which  stopped  within  the 
conduit  any  more  vapors  than  those  which  existed  in  the  magmas  that 
reached  the  surface,  or  that  they  were  different  in  the  two  cases.  Hence 
we  conclude  that: 

The  efficacy  of  these  absorbed  vapors  as  mineraUsing  agents  was  increased 
by  the  conditions  attending  the  solidification  of  the  magmas  within  the  conduit. 

Moreover,  if  mineralizing  agents  are  universally  present  in  igneous 
mao-mas,  and  if  their  action,  so  far  as  we  can  observe  it,  is  controlled  by 
the  physical  conditions  imposed  by  the  geological  history  of  each  eruption, 
we  should  not  regard  the  presence  or  absence  of  certain  minerals,  relegated 
to  the  influence  of  mineralizing  agents,  as  evidence  of  the  presence  or 
absence  of  these  agents  in  the  molten  magma;  but  we  should  see  in  it  the 
evidence  of  special  conditions  controlling  the  solidification  of  the  magma, 
and  should  seek  the  fundamental  causes  of  the  mineralogical  and  structural 
variations  of  a  rock  in  the  geological  history  of  its  particular  eruption. 


CHAPTER    IV. 

DESCRIPTIVE   GEOLOGY  OF  THE   NORTHERN  END  OF  THE 

TETON  RANGE. 


By  Joseph  Paxson  Iddings  and  Walter  Harvey  AVeed. 


INTRODUCTION. 

The  Teton  Range  is  the  highest  and  most  imposing  of  the  mountain 
ranges  that  environ  the  Yellowstone  Park.  The  three  highest  peaks,  whose 
spire-like  summits  and  perpetual  snow  fields  are  visible  from  every  outlook 
of  the  Park,  form  a  well-known  feature  of  Wyoming  scenery,  giving  the 
mountains  the  familiar  name  of  the  Three  Tetons.  Only  the  northern  spurs 
and  lesser  peaks  of  this  range  occur  within  the  region  surveyed — that  is, 
north  of  the  forty-fourth  parallel  of  latitude.  This  northern  part  presents 
none  of  the  impressive  features  of  height  and  scenery  that  occur  in  the 
main  portion  of  the  range  farther  south,  yet  geologically  this  limited  area 
is  of  great  interest,  since  it  includes  the  northern  end  of  the  Ai-chean  nucleus 
of  the  range,  with  the  flexed  and  upturned  sedimentary  rocks  encircling  it. 
The  great  epochs  of  geological  time  are  all  represented  in  the  stratigraphic 
section  exposed  in  these  northern  peaks,  while  the  relations  of  the  eroded 
range  to  the  accumulations  of  basic  volcanic  breccias  and  to  the  great 
rhyolite  flows  of  the  Park  Plateau  are  here  revealed. 

The  area  shown  on  the  map  (PI.  XXIII)  includes  an  aecidented  region 
that  is  the  divide  between  the  waters  of  Falls  Ri-\-er  Basin  and  those  of  the 
valley  of  the  Snake.  The  two  most  ^jrominent  streams,  Owl  Creek  and 
Beny  Creek,  cut  deeply  into  the  uplifted  rocks,  exposing  Archean  gneisses 
and  the  overlying  Paleozoic  strata.  Two  prominent  summits,  known 
as  Survey  Peak  and  Forellen  Peak,  rise  above  the  general  level  of  the 
rhyolite  plateau.  The  region  is  well  wooded,  but  is  diversified  by  parks 
and  grassy  valleys  that  add  to  its  attractiveness.     The  recently  built  road 

149 


150     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

extending  southward  from  the  Upj^er  Geyser  Basin  and  the  Yellowstone 
Lake  to  the  southern  limit  of  the  Park,  and  the  wagon  trail  from  the  Mormon 
settlements  of  the  Falls  River  Basin  to  the  great  natural  meadows  of  Jack- 
son Lake,  make  the  region  readily  accessible. 

Sedimentary  series. — The  Sedimentary  rocks  begin  with  the  Middle  Cambrian, 
which  rests  directly  upon  the  crystalline  schists.     The  Sheridan  quartzite 
has  not  been  found  in  this  vicinity,  nor  have  any  beds  resembling  the  Algon- 
kian  been  noticed  in  the  area  mapped  as  Archean.     The  Paleozoic  includes 
beds  of  Silurian  and  Devonian  age,  whose  character  and  relations  appear  to 
be  the  same  as  those  of  like  age  in  the  Grallatin  Mountains.    The  Carboniferous 
series  presents  no  features  different  from  those  noted  in  the  northern  ranges. 
The  Juratrias,  on  the  contrary,  presents  a  far  greater  development  than  in  the 
Gallatin  Range,  and  its  typical  member,  the  Teton  sandstone,  forms  bright 
red  outcrops  that  are  especially  prominent  features  of  the  scenery  wherever 
exposed.     The  Ellis  limestones  appear  in  full  development  and  include  the 
impure,  shaly,  fossiliferous  beds  which  contain  an  abundant  marine  fauna, 
and  the  overlying  littoral  deposit  whose  character  varies  from  a  conglomer- 
ate or  coarse  sandstone  Avith  comminuted  shells  to  a  pure  crystalline  lime- 
stone.    The  Cretaceous,  as  noted  in  Chapter  V,  in  the  description  of  the 
region  lying  east  of  the  one  here  described,  is  essentially  a  series  of  sand- 
stones in  which  the  usual  subdivisions  are  not  readily  recognizable.     The 
Dakota  has  been  mapped  liy  the  occurrences  of  the  basal  conglomerate,  and 
the  Colorado  has  been  delimited  by  the  upper  belt  of  dark  shales  that  occurs 
in  the  sandstones.     The  Montana  group  is  represented  by  coarse   yellow 
sandstone,  containing  numerous  fossils.     The  Laramie  has  not  been  found 
in  the  exposures  of  this  locality,  but  is  probably  buried  beneath  the  rhyolite 
flows  of  Pitchstone  Plateau.     The  most  northern  extension  of  the  Teton 
Range  is  a  small  outlying  area  of  sedimentary  rocks  which  have  been 
upturned  by  the  dacite-porphyry  that  forms  the  summit  of  the  Birch  Hills, 
8  miles  north  of  Survey  Peak.     The  structure  of  the  Teton  region  shows 
that  it  is  the  end  of  an  anticlinal  uplift,  modified  by  faults  parallel  to  the 
axis  of  the  fold;  thus,  in  Forellen  Peak  the  crystalline  schists  have  been 
faulted  against  Carboniferous  beds,  a  small  area  of  the  Flathead  quartzite 
remaining  attached  to  the  gneissic  mass.     To  the  west,  in  the  amphitheater 
at  the  head  of  Conant  Creek,  Cretaceous  shales  have  been  faulted  agJiinst 
volcanic  rocks. 


us  GEOLOGICAL  SURVEY. 


MONOGRAPH  XXXII.PART  II.PL  XXIIl 


GEOLOGICAL  MAP 

OF 

THE  ^ORTHEKNT  END  OF  TETON  RANGE , YELLOWSTONE  NATIONAL  PARK. 

LEGEND 

PLEISTOCENE  CRETACEOUS  JURATRIAS  CARBONIFEROUS  DEVONIAN      SILURIAN 


Pal 

Pgd 

Kr 


Kc 


Kd 


Je 


Jl 


„,  ^^, , 

Cm 

Sj 


Anm-him         Glacial        Montmia       Colorado        I);ikola  EDis  Teton         Qujidiaiil       Madison      Threeforks      Jofler 

anil.        iormation.    formalion.     formation,    formation,     formation,    formation,    limeslone.     limestone,     limest 


son 
limestone. 


CAMBRIAN 


NEOCENE 


ARCHEAN 


1    €| 

€f       ; 

Nbst 

Nrh 

NIbb 

dp 

/Rgn 


GalJatin        l-'lallwad         Basalt.         Hltyolite.     Lalol)asii-       Dacite-       Granite  and       Faults 
nmestone.     fonnation.  breccia.      porpWiy.  giuiiss. 

Scale    125000 

^  T- ,_^^ 

CONTOUR  INTERVAL  lOO  FEET. 


NOUTHHKN  END  OF  TIOTON  RANGK.  151 


TOPOGKAIMIIC   FKATITRES. 

The  reffion  is  about  10  miles  wide  from  east  to  west,  and  7  miles  from 
north  to  south,  alon<>'  the  western  side  of  Snake  River  Valley.  The  highest 
point,  Forellen  Peak,  is  11, 700  feet  in  altitude,  while  others  of  9,200  and 
8,900  feet  occur  north  of  Berry  Creek.  The  district  is  almost  completely 
transected  by  two  deeply  cut  valleys,  those  of  ()\y\  an<l  Berry  creeks, 
flowing-  into  Snake  River.  The  extreme  western  side  of  the  mountains  is 
drained  by  Conant  and  Boone  creeks,  tributaries  of  Falls  River.  The  sides 
of  these  valleys  are  steep  and  exhibit  frequent  rock  exposures. 

The  valley  of  Owl  Creek  separates  the  mountain  region  situated  within 
the  limits  of  the  map  (PI.  XXIII)  from  the  main  range  lying  to  the  south. 
The  stream  has  cut  a  deep  gorge  at  right  angles  to  the  uplift,  heading  in  the 
Carboniferous  area  south  of  Forellen  Peak  and  on  the  slopes  of  Crimson 
Peak,  a  prominent  summit  that  reaches  10,300  feet  on  the  flanks  of  the 
range  south  of  the  forty-fourth  parallel  of  latitude.  That  portion  of 
the  gorge  which  is  cut  in  the  gneiss  to  a  depth  of  nearly  3,000  feet  shows 
steep  slopes  much  encumbered  with  the  debris  from  the  crest  of  the  ridge. 
Overlying  the  crystalline  schists,-  the  sedimentary  series  is  well  exposed  to 
the  east.  This  trench,  following  as  it  does  a  line  that  crosses  the  strike 
of  the  rocks,  appears  to  be  an  old  drainage  way  deflected  by  the  rhyolite 
capping  which  once  covered  this  area,  and  it  probably  marks  a  gulch  cut 
along  the  contact  between  the  rhyolite  sheet  and  the  underlying  rocks,  a 
contact  which  undoubtedly  crossed  varying  exposures,  as  the  country  was 
much  eroded  before  the  outflow  of  the  rhyolite. 

Berry  Creek,  which  heads  in  the  mountain  amphitheater  at  the  north 
base  of  Crimson  Peak  and  in  the  grassy  valley  lying  south  of  Survey 
Peak,  flows  with  a  general  easterly  course  4  or  5  miles,  then  turns  abruptly 
to  the  south  to  join  Owl  Creek,  leaving  what  is  clearly  the  old  drainage 
way  across  the  sedimentary  rocks,  but  which  is  now  occupied  by  a 
much  diminished  stream.  It  is  believed  to  have  been  diverted  by  a  small 
lateral  drainage  which  cut  back  until  it  robbed  the  stream  of  its  head- 
waters. Like  Owl  Creek,  this  stream  heads  in  the  Carbonifer(.)us  area  of 
the  western  part  of  the  mountains,  crosses  the  upturned  edges  of  the  Survey 
Peak  rocks,  flows  through  an  open  grassy  valley  cut  in  the  crystalline 
schists  and  across  the  basic  breccias  which  conceal  the  Paleozoic  beds  of 


152  GEOLOGY  OF  TIIP]  YELLOWSTONE  NATIONAL  PARK. 

the  valley  bottom,  and  passes  through  the  rhyolite  which  adjoins  the 
breccias  on  the  east. 

Both  Conant  Creek  and  Boone  Creek  head  in  deep  amphitheater-like 
basins,  which  have  been  cut  in  volcanic  tuff-breccia  and  easily  eroded  sedi- 
mentary formations,  the  rims  of  the  basins  being  formed  of  rhyolite  lava 
The  lower  portions  of  the  channels  are  canyons  cut  in  rhyolite. 

The  mountainous  portion  of  the  district  terminates  abruptly  on  the 
east,  along  the  banks  of  the  Snake  River,  while  outside  of  the  mountains 
the  country  stretches  northward  as  a  high  plateau,  with  ridges  reaching 
8,700  and  8,900  feet  in  altitude  near  Berry  Creek,  gradually  descending 
to  7,000  feet  hi  the  vicinity  of  Grassy  Lake  and  Bircli  Hills.  West  of  the 
mountains  long,  narrow  spurs  descend  somewhat  rapidly  to  the  level  of  Falls 
River  Basin  at  6,500  feet. 

With  this  brief  sketch  of  the  topographic  features  in  mind  we  may 
proceed  to  consider  the  geologic  structure  of  the  region,  beginning  with 
the  oldest  formations,  which  are  the  crystalline  schists. 

CRYSTAIiljINE   AXIS  AND  REGION  EAST. 

The  crystalline  schists  consist  of  light-pink  and  flesh-colored  gneisses 
and  smaller  amovints  of  mica-schists  and  amphibolites.  Together  they  form 
a  steeply  pitching  axis,  about  which  the  overlying  sedimentary  formations 
have  been  folded  and  broken.  The  most  northerly  exposure  of  the  gneisses, 
in  Berry  Creek,  is  not  higher  than  7,800  feet,  while  on  Forelleu  Peak  they 
reach  9,700  feet,  and  are  still  higher  in  the  mountain  south  of  Owl  Creek. 
In  the  mountains  on  both  sides  of  this  creek  the  crystalline  schists  are  seen 
to  have  an  almost  vertical  boundary  on  the  west,  along  the  fault  line  already 
mentioned.  On  the  slopes  of  lioth  these  mountains  steep,  narrow  gulches 
mark  the  plane  of  faulting  and  the  contact  between  the  schists  and  the 
nearly  vertical  limestone  beds.  This  plane  passes  through  the  summit  of 
Forellen  Peak  and  also  through  the  summit  of  the  peak  south. 

On  the  eastern  side  of  tliis  crj^stalline  axis  the  sedimentary  rocks 
overlie  it,  Avith  a  gradually  increasing  dip  toward  the  northeast.  On  the 
south  side  of  Owl  Creek  the  structure  is  the  same  as  that  of  Forellen  Peak, 
which  is  shown  on  the  map.  The  southern  side  of  the  valley  is  crystalline 
schists  nearly  to  the  summit  of  the  mountain,  the  eastern  portion  of  which  is 


BERRY  CREEK.  153 

covered  by  Flathead  qiiartzites  and  Paleozoic  limestones,  dipping  at  h^-w 
angles  toward  the  northeast. 

East  of  Forellen  Peak,  on  the  crest  of  the  mountain,  the  giieiss  is 
overlain  by  indurated  sandstones  having  a  strike  N.  55°  W.  and  a  dip  of 
20°  NK.  Lower  down  on  the  northern  side  of  the  ridge  light-gray  mottled 
limestones  are  exposed  in  a  nearly  vertical  position.  They  are  associated 
with  green  micaceous  shales  and  a  thin  layer  of  ferruginous  sandstone. 
Although  no  fossils  were  found,  there  is  little  doubt  that  the  beds  belong 
to  the  basal  portion  of  the  Cambrian.  A  short  distance  farther  east  the 
limestones  strike  N.  45°  W.,  and  dip  30°  E. 

The  crest  of  the  east  ridge  of  Forellen  Peak  and  the  eastern  slope  of 
tliC  mountain  are  covered  by  a  thin  sheet  of  lithoidal  rhyolite,  like  that 
forming  the  plateau  north  of  Berry  Creek,  of  which  it  is  unquestionably 
an  extension,  being  connected  with  it  across  the  bottom  of  the  valley. 
The  eastern  end  of  the  mountain  is  cut  off  by  the  canyon  tlxrough  which 
Berry  Creek  flows  to  join  the  Owl  Creek  drainage. 

East  of  the  gneiss  the  sequence  of  sedimentary  beds  is  quite  the 
same  as  that  observed  in  the  Survey  Peak  section,  to  be  described  (p.  160). 
The  relations  of  the  beds,  however,  are  partially  obscured  by  the  sheet  of 
rhyolite  just  mentioned. 

Berry  Creek. — In  tlic  canyou  of  Bcrry  Creek,  just  above  its  junction  with 
Owl  Creek,  the  sedimentary  rocks  are  well  exposed,  and  a  section  was  made 
which  shows  the  relative  thicknesses  of  the  Cambrian  rocks. 


Num- 
ber. 


Madison 


Section  of  sedimentary  roclcs  in  Berry  Creek  Canyon. 

Feet. 

■  22    Limestone,  crackled,  gray,  crystalline,  dense 25 

21    Limestone,  granular,  saccharoidal,  bull',  weathering  white 75 

20  Limestone,  magnesian,  gray  with  red  layers,  also  magnesian,  with  fossils  ..        50 

19    Limestone,  gray,  dense 10 

18     Limestone,  gray,  containing  patches  of  red  magnesian  rock 300 

,  17    Limestone,  gray,  containing  Carboniferous  fossils 2,  000 

riG  Limestone,  brown,  weathering  steely  gray,  with  fetid  odor  and  resembling 

™i        ,-,    1  Devonian ;  beds  arenaceous. 

Ihreerorks.  {  .                  ' 

15  Limestone,  thinly  V)edde(l ;  mottling  produced  by  irregular  bands  of  cream- 

l  colored  material. 

f  14    Limestone,  dark  gray ;  thinly  bedded,  few  feet "j 

Jefferson {  13  Limestone,  forming  great  ledge,  rough,  guttered,  and  pitted  surface;  no  )       150 

[  fossils,  except  at  top .__. J 

(  12    Limestone,  gray  with  sandy  patches _ 100 

Gallatin <;'  n     Shales,  gray  and  red 25 

LIO    Limestone,  forming  heavy  ledge;  brown  gray 50 


154 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 


Section  of  sedimentary  rocks  in  Berry  Creeh  Canyon — Continued. 


Flathead . 


Num- 
ber. 

9 


Feet. 

30 

2.T 


Shales,  with  thin  bands  of  limestone 

Shale,  green,  micaceous;  thin  bauds  of  limestone ^o 

Limestone,  light  gray ;  dense 15 

Limestone,  massive  ledge ;  lavender,  weathering  yellow 12 

Limestone,  gray,  weathering  yellow ;  splintered  vertically 5 

Shales,  micaceous,  calcareous,  green 5 

Limestone,  irregularly  and  thinly  bedded;  chocolate  colored 60 

Shales  f ;  poor  exposure 50 

Limestone,  thinly  bedded.    Strike  N.  50^  W.,  dip  35^  NE 35 

The   slope   of  the  peak  to  the   east  of  this  canyon  is  benched  in  a 
series  of  steps,  whose  upper  surface  corresponds  to  that  of  the  limestone 
beds,  but  exposures  are  few  and  unsatisfactory.     The  summit  of  the  peak  is 
fonned  of  the  cherty  Teton  sandstone,  resting  upon  the  white  Quadrant 
quartzites,  which  here  break  into  small  angular  fragments.     The  northern 
slope  of  this  peak  is  open  and  grassy  near  the  summit,  but  the  flanks  of  the 
mountain  are  thickly  covered  with  young  pines  and  fallen  timber.     At  the 
point  where  Berry  Creek  leaves  its  mountain  valley  to  flow  in  a  succession 
of  cascades  and  rapids  through  the  canyon  just  mentioned,  the  Juratrias 
rocks  are  well  exposed.     The  highest  beds  noticed  were  soft  and  micaceous 
shales,  which  occur  beneath  the  red  Teton  sandstones.     The  beds  strike  N. 
50°  E.,  and  dip  25'^  NW.     The  rocks  are  fissile  micaceous  shales,  contain- 
ino-  much  pyrite,  and  near  the  entrance  of  the  mountain  are  warped  and 
twisted  into  a  number  of  small  folds.     In  the  upper  part  of  the  canyon  the 
granular  white  limestones,  which  are  generally  buff  or  creamy  yellow  on 
fresh  fractures  and  belong  to  the  Quadrant  quartzite,  are  also  well  exposed. 
The  Quadrant  quartzite  series  is  underlain  by  a  streak  of  reddish  magnesian 
clays,  a  part  of  the  limestone  series  that  forms  the  highest  beds  of  the 
Madison  formation.     The  fossils  are  of  Lower  Carboniferous  age,  and  are 
most  abundant  above  the  hard  gray  limestones  which  alternate  with  the 

red  streaks. 

In  descending  the  creek  the  strike  gradually  changes  from  N.  50°  E. 
to  N.  30°  E.,  this  change  occurring  within  a  distance  of  half  a  mile.  Still 
farther  down,  the  strike  veers  rapidly  toward  the  west,  and  near  the  junction 
with  Owl  Creek  it  has  changed  to  N.  50°  W.,  which  is  the  general  strike 
of  the  strata  north  of  Owl  Creek,  both  above  and  below  the  mouth  of  Berry 
Creek.  Below  the  forks  the  arenaceous  fetid  limestones  of  the  Jefferson  for- 
mation extend  down  the  stream  until  lost  in  the  meadows  of  Snake  River. 


UILLS  WEST  OF  SNAKE  KIVEB.  155 

Althouf^h  the  rhyolite  lavas  of  the  Park  cover  and  conceal  the  higher 
series  of  strata  which  formed  the  flanks  of  the  Teton  uplift,  subsequent 
erosion  has  laid  l)are  a  narrow  area  immediately  west  of  the  Snake  River 
meadows  in  which  the  Mesozoic  beds  are  exposed.  The  attitude  of  the 
strata,  shows  that  they  form  an  anticlinal  fold  that  is  one  of  the  lesser 
flexures  of  the  northern  extension  of  the  Teton  uplift.  This  particular  fold 
has  a  north-south  axis,  pitching  about  5°  N.,  the  fold  dying  away  in  the 
region  covered  by  the  rhyolite  sheet. 

The  rocks  forming  the  peak  north  of  Owl  Creek,  whose  summit  has  an 
elevation  of  1,700  feet  above  Snake  River  meadows,  have  already  been 
noted.  East  of  this  peak  a  low  elevation,  Avliose  summit  is  but  7,200  feet, 
presents  excellent  exposures  of  the  Triassic  and  Jurassic  series.  The  basal 
cherty  arenaceous  limestones  of  the  Teton  fonnation  form  the  south  end  of 
the  hill  and  are  cut  by  the  small  stream  west  of  it.  The  summit  is  covered 
by  the  red  Teton  sandstones,  whose  detritus  is  abundant,  though  good 
exposures  are  rare.  These  sandstones,  which  are  the  representatives  of  the 
great  Red  Bed  series  of  Wyoming,  consist  of  lavender-colored,  pink,  and 
red  sandstones,  generally  fissile,  fine  grained,  and  weathering  to  sandy 
clays.  On  the  northeiTi  slope  of  this  hill  the  Teton  sandstones  are  overlain 
by  the  gray  argillaceous  limestones  and  calcareous  shale  beds  of  the  Ellis 
formation,  carrying  characteristic  Jurassic  fossils.  The  strike  is  N.  70°  E., 
and  the  dip  40°  N. 

Hills  west  of  Snake  River. — North  of  BciTy  Crcck  a  loug  aud  high  ridge  extends 
to  the  shores  of  the  Grassy  Lakes.  The  eastern  flanks  of  this  ridge,  extend- 
ing down  to  the  meadows  of  Snake  River,  form  benched  slopes  and  a  broken, 
hilly  country,  in  which  exposures  of  the  sedimentary  rocks  are  often  seen, 
though  the  surface  is  largely  covered  by  drift  and  is  overgrown  by  vegetation. 
The  Teton  formation  is  exposed  at  the  south  end  of  the  ridge,  a  deep  cut 
eroded  in  the  soft  sandstone  of  this  horizon  continuing  the  valley  of  Berry 
Creek  eastward.  Above  these  red  sandstones  the  gray  beds  of  the  Ellis 
formation  are  seen,  forming  the  8,500-foot  knoll  at  the  south  end  of  the  ridge. 
This  formation  presents  the  same  two  divisions  which  are  so  characteristic 
a  feature  of  its  development  in  the  Gallatin  Range.  The  lower  part  of  the 
series,  the  Ellis  limestone,  consists  of  thinly  bedded,  impure,  argillaceous, 
gray  limestones  and  lead-colored  calcareous  shale,  weathering  readily  and 
containing  an  abundance  of  fossils  of  characteristic  Jurassic  types.     These 


156  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

beds,  which  form  the  lower  and  greater  part  of  the  formation,  are  capped 
bv  the  arenaceous  hmestone,  whose  variable  nature  is  its  chief  characteristic. 
This  bed  varies  from  a  pure  white  or  gray,  rather  coarse  granular  limestone, 
composed  largely  of  broken  fragments  of  shells,  to  a  pure  sandstone  that  is 
occasionally  conglomeratic.  Near  the  base  the  bed  is  always  a  limestone 
and  contains  carbonaceous  remains  and  fossils  of  characteristic  Jurassic 
type.  The  indurated  nature  of  this  bed  makes  it  a  noticeable  feature.  It 
forms  good  exposures  and  affords  a  marked  horizon  which  aids  in  the 
working  out  of  the  geological  structure.  The  strike  of  N.  60°  E.,  noted  at 
8,150  feet  on  the  slopes,  varies  rapidly,  as  the  bed  shows  an  anticlinal  fold 
slightly  modified  by  small  local  flexures.  The  dip  varies  from  40°  to  55°. 
The  following  section  was  made  of  the  beds  exposed  at  this  locality: 

Section  in  hills  tcest  of  Snake  River. 

Sandstones;  soft,  lissile,  and  crumbly. 
r  Black  sbales.  T'eet. 

White  limestone 5 

Colorado.^  Black  shales 1*^ 

Sandstones,  ripple-marked  and  cross  bedded 50 

.  Black  carbonaceous  shale,  poorly  exposed 300 

rSaudstone;  soft  and  fissile 25 

Dakota..  I  Limestone  and  gray  and  purple  clays. 

'-  Sandstones. 
Ellis Limestone ;  arenaceous,  cross  bedded,  fossiliferous. 

The  uppermost  beds  of  this  section  are  exposed  about  a  mile  south  of 
the  mouth  of  Glade  Creek,  the  beds  having  a  strike  of  N.  50°  W.  and 

dipping  30°  N. 

The  Montana  formation  consists  largely  of  yellowish  sandstones, 
differino-  in  this  respect  from  the  character  prevailing  in  the  Gallatin  region. 
The  beds  form  a  small  but  steeply  sloped  hill  west  of  Glade  Creek,  near  its 
mouth,  being  exposed  in  a  bluff  150  feet  high  and  500  feet  long.  This 
exposure  shows  a  fault,  bringing  soft,  gray,  argillaceous  shales  against 
yellowish  and  gray  sandstone  carrying  abundant  fossils  of  Fox  Hills  types. 
The  latter  beds  strike  N.  10°  E.  and  dip  30°  W. 

Higher  up  the  creek  flowing  past  this  bluff  the  stream  has  cut  very 
soft,  thinly  bedded,  fissile,  light-colored  sandstones,  overlain  by  sandstones 
alternating  with  occasional  beds  of  shale.  No  fossils  were  seen  at  these 
exposures.  The  higher  slopes  are  everywhere  covered  by  the  soft  sandy 
debris  derived  from  the  sandstone,  and  no  exposures  are  seen.     In  general 


VOLCANIC  ROCKS  NORTH  OF  BERRY  CREEK.        157 

the  northern  slopes  are  mantled  by  this  material.  ^lany  of  the  bare  areas 
seen  on  these  slopes  show  no  rock  in  place,  but  are  due  to  the  washing-  out 
of  this  soft  drift  material.  The  hig'hest  strata  seen  consist  of  shale  and 
limestone,  exposed  back  of  the  rhyolite  hill  west  of  the  forks  of  Glade 
Creek. 

No  Laramie  rocks  were  identified,  but  it  is  probable  that  the  friable 
sandstones  carrying-  a  4-foot  seam  of  coal,  exposed  on  the  east  bank  of  the 
Snake  l)elow  the  mouth  of  Grlade  Creek,  are  of  this  age.  The  strata  at 
this  locality  strike  E.-W.  and  dip  35°  N.,  but  on  the  slope  above,  at  7,400 
feet,  the  beds  strike  N.  40°  E.  and  dip  25°  NW. 

Volcanic  rocks. — Tlie  eroslon  of  the  sedimentary  rocks  was  unquestionably 
very  great  before  the  extravasation  of  volcanic  material,  for  basic  andesitic 
tuif-breccia  is  found  in  the  bottom  of  the  valley  of  BeiTy  Creek,  resting  upon 
a  very  irregular  surface  of  crystalline  schist  and  Paleozoic  strata.  In  places 
it  contains  rounded  pebbles  of  gneiss,  with  some  of  andesite.  It  probably 
occupies  what  was  an  ancient  valley  draining  northward,  for  on  the  east  and 
west  of  it  sedimentary  rocks  rise  to  peaks  a  thousand  and  more  feet  higher 
than  the  present  lowest  exposure  of  breccia.  The  breccia  forms  a  group  of 
small  hills  and  knolls,  rising  500  feet  above  the  bottom  of  the  valley.  It  is 
overlain  by  massive  rhyolitic  lava,  which  also  covered  a  very  uneven  sur- 
face, being  at  present  600  to  800  feet  thick  above  the  breccia  and  1,500  feet 
thick  just  east  of  it,  where  it  seems  to  have  filled  a  depression  between  the 
hill  of  breccia  and  the  eastern  sedimentar}'^  ridge.  Toward  the  west  it 
thins  out  over  the  limestones  at  the  base  of  Si;rvey  Peak,  where  it  is 
glassy  and  porphyritic,  probably  the  bottom  part  of  the  sheet  which, 
farther  east,  is  lithoidal  and  thinly  laminated,  somev>^hat  resembling  schist. 
In  this  part  of  the  rhyolite  the  lamination  which  corresponds  to  the  planes 
of  flow  in  the  lava  dip  to  the  north,  indicating  that  the  lava  had  been 
moving  over  a  northward-sloping  surface. 

REGION  WEST  OF  THE  CRYSTAELINE  AXIS. 

West  of  the  fault  that  bounds  the  western  side  of  the  body  of  crystal- 
line schists  the  sedimentary  rocks  have  been  u^^turned  at  a  high  angle, 
causing  them  to  dip  steepl)^  at  about  80°  W.  for  a  short  distance,  beyond 
which  they  become  flatter.  This  structure  is  seen  in  the  mountain  south 
of  Owl  Creek  and  in  Forellen  Peak  and  Survey  Peak.     In  the  western 


158     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

summit  of  the  mountaiu  south  of  Owl  Creek,  steeply  upturned  limestones 
dip  80°  W.  and  appear  to  be  continuous  with  those,  to  be  described,  west  of 
the  summit  of  Forellen  Peak.  Directly  west  of  them,  on  the  di-vdde  south 
of  the  head  of  Owl  Creek,  massive  limestone  abuts  against  them  with  a  low 
easterly  dip.  These  are  the  eastern  portion  of  a  flat  anticlinal  arch,  whose 
axis  trends  north  along  the  western  side  of  the  amphitheater  at  the  head  of 
Owl  Creek.  The  western  portion,  with  slight  westerly  dip,  forms  the  ridge 
between  the  headwaters  of  Owl  and  Conant  creeks,  the  most  northerly  point 
of  which  is  Crimson  Peak. 

Crimson  Peak. — Here  thc  Strata  strike  S.  50°  W.  and  dip  7°  NW.  The 
dips  farther  down  the  northwest  spurs  varj^  from  7°  to  10°  in  the  same 
general  direction.  The  red  color  of  the  summit,  which  is  so  prominent 
when  the  mountain  is  seen  from  a  distance,  is  due  to  the  red  magnesian 
streaks  and  patches  Avhich  occur  in  the  higher  beds  of  the  Carboniferous 
limestones.  The  summit  of  the  peak,  which  is  10,300  feet  above  sea 
level,  shows  good  exposures  of  the  white  Quadrant  quartzites,  the  rocks 
weathering  in  great  cubical  blocks;  being  of  very  compact  texture,  they 
resist  erosive  agencies  and  are  in  striking  contrast  to  the  same  series 
exposed  near  the  junction  of  Owl  and  Berry  creeks.  Fossils  collected  from 
the  northeastern  spur  of  the  mountain  prove  to  be  of  lower  Carboniferous 
age.  Farther  down  the  spur,  on  the  saddle  of  the  divide  southwest  of 
Forellen  Peak,  a  horizon  of  fossiliferous  limestone,  carrying  peculiar  con- 
cretions of  chert,  occurs  above  a  brown  arenaceous  bed  that  is  correlated 
lithologically  and  by  its  stratigraphic  jjosition  with  the  Devonian  of  the 
Grallatin  section.  This  sandy  limestone,  which  is  believed  to  correspond  to 
the  Three  Forks  limestone,  is  underlain  by  fine-grained  and  dense  gray 
limestone,  Avhose  peculiar  rough,  pitted,  and  guttered  surface  makes  it  a 
readily  distinguishable  horizon.  This  bed  corresponds  to  the  Jefferson 
limestone  of  the  Gallatin  Range.  These  strata  continue  northward  along 
the  western  slope  of  Forellen  Peak,  having  a  low  dip  to  the  west.  They 
adjoin  the  nearly  vertical  limestones  that  have  been  faulted  against  the 
gneiss  in  the  same  manner  as  in  the  mountain  south  of  Owl  Creek. 

Forellen  Peak. — Ncarl)'  vcrtlcal  liuiestoues  form  the  western  summit  of  For- 
ellen Peak  and  the  steep  narrow  spur  down  its  northern  flank.  The  beds 
forming  the  summit  of  the  peak  are  Carboniferous,  and  100  feet  below 
them  stratigraphically  is  the  dark-gray  massive  limestone,  weathering  with 


SITRVKY  PEAK.  159 

guttered  surface,  that  has  just  lu'cii  noted.  'I'he  heds  liave  a  general  strike 
N.  35°  W.,  and  dip  «0^  8W.  Upon  the  gneiss,  directly  east  of  the  fault, 
there  is  Flathead  quartzite,  dipping  ;it  a  low  angle  toward  the  northwest. 
The  fissile  Cambrian  formations  liave  Ix'en  completely  displaced  at  this  point. 

The  displacement  noted  on  Forellen  Peak  jjrobably  diminishes  north- 
ward and  may  fade  out  east  of  Survey  Peak,  tlie  steeply  dipping  strata 
continuing  through  this  mountain  into  the  hills  north  of  it.  Here  the  light- 
gi'ay  and  brown  stri})ed  limestones  of  the  ^ladison  formation,  which  form 
the  naain  mass  of  Survey  Peak,  strike  N.  25°  W.  and  dip  70°  SW.  At  the 
eastern  base  of  the  mountain  they  have  the  same  strike,  but  a  lower  dip, 
about  25°  SW. 

Survey  Peak. — Ou  the  slopes  soutlieast  of  Survey  Peak  the  gneiss  is  well 
exposed,  immediately  overlain  by  the  rusty  Flathead  quartzite  with  strike 
N.  70°  W.  and  dip  15°  N.  Above  this  ledge  no  exposures  are  seen  for  50 
feet,  when  limestones  outcrop,  the  ledges  being  conformable  in  dip  and 
strike  to  the  quartzites  below.  These  limestones  are  dark  gray,  mottled 
with  butf  spots  of  sandy  material,  and  resemble  the  limestones  occurring 
in  the  Flathead  shales.  Above  these  beds  the  slopes  show  poorly  exposed 
limestones,  eroded  by  glacial  action  into  well-marked  benches.  Six  hundred 
feet  above  the  gneiss  the  beds  consist  of  chocolate-colored  cherty  lime- 
stones, alternating  with  gray  crystalline  limestones  containing  traces  of 
fossils  and  much  cut  up  by  veins  and  jjatches  of  calcite.  On  the  east  slope 
of  the  mountain  the  beds  are  well  exposed,  forming  rough,  bare  ridges 
devoid  of  soil  or  timber. 

The  best  section  of  the  Paleozoic  rocks  is  to  be  found  north  of  the 
creek,  in  the  slopes  which  fall  away  from  the  eastern  flanks  of  Survey  Peak. 
Here  we  have  a  continuous  series  of  beds  from  the  Archean  to  the  red 
shales  and  clays  of  the  Teton  formation.  The  section  given  on  the  next 
page  was  measured  at  this  point. 


160 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


dum- 
ber. 


Survey  Peak  section. 


Feet. 


Teton 18 

Quadrant  ...     17 

ri6 

15 

14 
13 
12 
11 

Madia,  m \  10 

9 


6 
5 

4 
3 

Three  ForkH  f  .,    ^ 
1 


Cherty  sandstone,  forming  slopes  of  Sur%ey  Peak. 
Quartzite,  white,  etc.,  forming  summit  of  peak. 

Limestone,  with  red  streaks,  etc.,  near  top 1,  000-|- 

Liniestone,  gray,  splintery 25 

Limestone,  brecciated 50 

Limestone,  gray,  similar  to  beds  below 50 

Limestone,  brown,  containing  peculiar  chert  balls 10 

Limestone,  cherty,  fossiliferous,  steely  gray 300 

Limestone,  gray,  weathering  brown,  with  smooth  surface 30 

Limestone ;  not  exposed 25 

Limestone,  gray  brown,  obscure  traces  of  fossi  Is 30 

Limestone ;  not  e.xposed 30 

Limi  stone,  dense,  gray 10 

Limestone,  brown,  with  rough,   guttered  surface.     Strike  N.   5-'  W. ;    dip 

30^'  W 100 

Limestone,  light  yellowish  green ;  laminated 10 

Limestone,  light  gray,  cherty 25 

Limestone,  dark  gray,  cherty.     .Strike  N.  10°  E. ;  dip  5=  W 10 

Limestone,  great  ledge  of  rough  brecciated  rock  at  base  of  east  slope  of 

the  peak 150 


The  summit  of  Survey  Peak  is  formed  of  the  cherty  sandstones  which 
occur  at  the  base  of  the  Teton  formation,  but  the  western  flank  of  the 
mountain  is  covered  by  a  narrow  strip  of  rhyohte  that  connects  the  rhyolite 
sheet  near  the  head  of  Berry  and  Conant  creeks  with  the  rhyohte  plateaus 
which  sweep  northward  to  the  geyser  basins.  This  rhyolite  west  of  the 
peak  is  about  one-fourth  of  a  mile  wide,  its  upper  limit  being  8,600  feet, 
and  it  forms  a  bench  terminated  westward  by  bold  cliffs,  some  200  feet  in 
height,  that  form  the  wall  of  the  Boone  Creek  amphitheater.  The  bottom 
of  the  sheet  dips  to  the  west.  The  surface  of  the  rhyolite  is  quite  irregular, 
as  tlie  sheet  rests  upon  the  steeply  upturned  Teton  shales  which  have 
slipped  beneath  its  weight,  forming  great  tissures  of  varying  width,  from  a 
few  feet  to  many  yards  across  and  often  many  yards  long.  Huge  masses 
have  become  detached  and  have  slid  down  to  the  bottom  of  the  amphi- 
theater valley.  To  the  south  the  rhyolite  thins  out  against  the  cherty 
sandstones,  but  on  a  projecting  point  extends  to  the  flat  summit  at  the  head 
of  Beny  Creek.  Beneath  the  rhyolite  the  walls  of  the  amphitheater  show 
the  red  Teton  shales  and  sandstones  well  exposed  and  dipping  steeply  to  the 
northwest.  These  Teton  sandstones  probably  extend  under  the  gravel- 
\capped  ridge  to  the  west,  but  no  exposures  were  seen. 


CON  ANT  OKEIiK.  161 

conant  Creek. — Tlu*  Cai'boniforous  limostones  of  Crimson  Peak  south  of  the 
head  of  Herry  Creek  extend  down  tlie  northern  spur  Avith  a  dip  of  7°  to  10° 
NW.,  as  ah-eady  stated,  and  form  the  divide  to  Conant  Creek  and  the  creek 
south  of  it;  but  the}'  are  covered  with  rhyoHte  farther  north,  appearing 
beneath  it  in  several  spurs  projecting  into  the  valley  at  the  head  of  Conant 
Creek,  llie  lower  portion  of  the  rhyolite  sheet  is  dark  coloreil  and  glassy, 
becoming  lighter  colored  and  lithoidal  higlier  up.  On  the  small  spurs  the 
lamination  of  the  lava  dips  to  the  northwest,  showing  that  the  slope  was  in 
this  direction.  On  the  divide  between  Conant  Creek  and  the  creek  south 
the  limestones  terminate  abruptly  against  soft  clays  and  sandstones,  pre- 
sumably of  Cretaceous  age,  but  of  which  there  are  no  good  exposures, 
while  to  the  south  the  massive  lime'^tones  can  be  traced  along  a  western 
escarpment  to  where  the}'  overlie  sandstone  and  gneiss,  which  form  a  group 
of  peaks  northwest  of  the  main  Teton  Range. 

The  soft  clay  shales  and  friable  sandstones  on  the  low  saddle  south  of 
the  head  of  Conant  Creek  dip  toward  the  west  and  extend  northward  across 
the  basin  at  the  head  of  Conant  Creek.  Their  close  proximity  to  the  Car- 
boniferous limestones  indicates  a  fault  and  considerable  displacement  between 
the  two,  which,  however,  nia}^  not  exist  farther  north;  for  west  of  Survey 
Peak  there  is  sufficient  distance  between  the  Teton  formation  and  the  north- 
ward extension  of  the  shales  to  allow  of  the  intermediate  formations  being 
in  place. 

The  divide  between  Conant  Creek  and  the  head  of  Boone  Creek  is  a 
narrow  ridge  composed  of  well-rounded  gravel,  mostly  quartzite.  This  also 
forms  the  lower  ends  of  the  two  short  spurs  south.  The  exact  relation  of 
this  gravel  to  the  adjacent  rocks  was  not  discovered.  Its  character  and 
geuei'al  appearance  are  those  of  a  recent  deposit  connected  with  the  glacia- 
tion  of  the  region. 

Volcanic  breccia. — The  sedimentar}^  area  is  bounded  on  the  west  by  an 
accumulation  of  volcanic  tuff-breccia  that  is  exposed  for  a  distance  of  6 
miles  north  and  south,  and  again  farther  north  in  the  neighborhood  of  Birch 
Hills.  The  actual  extent  of  the  breccia  is  unknown,  since  it  is  partially 
covered  by  rhyolite.  A  portion  of  it  has  been  uncovered  in  Berry  Creek. 
It  is  well  exposed  in  the  valleys  cut  through  it  by  Boone  and  Conant  creeks. 
The  rocks  exhibit  rude  assorting,  but  are  not  bedded,  the  coarse  agglomer- 
ates occui'ring  with  tuffs  and  fine  breccias  without  order  or  arrangement. 

MON  XXXII,  PT  II 11 


162  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  material  consists  of  basic  andesites  and  basalts,  some  of  which  are  absar- 
okite  and  contain  orthoclase  as  an  essential  constituent.  Petrographically 
the}'  are  like  tlie  basaltic  breccias  of  the  Absaroka  Range. 

The  breccias  are  dark  colored  and  often  weather  into  fantastic  towers, 
pinnacles,  and  cliffs,  whose  dark  rich  shades  of  red,  brown,  purjile,  and 
gray  render  them  highly  picturesque.  The  fragments  are  angular  and  sub- 
angular  and  often  are  several  feet  in  diameter.  The  best  exposures  occur 
just  l)el()w  the  amphitheater  at  the  head  of  Boone  Creek.  On  the  north 
side  of  Conant  Creek,  where  the  exposure  is  nearly  1,000  feet  high,  there 
are  indications  of  rude  bedding,  dipping  westward. 

The  breccias  were  thrown  upon  the  surface  of  deeply  eroded  and  faulted 
sedimentary  rocks,  and  undoubtedly  were  considerabl}^  eroded  themselves 
before  being  buried  beneath  the  rhyolite,  which  forms  the  western  slopes 
and  sjjurs  and  extends  beneath  the  later  basalt  sheets  of  the  Falls  River 
Basin  a  long  distance  westward.  The  canyons  of  Boone  and  Conant  creeks 
cut  into  it  400  feet  and  more  without  reaching  the  underlying  rocks.  The 
rhyolite  is  porphyritic  and  lithoidal  as  a  whole,  but  at  the  bottom  of  the 
sheet,  in  contact  witli  the  underlying  rocks,  it  is  dark-colored  obsidian. 

Birch  Hills. — The  Birch  Hills,  whose  summits  rise  prominently  above 
the  western  border  of  the  plateau,  present  the  most  northern  exposures 
of  the  sedimentary  rocks  of  the  Teton  uplift.  Separated  from  the  north- 
ern spurs  of  that  range  by  the  southern  extension  of  the  great  rhyolite 
plateaus  of  the  Park  which  so  effectively  conceal  all  the  earlier  rocks,  this 
small  area,  which  recent  denudation  has  again  exposed  to  view,  presents 
clear  evidence  of  the  same  sequence  of  events  S(i  clearh'  outlined  in  the 
range  itself 

The  hills  consist  of  a  group  of  pointed  eminences,  with  gentle  eastern 
slope  and  steep  western  declivities.  The  surface,  formerly  heavily  wooded, 
is  now  densely  covered  with  a  shrubby  gi'owth  of  black  birch,  concealing 
the  fallen  timber  that  everywhere  strews  the  ground. 

North  of  Falls  River,  whose  beautiful  Rainbow  and  Terrace  falls  are 
near  by,  the  hills  consist  of  dacite-porphyry,  forming  the  two  main  sununits. 
This  rock  is  light  gray  and  compact,  with  phenocrysts  of  feldspar  and  quartz, 
and  small  biotite  plates.  It  is  a  holocrystalline,  intrusive  body,  resembling 
the  rock  of  Bunsen  Peak  in  composition  and  structure,  but  more  distinctly 


BIRCH  HILLS. 


163 


])(>rj)liyritic,  tlio  i)henocrysts  being  larger  and  fewer.  They  are:  Oligoclase 
in  line  idioniorpliic  crystals,  with  marked  zonal  structure  and  little  ])olysyn- 
thetic  twinning,  sometimes  suggesting  ortlioclase;  biotite,  in  thick  idicmior- 
phic  crystals,  with  munerous  magnetite  inclusions;  and  corroded  quartz, 
with  glass  inclusions.  The  groundmass  is  microgranular  with  idiomorphic 
quartzes,  the  average  grain  being  about  0.02  mm.  in  diameter.  It  consists 
of  quartz  and  feldspar,  with  small  amounts  of  magnetite  and  biotite.  Apatite 
occurs  iu  comparatively  large  colorless  crystals,  nuich  cracked.  Zircon  is 
present  in  minute  prismatic  crystals.  The  chemical  composition  of  the  rock 
is  shown  in  the  following  analysis,  and  is  nearly  identical  with  that  of  the 
Bunsen  Peak  rock: 

Analysis  of  daciie-porphyry  of  the  Birch  Mills. 

[J.  E.  Whitfield,  Analyst.] 


Constitaent, 

Per  cent. 

SiOj 

70.24 

Trace. 

17.36 

1.38 

.79 

None. 

.53 

2.74 

3.69 

2.65 

None. 

Trace. 

Trace. 

.71 

TiOj 

Al^Oa 

Fe^Oa 

FeO 

MnO 

MgO .   . 

CaO  '. 

Na-O 

K.O 

Li  0 

P2O5 

SO, 

H,0 

Total 

100.09 

Eastward  this  rock  jjasses  beneath  the  rhyolites,  which  reach  almost 
to  the  summit  of  the  hills.  On  the  westward  slopes  steeply  upturned 
limestones,  somewhat  altered,  dip  toward  the  igneous  rock.  The  foot  slopes 
show  a  remnant  of  the  basic  breccias  covering  the  eroded  limestones  and 
porphyry,  and  covered  in  turn  by  the  ubiquitous  rhyolite. 

The  west  spur  of  the  northern  hill  is  formed  of  altered  limestones, 
whose  beds  strike  S.  40°  E.,  and  dip  70°  NE.,  toward  the  dacite-porphyr-s'. 
The  limestone  is  dense,  gray,  mottled  with  yellow,  and  underlies  thinly 


164  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

liedded  glaucouitic  limestones  whose  litliological  character  and  sequence 
place  them  in  the  Flathead  formation  of  the  Cambi'ian. 

Similar  rocks  are  exposed  in  the  bed  and  Avails  of  Falls  River  belov?^ 
the  Rainbov\^  Falls,  where  they  are  covered  by  a  light-colored  andesitic  tuff 
or  breccia,  generally  fine  grained  and  much  decomposed.  This  breccia 
forms  low  rounded  hummocks  at  the  base  of  the  hills,  and  is  not  yet  cut 
throup-h  bv  the  river,  whose  bed  it  forms  for  a  mile  above  the  meadows. 
The  exposure  in  the  river  bank  shows  rude  bedding,  with  northwest  dip. 

South  of  Falls  River  the  hills  are  continued  in  an  irregularly  accidented 
area.  The  rhyolite  plateau  terminates  in  a  wall  several  hundred  feet  high, 
a  deep  but  narrow  depression  separating  the  bluff  from  the  sedimentary 
ridge  to  the  west. 

These  hills  south  of  the  river  jjresent  exposiu-es  of  the  Carboniferous 
and  Triassic  beds,  forming  jjarallel  ridges  with  benched  slope  and  trending 
N.  70°  E.,  the  rocks  dipping  30"  N.  The  red,  fissile  Teton  sandstones  are 
well  exposed  in  the  lower  slopes,  weathering  into  a  reddish  soil  not  easily 
distinguished  from  that  of  the  red  patches  of  the  Quadrant  formation. 

These  red  sandstones  are  here  underlain  by  the  cherty  horizon  of  the 
Teton,  resting  upon  the  Quadrant  quartzites.  The  chert  occurs  in  charac- 
teristic rolls,  rods,  and  nodular  masses,  having  a  chalky  surface,  and  grading 
at  times  into  the  inclosing  arenaceous  rock.  The  Quadrant  quartzites  cor- 
respond closely  in  character  to  the  formation  as  developed  in  the  Gallatin, 
consisting  of  white  granular  quartzite  and  interbedded  limestones  that  are 
often  good  marbles. 

West  of  the  sedimentary  area  just  noted  there  is  an  exposure  of 
hornblende-andesite-porphyry.  The  rock  is  clearly  intrusive  and  cuts 
through  the  Carboniferous  limestones. 

The  Birch  Hills,  by  reason  of  the  compact  character  of  their  rocks, 
present  excellent  evidences  of  former  glaciation  of  the  region.  The  rocks 
occur  in  rounded  ice-worn  hummocks,  covered  with  glacial  scorings  and 
groovings  with  general  east-west  trend.  In  general  the  eastern  and 
northern  slopes  are  gentle,  while  steep  cliffs  bound  the  hills  to  the  west 
and  south. 


CHAPTER    V. 

descriptivp:  geology  of  huckleberry  mountain 
and  big  game  ridge. 


By  Arnold  Hague. 


GEISTERAL   FEATURES. 

The  country  described  iit  this  chapter  embraces  a  mountainous  area 
iiTegular  in  outhne  and  of  great  diversity  of  form.  It  consists  mainly  of 
a  series  of  ridges,  trending  northwesterly  and  southeasterly,  composed  for 
the  most  part  of  Mesozoic  rocks.  Older  sedimentary  rocks  are  well  exposed 
in  a  number  of  localities,  as  Avell  as  areas  of  coarse  breccia  and  broad 
fields  of  rhyolite,  but  the  region  is  essentially  one  formed  of  rocks  of 
Cretaceous  age. 

The  southern  line  of  the  area  descriljed  here  is  sharply  defined  by  the 
forty-fourth  parallel  of  latitude,  coinciding  with  the  southern  boundary  of 
the  Yellowstone  Park  forest  reservation.^  The  broad  valley  of  the  Snake 
separates  it  from  the  mountains  and  uplifted  sedimentary  rocks  of  the  Teton 
Range  lying  on  the  west  side  of  the  river.  On  the  northwest  and  north  the 
rhyolites  of  the  Park  Plateau,  reaching  their  southern  limit,  rest  directly 
against  the  upturned  edges  of  the  sedimentary  beds.  In  much  the  same  way 
the  western  border  of  andesitic  breccias  of  Two  Ocean  Plateau  sharply 
delimit  this  area  of  sedimentary  rocks  from  the  unbroken  mass  of  basic 
lavas  which  stretch  far  away  eastward  in  broad  plateaus  and  seiTated 
ridges.  In  striking  contrast  to  these  areas  of  breccias  and  rhyolites  that 
surround  it,  this  region  stands  out  strongly  marked  by  its  physical  features. 
In  a  certain  way  this  group  of  sedimentary  ridges  rises  as  an  island,  or 
rather  as  a  projecting-  promontory,  into  a  vast  sea  of  lavas.     The  irregular 

'  See  map  of  Yellowstone  National  Park  aocompanyiug  Part  I,  aud  Geologic  Atlas  U.  S.,  folio  30, 189(). 

165 


166  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

outline  is  in  great  part  due  to  the  sinuous  border  of  accumulated  lavas  that 
abut  against  the  steep  slopes  of  uplifted  strata.  Across  its  broadest  expan- 
sion, from  Snake  River  to  Two  Ocean  Plateau,  it  measures  about  20  miles. 
In  length  it  measures  nearly  22  miles,  stretching  northward  with  decreasing 
breadth  across  the  forest  reservation,  gradually  dying  out  in  a  narrow  ridge 
projecting  into  the  rhyolite  body  which  skirts  the  west  shoi'e  of  the  south 
arm  of  Yellowstone  Lake. 

All  of  the  ridges  and  mountain  masses  which  make  up  this  region 
are  clearly  defined  by  salient  topographic  features,  delimited  by  deeply 
eroded  valleys,  and  yet  they  are  all  so  knit  together  by  outlying  spurs  and 
elevated  passes  as  to  present  a  single  mountain  grouj),  with  a  somewhat 
complex  topographic  structure  and  an  intricate  drainage  system.  The 
principal  physical  features  are  Big  Game  Ridge  and  its  extension  north- 
ward, Chicken  Ridge;  Piiiyon  Peak  and  Bobcat  Ridge;  HucklebeiTy 
Mountain  and  Wildcat  Peak.  Several  of  the  high  mountains  of  the  Park 
country  are  found  here,  a  number  of  them  attaining  elevations  of  over 
9,500  feet,  but  only  one,  Mount  Hancock,  the  culminating  point  of  Big 
Game  Ridge,  reaches  an  altitude  of  over  10,000  feet  above  sea  level. 
With  the  exception  of  a  narrow  strip  of  country  pouring  its  waters  into 
Yellowstone  Lake,  this  entii-e  region  is  drained  by  Snake  River  or  some  of 
its  many  tributary  streams.  The  main  branch  of  Snake  River  takes  its  rise 
along  the  west  slopes  of  Two  Ocean  Plateau,  flows  northerly  around  the 
east  base  of  Mount  Hancock,  and  thence,  with  a  sharp  curve  around  the  end 
of  Big  Game  Ridge,  runs  southerly  at  the  west  base  of  the  same  mountain. 
With  a  gentle  sweeping  curve  it  encircles  the  northern  end  of  Huckleberry 
Mountain  and  enters  the  broad,  open  plain  lying  west  of  this  mountainous 
region.  Continuing  its  course  southward,  it  crosses  the  forest  reserva- 
tion, and  soon  after  widens  out  into  Jackson  Lake,  a  short  distance  south 
of  the  limit  of  the  map.  With  this  circuitous  course,  as  thus  defined.  Snake 
River  nearly  surrounds  this  group  of  mountains,  and  on  leaving  the  forest 
reservation  has  become  a  wide,  deep  stream.  Across  the  broadest  expanse 
of  these  mountains  there  runs,  in  an  approximately  east-west  line,  a  well- 
defined  watershed  from  Snake  River  to  Two  Ocean  Plateau.  North  of 
this  divide  such  fine  streams  as  Coulter,  Wolverine,  and  Fox  creeks  pour 
large  volumes  of  water  into  the  main  Snake.  Several  mountain  torrents, 
notably  Lizard,   Gravel,   and    Mink    creeks,  flow  southward    into   Pacific 


THYSIOAL  FEATUHKS  OF  nUCKLEBERRY  MOUNTAIN.  167 

Creek,  which  tinally  adds  its  waters  to  those  of  the  Snake  soon  after  the 
latter  stream  crosses  tlie  soutliern  boundary  of  the  area  mapped. 

The  physical  features  of  the  country  present  strikinj^ly  varied  outlines 
of  mountain,  ridfje,  valley,  and  upland,  with  abrupt  changes  in  coniiguration. 
Constantly  changing-  rock  formations,  with  accompanying  modifications  of 
topogi'a{)hic  forms,  make  the  region  singularly  pictui'esque,  and  the  alterna- 
tion of  gently  undulating  and  roughly  accidented  areas  causes  the  region 
to  stand  out  in  sharidy  deiined  contrast  to  the  more  monotonous  Park 
Plateau. 

i\Iuch  of  the  country,  especially  the  more  elevated  portions,  are  timber- 
less,  but  large  areas  of  mountain  slope  present  a  diversified  park-like 
appearance,  covered  with  a  vigorous  growth  of  coniferoiTs  forest.  Faulting- 
and  folding  of  strata,  with  frequent  changes  in  the  inclination  of  beds,  have 
produced  conditions  favorable  to  the  flow  of  springs,  the  many  mountain 
torrents  making  the  region  a  highly  favored  one  in  its  water  supply. 

The  region  is  well  adapted  to  the  haunts  of  Avild  animals,  and  the 
dominant  ridge  of  the  country,  characteristically  named  Big  Game  Ridge, 
in  former  years  furnished  abundant  sport  for  the  hunter  in  search  of  bear, 
elk,  deer,  and  mountain  lion. 

Unlike  the  areas  of  sedimentary  beds  which  make  up  the  Gallatin 
Range  and  form  the  slopes  of  the  Teton  or  Snowy  ranges,  the  sedimentary 
rocks  of  this  region  do  not  rest  directly  upon  any  exposed  bod  v  of  Archean 
rocks,  nor  do  they  dip  away  in  any  one  direction  from  a  central  mass. 
Within  this  region  no  x\rchean  rocks  are  known.  Southward,  in  the  Wind 
River  Range,  the  Archean  presents  a  bold  unbroken  mass  of  pre-Cambrian 
rocks,  but  its  geological  relations  with  the  uplifted  sediments  of  this  region 
can  not  be  determined,  owing  to  the  accumulated  volcanic  material,  which 
conceals  everything  beneath  it  in  the  intervening  country.  In  much  the 
same  manner  the  breccias  of  Two  Ocean  Plateau  and  the  rhyolites  of  the 
Park  Plateau  prevent  any  precise  interpretation  of  the  structural  relations 
of  this  region  with  the  country  to  the  north  and  east. 

It  is  evident  that  the  powerful  forces  which  uplifted  this  mountain  mass 
acted  from  several  different  centers  and  produced  a  somewhat  intricate 
structure.  The  uplifting  of  the  mass  was  accompanied  by  profound  fault- 
ing and  folding,  and  in  places  by  marked  compression  of  strata.  Subse- 
quent orographic  movement  produced  secondary  faulting,  adding  much .  in 


168  GEOLOGY  OF  THE  YELLOWSTONE  NATIOlsTAL  PARK. 

certain  localities  to  the  difficulties  of  determining  structure.  The  later 
intrusion  of  igneous  rocks  tended  in  some  places  to  break  \\\i  and  confuse 
the  position  of  beds,  but  only  in  limited  areas  is  such  action  especially 
noticeable,  and  it  may  be  said  to  have  affected  the  larger  mountain  blocks 
singularly  little  as  regards  the  disturbance  of  beds. 

Sandstones  of  the  Montana  and  Laramie  formations  constitute  the  moi*e 
elevated  portions  of  the  ridges.  Both  formations  are  conformable,  and 
throughout  their  entire  development,  from  base  to  summit,  the  prevailing- 
beds  consist  of  a  coarse  yellowish-brown  sandstone,  of  varying  degrees  of 
purity.  In  the  absence  of  a  characteristic  fauna  discrimination  between 
the  two  formations  is  very  difficult,  and  in  most  instances  impossible  with- 
out much  detailed  work,  with  results  not  commensurate  to  the  labor. 

Fort  Pierre  beds,  which  are  mainlj^  arenaceous,  pass  down  into  nearly 
similar  sandy  deposits  of  the  Colorado.  The  fauna  which  characterizes 
these  lower  beds  is  one  possessing  a  wide  vertical  range  throughout  the 
Cretaceous  sandstones,  and  the  line  of  demarcation  between  the  Montana 
and  Colorado  is  not  always  easy  to  draw.  It  is  possible  that  beds  provi- 
sionally placed  in  the  Montana  may  upon  further  investigation  be  found  to 
belong  to  the  Colorado,  the  assignment  being  based  upon  their  faunal 
relations  rather  than  upon  their  lithological  habit. 

REGION  OF  WILDCAT  PEAK  AND  HUCKLEBERRY  MOITNTAHST. 

Snake  River  sharply  defines  this  group  of  mountains  on  the  west  and 
north.  Above  the  broad  valley  of  the  Snake  the  niountains  rise  abruptly 
over  2,500  feet  in  long  rugged  ridges  whose  outlines  are  more  or  less 
obscured  by  dense  forests.  Northward,  along  the  gorge  of  Snake  River, 
the  mountain  slopes  are  precipitous  and  in  places  rise  like  canyon  walls 
above  the  stream. 

Coulter  Creek,  named  in  honor  of  the  distinguished  botanist.  Prof. 
John  M.  Coulter,  may  be  taken  as  the  eastern  boundary  of  these  moun- 
tains. It  drains,  by  numerous  tributaries,  nearly  the  entire  eastern  slope,  and 
pours  a  large  volume  of  water  into  the  main  stream,  being  the  first  impor- 
tant affluent  above  the  gorge  of  the  river.  The  summit  of  the  mountains  at 
their  northern  end,  with  an  average  elevation  of  8,700  feet,  presents  a  broken, 
gently  accidented  country,  easy  to  traverse  and  singularly  attractive  from 
its  park-like  character.     All  the  dominant  peaks  attain  nearly  the  same 


WILDCAT  PEAK.  109 

elevation,  are  fiat-topped,  and  easily  aci-essible.  Numerous  groups  of  conif- 
erous trees,  broad  areas  of  grassy  upland,  and  an  abundance  of  water  add 
great  charm  to  the  region.  South  of  Wildcat  Peak  the  country  falls  away 
in  long  monotonous  ridges,  with  narrow  inter\'eiung  valleys,  uniform  in  out- 
line and  dreary  in  aspect.  Structurally  this  uplifted  mass,  in  its  simplest 
form,  presents  a  synclinal  fold,  whose  axis,  with  a  broad  sweeping  curve, 
strikes  obliquely  across  the  mountains  northwest  to  southeast.  This  struc- 
ture is  accompanied  by  local  crumpling  and  folding  of  beds.  Apparently 
the  force  uplifting  the  beds  upon  the  southern  side  of  the  fold  came  from 
the  direction  of  the  Teton  Range.  Wherever  observed  these  beds  dip 
persistently  into  the  mountains  and  away  from  the  Archean  mass  which 
forms  so  broad  and  continuous  a  body  to  the  southwest.  Owing  to  the 
crumbling  nature  of  the  beds  and  the  amount  of  soil,  good  rock  exposures 
are  rarely  seen.  Along-  the  banks  of  Lizard  Creek  and  the  adjoining- 
valleys  to  the  east  and  west  the  beds  lie  inclined  from  20°  to  30°  NE.  The 
axis  of  the  syncline  trends  across  the  southern  and  western  slopes  of  Wild- 
cat Peak,  and  is  lost  beneath  the  rhyolite  forming  the  steep  slopes  toward 
Snake  River. 

Wildcat  Peak. — At  tlic  basc  of  Wildcat  Peak,  near  the  head  of  Lizard 
Creek,  the  beds  dip  slightly  to  the  northeast,  but  those  forming  the  summit 
of  the  peak  belong  to  the  opposite  side  of  the  syncline  and  are  highly 
inclined,  many  of  them  standing  on  edge.  Here  they  trend  diagonally 
across  the  ridge,  with  a  dip  varying  from  65°  to  70°.  The  strata  are  thinly 
bedded  sandstones,  presenting-  long  rows  of  slab-like  exposures.  These  are 
underlain  by  black  arenaceous  shales,  in  turn  followed  by  other  thin  layers 
of  sandstone.  The  beds  striking  across  the  ridge  give  rise  to  narrow  lateral 
spurs,  with  deeply  eroded  ravines  between  them.  Along  the  summit  of  the 
ridge  the  same  beds  may  be  traced  eastward  with  apparently  the  same  dip 
and  strike.  In  the  open  park-like  country  northwest  of  Wildcat  Peak  and 
west  of  Huckleberry  Mountain  the  beds  show  a  southerly  dijD,  indicating 
the  north  side  of  the  syncline.  The  beds  found  on  both  sides  of  the  axis 
of  this  fold  have  been  referred  to  the  Montana  formation.  It  is  possible 
that  they  include  a  series  of  beds  which  should  be  assigned  to  the  Colo- 
rado, but,  owing  to  the  present  state  of  knowledge  and  the  very  limited 
number  of  organic  forms  as  yet  obtained  from  this  region,  it  has  been 
found  impossible  to  draw  any  line  of  demarcation  between  the  two  periods 


170  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  the  Cretaceous.  All  the  sediments  are  more  or  less  impure  sandstones, 
and  even  those  cliaracterized  by  argillaceous  deposits  are  usually  sandy. 
While  the  org-anic  forms  found  here  niay  be  such  as  occur  elsewliere  in  the 
Colorado  shales,  they  are  also  forms  tliat  extend  upward  into  the  sandstones 
of  the  Montana.  These  arenaceous  shales  are  well  developed  in  the  valley 
of  Lizard  Creek,  and  along  the  east  side  of  the  stream  are  exposed  in  a 
number  of  localities  above  the  stream  bed.  From  them  have  been  obtained 
Ostrea,  Anomia,  Inoceraraus,  and  the  widely  distributed  middle  Cretaceous 
species,  Gardium  iMuperculiun. 

Beds  similar  in  lithological  habit  are  exposed  in  the  valley  to  the  west- 
ward, which  in  its  topographic  outline  closely  resembles  Lizard  Creek,  and 
still  farther  westward  these  rusty  sandstones  crop  out  from  beneath  thin 
cappings  of  rhyolite  at  a  number  of  localities  on  both  sides  of  the  Snake 
River  trail.  One  such  exposure  is  seen  along  the  trail  not  far  from  where  it 
crosses  the  summit  of  the  spur  which  extends  westward  to  Snake  River. 
On  the  east  side  of  the  river,  opposite  the  mouth  of  Berr}^  Creek,  a  small 
exposiire  of  sandstone  and  shale  occurs,  striking  nearly  due  east  and  west 
and  dipping  north. 

Owing  to  the  limited  area  exposed  and  the  fact  that  the  surrounding- 
country  is  mainly  covered  by  drift  the  outcrop  is  not  indicated  on  the 
map.  According  to  Prof  J.  P.  Iddings,  this  sandstone  carries  a  seam  of  coal 
4  inches  in  thickness.  Northward,  and  on  the  extreme  western  spur  of  the 
ridge,  the  sandstones  and  shales  are  exposed,  extending  up  the  hill  slope  for 
several  hundred  feet.  Here  they  strike  northeast  and  southwest,  with  a 
dip  of  25"  NW.  It  is  possible  these  beds  belong  to  the  Colorado  fox-ma- 
tion,  but  in  the  absence  of  all  organic  remains  they  have  been  placed  in  the 
^Montana,  together  with  other  beds  of  similar  lithological  character  found 
in  tliis  region. 

Huckleberry  Mountain. — Tlic  ccutral  mass  of  tlus  gToup  of  mouutaius  has 
been  designated  Huckleberry  Mountain.  Its  summit  is  formed  of  a  broad 
sheet  of  rhyolite,  slightly  inclined  toward  the  south.  On  nearly  all  sides 
this  rhyolite  capping  rises  above  the  underlying  rocks  as  an  abrupt  Avail, 
Avhich  along  the  east  side  forms  an  escarpment  over  100  feet  in  height. 
This  east  wall  limits  the  rhyolite  in  this  direction,  and  the  entire  eastern 
slope  of  the  mountain,  down  to  Coulter  Creek,  exposes  only  strata  of  the 
Montana  formation.     The  beds  dip  at  low  angles  to  the  southeast.     Beneath 


HUCKLEBERRY  MOUNTAIN.  171 

tlie  rliyolite  of  the  summit  the  Montana  beds  present  a  very  uneven  surface, 
and  at  one  point  tlie  sandstones  ])roject  tln'ou^^li  tlie  capping'  of  lava,  which 
elsewhere  forms  the  top  of  the  mountain.  On  both  the  east  and  west  slopes 
of  lluekleberry  Mountain  the  underlying  strata  ])resent  many  of  the  same 
general  features,  being  fissile,  friable  sandstone,  crumbling  easily,  and  in 
places  showing  signs  of  cross  bedding  and  other  evidences  of  shallow-water 
deposition.  On  the  west  side,  where  the  sandstones  are  exposed  by  erosion 
of  the  rliyolite,  the  beds  have  yielded  Card'mm  paHperciiliim,  and  on  the  east 
side,  just  below  the  base  of  the  rliyolite,  the  same  species  has  been  obtained 
from  nearly  similar  rock.  Again,  near  the  east  end  of  the  long  spur 
making  out  toward  Coulter  Creek,  in  fissile  sandstone,  inclined  10°  S., 
there  were  found  the  same  Cardium,  associated  with  Ostrea  anomioides. 

North  of  HucklebeiTy  Mountain  the  country  suddenly  falls  away 
several  hundred  feet  to  a  narrow  saddle,  where  the  Montana  shales  are  ag-ain 
well  shown.  Beyond  this  saddle  the  country  again  rises  in  a  prominent 
point,  which,  for  want  of  any  distinctive  appellation,  may  be  designated  as 
North  Huckleberry  Mountain.  In  elevation  it  falls  but  little  below  the 
more  southern  point,  and  commands  to  the  north  a  still  more  comprehensive 
view.  Geologically  the  two  points  possess  much  in  common.  A  sheet  of 
rhyolite,  resting  upon  the  Montana  sandstone,  forms  the  top  of  the  table,  as 
already  described  for  Huckleberry  Mountain.  Probably  at  one  time  the 
two  points  wei'e  connected  by  a  continuous  sheet  of  rhyolite,  erosion  having 
since  worn  away  the  rock  upon  the  saddle.  In  the  case  of  North  Huckle- 
berry Mountain  the  rhyolite  escarpment  faces  northward,  and  the  prominent 
wall  of  Montana  sandstone  stretches  far  away  to  the  eastward  till  buried 
beneath  the  ovitlying  masses  of  late  basic  breccia. 

The  fissile  sandstones  of  the  Montana  beds  are  well  shown  all  along  the 
northern  slopes  of  the  mountain  and  in  the  valley  of  the  stream  tributary 
to  Coulter  Creek.  Northward,  the  Montana  sandstone  still  forms  the 
summit  of  the  main  ridge  and  eastern  slopes,  till,  near  the  northern  end  of 
the  mountain,  the  beds  become  decidedly  argillaceous,  with  sandstone  occur- 
ring as  intercalated  layers.  Although  no  evidence  of  a  fauna  was  obtained, 
the  beds,  upon  their  lithological  habit  in  distinction  to  the  arenaceous  beds 
above,  have  been  assigned  to  the  Colorado  formation.  Their  continuity 
westward  is  obscured  by  overlying  rhyolite.  Montana  sandstones  occur  as 
the  underlying  rocks  along  the  entire  western  slope  of  this  mountain  mass, 


172     GBOLOGl  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

and  extend  from  the  open  plain  of  Snake  River  Valley  to  the  summit  of  the 
ridge.  At  one  locality  just  south  of  the  Park  boundary  Cretaceous  clays 
are  exposed  in  a  precipitous  bluff  at  the  river,  but  the  slopes  of  the  hills 
are  for  the  most  part  obscured  by  alluvial  material,  followed  higher  up 
by  extensive  deposits  of  glacial  drift  and  broad  areas  of  rhyolite,  the  latter 
in  places  extending  from  the  summit  to  the  plain.  An  overlying  sandy 
soil  nearlv  everywhere  mantles  the  mountain  side,  and  large  fox'est  areas 
conceal  the  structure  of  beds,  rendering  it  most  difficult  to  follow  the  con- 
tinuity of  strata.  Observed  dips  and  strikes  indicate  that  in  general  the 
sandstones  lie  inclined  eastward,  toward  the  mountain  mass,  but  with  many 
local  displacements. 

Rhyolite. — By  reference  to  the  map  it  will  be  seen  that  the  rhyolite  is 
represented  as  forming  a  continuous  body  from  the  extreme  northern  end 
of  the  mountain  south  to  the  forty-fourth  parallel  of  latitu.de.  This  rhyolite 
is  very  irregular  in  outline  and  represents  a  comparatively  thin  flow  of  lava. 
Over  a  large  part  of  the  area  covered  by  rhyolite  it  is  doubtful  if  the  lava 
sheet  is  more  than  100  feet  in  thickness.  In  places  it  has  been  entirely 
removed  by  erosion,  leaving  isolated  patches  of  sandstone  exposed  upon 
the  surface.  In  two  localities  it  caps  the  westward  spurs  from  the  summit 
to  Snake  River,  and  at  other  points  lies  high  up  on  the  mountain  sides.  It 
caps  the  sandstone  on  the  long  ridges  trending  southward,  and  presents  a 
somewhat  striking  appearance  with  its  long  monotonous  flows,  scarcely  100 
feet  in  thickness,  resting  upon  the  deeply  eroded  arenaceous  strata.  These 
long  flows  stretch  southward  nearly  to  Jackson  Lake. 

This  rhyolite  body  possesses  a  fairly  uniform  appearance  from  one  end 
to  the  other;  that  is  to  say,  it  does  not  vary  throughout  its  mass  more  than 
many  areas  of  equal  extent  on  the  Park  Plateau;  indeed,  it  closely  resembles 
the  rhyolite  of  the  Park.  It  is  in  general  purplish  gray  in  color  and  lithoidal 
in  texture.  In  places  it  is  fissile,  and  upon  Huckleberry  Mountain,  and  in 
several  other  localities  along  the  summit,  it  occurs  in  horizontal  beds  with 
jointing  planes.  On  North  Hucklebeny  Mountain  it  is  thinly  bedded  and 
fissile,  the  debris  slopes  being  made  up  of  irregular  fragments  of  lithoidal 
rock. 

Dacite. — Near  the  junction  of  the  Cretaceous  rocks  with  the  rhyolite,  due 
west  of  Huckleberry  Mountain,  occur  two  or  three  exposures  of  igneous 
rock,  that  rise  in  low  obscure  mounds  above  the  general  level  of  the  sand- 


SNAKK  IIIVER  GORGE.  173 

stone.  In  outline  these  exposures  are  strikiugly  different  from  the  sand- 
stone, fuid  in  tht'ir  mode  of  weathering  stand  out  in  strong  contrast  with 
the  surrounding  rliyoUte.  An  examination  shows  that  these  rocks  are  to  be 
chissed  as  dacite.  In  composition  the}'  are  more  basic  than  the  rhyoHtes, 
and  carry  a  larger  proportion  of  })lagioclase,  and,  in  distinction  from  the 
rhyolites  of  the  region,  hold  a  considerable  amount  of  biotite.  Apparently 
they  are  older  than  the  rhyolite  and  are  exposed  by  the  erosion  of  the  latter 
rock.  Petrographically  they  are  closely  related  to  a  dacite  occurring  in  a 
number  of  exposures  on  the  west  side  of  Snake  River  Valley,  and  their 
interest  lies  in  the  fact  that  they  are  among  the  few  instances  known  in  the 
Park  of  rocks  with  a  dacitic  facies  related  to  rhyolites. 

REGION  OF  SNAKE  RIVER  GORGE. 

From  Lewis  River  to  the  mouth  of  Coulter  Creek  the  course  of  Snake 
River  makes  an  irregular  curve  of  nearly  180°,  closely  encircling  the 
northern  end  of  the  Wildcat  Peak  and  Huckleberry  Mountain  mass,  the 
mouth  of  Coulter  Creek  lying  7J  miles  due  east  of  Lewis  River.  Snake 
River  runs  through  a  deeply  eroded  gorge,  which  for  several  miles  above 
Lewis  River  sharply  defines  the  rhyolite  flows  of  the  Sheridan  volcano  on 
the  north  side  from  the  uplifted  sedimentary  rocks  on  the  south.  Against 
the  abrupt  wall  of  Paleozoic  rocks  the  rhyolites  were  piled  up  to  a  great 
height,  and  it  is  along  this  contact  that  the  river  has  cut  its  picturesque 
gorge.  On  the  north  side  the  rhyolites  stand  out  in  a  precipitous  wall, 
nearly  400  feet  above  the  river,  and  thence  rise  gradually  toward  the  centi-al 
portion  of  Mount  Sheridan.  On  the  south  side  a  massive  wall  of  limestone 
rises  1,000  feet  to  the  summit  of  the  mountain.  The  beds  are  highly 
crystalline,  light  in  color,  and  belong  to  the  Madison  limestone. 

It  is  possible  that  older  beds,  represented  by  Three  Forks  and  Jefferson 
limestones,  are  exposed  in  the  gorge  along  the  base  of  the  mountain,  but 
the  mantle  of  drift  is  so  heavy  and  the  timber  so  dense  that  they  have 
nowhere  been  recognized. 

Above  the  Madison  limestone  come  the  brilliant  red  sandstones  and 
shales  of  the  Teton  formation,  standing  out  conspicuously  in  contrast  with 
white  and  blue  limestone.  Along  the  summit  of  the  mountain  the  Quad- 
rant quartzite  has  nowhere  been  recognized.      Arenaceous  limestone  lies 


174  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

directly  beneath  the  Teton  beds,  but  nothing  similar  to  the  compact  siliceous 
deposits  which  characterize  the  Quadrant  quartzites  iu  the  Gallatin  Range 
has  been  observed. 

Overlying  the  Teton  beds  come  the  drab  limestone,  marl,  and  fine 
sandstone  which  mark  the  Ellis  formation,  everywhere  defined  by  Jurassic 
fauna.  Fine-grained  sandstones  which  form  the  uppermost  beds  of  the 
Ellis  formation  pass  gradually  into  a  coarser  and  more  compact  series 
of  sandstones,  which  here  represent  the  Dakota  beds.  These  in  turn  are 
followed  by  impure  sandstones  and  black  shales  of  the  Colorado  fornaa- 
tion,  and  these  again  b}^  the  Montana.  The  latter  have  ah-eady  been  referred 
to  in  describing  the  geological  features  north  of  Huckleberry  Mountain. 
This  entire  mass  of  uplifted  sediments  dips  to  the  south,  forming  a  part  of 
the  general  syncline  which  constitutes  the  Wildcat  Peak  and  Huckleberry 
IVIountain  orographic  block.  About  5  miles  east  of  LeAvis  River  the  phys- 
ical features  of  the  canyon  wall  change.  The  Madison  limestone,  dipping 
eastward,  dies  out,  and  the  Mesozoic  strata,  which  to  the  west  are  seen  only 
hifdi  up  on  the  cliffs,  turn  and  pitch  down  the  mountain  slope  toward  the 
river.  The  Mesozoic  strata  are  much  faulted  and  crumpled,  and  lie  inclined 
at  varying  angles.  Overlj'ing  the  Madison  limestone  the  Teton  red  beds 
incline  to  the  southeast,  but  the  dip  soon  changes,  and  the  beds  which  make 
up  the  long  ridge  stretching  down  to  the  river  dip  for  the  most  part  to  the 
southwest. 

Both  the  Teton  and  Ellis  formations  are  exposed  along  the  south  side 
of  the  river,  but  neither  the  Dakota  nor  Colorado  have  been  recognized 
along  the  river  bank.  Good  exposures  are  few.  The  Dakota  conglomerate 
is  not  characteristically  developed,  and  the  slopes  for  200  feet  above  the 
river  are  largely  covered  by  glacial  drift.  On  the  ridge  south  of  the  river 
and  west  of  Coulter  Peak,  where  the  Ellis  beds  are  well  exposed,  dipping 
at  a  low  angle  to  the  southwest,  the  drab  limestone  has  furnished  Ostrea 
sfrigilecda,  Camptonectes,  and  Bhijnchonella  myrma.  Several  hundred  feet 
higher  up  the  ridge,  in  the  arenaceous  limestone  passing  into  sandstone,  the 
same  species  were  obtained,  together  Avith  R.  gnathophora,  and  at  still 
another  locality  on  the  ridge  the  beds  yielded  Gryphcea  planoconvexa.  As 
regards  the  relative  position  of  the  horizons  furnishing  these  species  nothing 
definite  can  be  stated.  Still  higher  up  the  ridge  the  coarse  sandstones 
assigned  to  the  Dakota  formation  ai-e  well  exposed,  and  above  the  Dakota 


RED  CREEK  SANDSTONE.  175 

nunuTous  drainatjo  channels,  triltutarics  of  the  western  affluent  of  Coulter 
Creek,  aH'orcl  i^ootl  exjjosures  of  the  higher  Cretaceous  formations. 

KKOION   IJKTWKKN   UKI)   AND   BASIN   CREEKS. 

East  of  Red  Creek  the  gorge  of  the  river  narrows,  and  the  clear 
shallow  water  presents  a  striking  ap})earance,  flowing  for  more  than  half 
a  mile  over  a  smooth,  polished  floor  of  Teton  red  beds,  with  the  highly 
colored  sandstone  forming  the  brilliant  banks  on  both  sides  of  the  stream. 
On  the  north  and  east  side  of  Snake  River,  between  Red  and  Basin  creeks, 
there  is  a  mountain  area  consisting  mainly  of  Mesozoic  rocks.  It  extends 
back  from  the  river  about  5  miles,  and  across  its  broadest  expansion  meas- 
ures somewhat  less  than  4  miles.  Rhyolite  surrounds  it  on  all  sides,  except 
along  the  river  gorge,  effectually  isolating  it  from  adjoining  areas.  Geo- 
logicall}-  this  region  is  closely  related  to  the  Mesozoic  rocks  on  the  south 
side  of  the  river,  every  formation  being  represented,  from  the  Teton  to  the 
Montana,  inclusive. 

Red  Creek,  which  is  appropriately  named  from  the  red  rocks  found  on 
both  sides  of  the  stream,  marks  the  eastern  boundary  of  the  rhyolite  flow, 
stretching  southward  from  the  Sheridan  volcano.  Red  Creek  enters  Snake 
River  through  a  narrow  chasm  cut  in  the  sedimentary  rocks.  At  the 
mouth  of  the  creek  there  is  a  bluff  of  red  arenaceous  limestone,  similar  to 
the  Carboniferous  limestone  found  elsewhere  underlying  the  red  sandstone 
of  the  Teton  formation.  It  has  been  designated  on  the  map  as  the  Madi- 
son limestone,  but  it  may  belong  to  the  Quadrant  formation,  for  the  upper 
beds  are  nearly  pure  sandstone. 

Passing  up  Red  Creek  the  limestone  soon  disappears  and  is  overlain 
by  the  red  sandstone.  The  stream  for  nearly  its  entire  length  has  carved 
its  channel  in  these  beds,  which  are  here  exceptionally  well  exposed,  show- 
ing the  varying  character  of  the  sandstones  and  the  intercalated  red  clays 
and  marls.  The  formation  here  has  an  estimated  thickness  of  400  feet,  the 
beds  dipping  north  and  east.  Between  Red  Creek  and  Basin  Creek  the  beds 
are  pressed  into  a  syncline,  followed  by  a  sharp  anticline.  Overlying  the 
Teton  beds  of  Red  Creek  come  the  Ellis  and  Dakota  formations,  followed 
by  the  black  clays  and  arenaceous  shales  of  the  Colorado,  which  lie  in  the 
syncline,  the  latter  formation  being  characteristically  shown  in  a  depression 
between  two  ridges  of  less  easily  eroded  beds. 


176  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

To  the  east  of  this  depression  the  sandstones  assigned  to  the  Dakota 
formation  are  clearly  defined  along  the  west  side  of  the  prominent  ridge 
separating  Red  and  Basin  creeks.  They  pass  gradually,  without  any  sharp 
line  of  demarcation,  over  into  the  Ellis  beds,  which  form  the  summit  of 
the  ridge.  The  axis  of  the  anticline  lies  in  the  Ellis  limestone,  which  is 
here  nearly  200  feet  in  thickness,  and  is  characterized  by  a  small  but  well- 
defined  Jurassic  fauna.  Among  the  species  found  here  are  Gryphcea  calceola 
var.  nebrascensis,  Campfonecies  pertenuistriatus,  Gervillia,  Fseudomonotis  curta, 
ModioJa  suhimhricata,  Ammonites. 

At  the  east  base  of  the  ridge  and  on  the  opposite  side  of  the  anticline 
the  Dakota  sandstones  ag-ain  come  in,  dipping  eastward  until  finally  lost 
beneath  the  rhyolite  which  skirts  the  edge  of  the  upturned  sedimentary 
beds. 

East  of  Basin  Creek  the  valley  of  the  Snake  is  broad  and  open,  show- 
ing wide  alluvial  meadow  lands,  diversified  by  occasional  growths  of  pine. 
A  short  distance  below  the  mouth  of  Basin  Creek  the  river  flows  through  a 
narrow  chasm  before  it  enters  the  wider  valley  near  its  junction  with  Covilter 
Creek.  At  the  upper  entrance  of  this  chasm  the  river  cuts  through  a  ridge 
of  coarse  breccia,  showing  a  mural  face  nearly  300  feet  in  height.  This 
breccia  rests  upon  Montana  sandstones,  which  form  the  greater  part  of  the 
hills  on  the  west  side  of  the  river.  On  the  east  side  of  this  chasm,  about 
half  a  mile  above  the  junction  of  the  river  with  Coulter  Creek,  occur  two 
outcrops  of  coal,  exposed  just  above  the  river  bank.  These  seams  of  coal 
along  the  outcrops  measure  about  15  inches  in  thickness.  They  are  over- 
lain by  fine  conglomerate  and  underlain  by  black  arenaceous  clay.  These 
coals  are  more  or  less  impure  by  reason  of  thin  bands  of  carbonaceous 
clay.  The  beds  caiTying  the  coal  strike  N.  30°  W.  and  dip  from  15°  to 
20°  E.  The  bedded  sandstones  carrying  the  coal  seams  pass  under  the 
river,  but  are  not  exposed  on  the  o^iposite  side,  owing  to  the  accumulation 
of  glacial  drift.  Below  the  junction  of  C.oulter  Creek  with  the  Snake  the 
sandstones  dip  to  the  northeast,  away  from  the  river,  while,  as  already 
noted,  they  dip  to  the  southwest  on  the  opposite  side  of  the  stream. 

Notwithstanding  the  occurrence  of  coal  these  sandstones  are  regarded 
as  belonging  to  the  Montana  formation,  and  probably  to  the  iipper  part,  or 
the  Fox  Hill  terrane.     Owing  to  the  great  uniformity  in  the  sedimentation 


SNAKE  KIVEK  HOT  SPUINCS.  177 

of  these  beds  and  tin-  absence  of  orij^anic^  remains,  it  is  impossible  to  deter- 
mine with  precision  the  position  of  these  coals.  Unlike  the  Montana  sand- 
stone north  of  the  Park,  these  rocks  fre([ueTitly  carry  well-defined  coal  seams, 
alth(Hi<>;h  Vieds  of  economic  value  are  foiuid  mainly  in  the  Laramie.  This 
coal  is  probably  of  the  same  age  as  that  exposed  in  the  banks  of  the  Snake 
River  west  of  Wildcat  Peak. 

SNAKK   lilA'EU    HOT   SPllINGS. 

On  the  sonth  side  of  the  river,  below  the  mouth  of  Red  Creek,  occurs 
an  interesting-  group  of  hot  sj)rings,  more  than  half  hidden  by  dense 
tindier,  which  at  this  point  come.s  down  to  the  water's  edge.  A  low  cliff  of 
bine  cherty  limestone  is  exposed  along  the  bank,  beneath  which,  from  a 
line  of  springs,  there  issues  a  large  volume  of  warm  calcareous  waters. 
Near  by  is  a  long  bench  of  rhyolite,  rising  slightly  above  the  stream,  and 
the  only  one  observed  on  the  south  side  of  the  river.  The  thermal  waters 
are  probably  closely  related  to  this  body  of  rhyolite,  but  their  mineral 
constituents  are  derived  mainly  from  the  limestone.  These  springs  divide 
naturally  into  three  groups,  but  their  mode  of  occurrence  is  much  the 
same  and  they  are  similar  as  regards  the  mineral  composition  of  the 
deposits.  The  travertine  deposits  in  their  moimds,  basins,  and  terraces 
resemble  those  found  at  the  Mammoth  Hot  Springs.  They  were  visited  by 
the  writer  in  1886  and  again  in  1891;  they  presented  but  slight  changes 
after  this  interval  of  five  years.  The  most  picturesque  and  ])owerful  of  the 
springs  are  situated  farthest  up  the  river  and  are  built  out  over  the  stream 
upon  the  edge  of  an  old  meadow.  It  was  estimated  in  1886  that  the  volume 
of  water  running  from  these  springs  reached  50  gallons  a  minute.  This 
group  of  springs  is  shown  in  PI.  XXIV.  For  beauty  of  color  and  orna- 
mentation of  the  rim  they  are  unsurpassed  by  any  of  those  at  the  Mammoth 
Hot  Springs,  although  by  no  means  equal  to  them  in  magnitude  of  the 
deposits  or  in  volume  of  calcareous  water  poured  forth.  The  clear  water 
is  of  the  most  delicate  turquoise-blue  color,  and  the  basin  is  lined  with  a 
soft  white  travertine  of  extremely  fine  texture,  impalpable  to  the  touch. 
The  basins  which  surround  the  pool  are  tinted  with  orange,  brown,  and 
red  colors,  derived  from  the  hot-water  algse. 

Mr.   W.   H.   Weed  has  furnished   trom    his    notebook    the  following 

MON    XXXII,  PT.  II 12 


178  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

description  of  the  springs  lying  to  the  westward,  written  at  the  time  of  his 
visit  in  the  antunni  of  1891: 

One  sj^riug.  issuing  from  sandy  mire,  is  2  feet  in  diameter,  and  has  built  up  about 
tbe  orifice  a  deposit  of  white  calcite.  It  will,  however,  be  buried  beneath  more  sand 
with  the  jirst  fi-eshets  of  tbe  river.  The  two  main  springs  of  the  group  lie  to  the  west 
of  this  one.  Beyond  these  a  dark  ledge  of  limestone  projects  over  the  slopes  termi- 
nating the  timber  bench  some  20  feet  above  the  river.  The  first  of  these  two  springs 
is  a  bowl  with  a  wide  terraced  mound  of  great  beauty,  the  deposits  being  dense 
porcelain  like  travertine,  like  that  of  the  first  spring  noted.  The  spring  attracting 
most  attention  throws  up  a  splashing,  steaming  body  of  water  between  2  and  3  feet 
in  height.  The  smooth,  round  surface  of  the  bowl  is  a  snowy  white,  very  dense  and 
compact  travertine.  The  outlet  appears  as  a  break  in  a  marble  bowl  and  is  a  foot 
deep. 

Between  this  bowl  and  the  springs  to  the  east  of  it  there  is  a  hot-water  out- 
tiow  of  the  type  common  at  the  Mammoth  Hot  Springs.  The  spring  waters  have 
formed  mushroom  nodules  in  the  channel  and  a  fungus-shaped  border  about  the  waters. 
There  are  also  a  number  of  warm-water  springs  along  the  edge  of  the  stream,  but  the 
springs  issue  from  the  gravel  and  have  no  well-defined  basin  and  no  deposits. 

The  old  travertine  deposits  form  a  low  bench  about  5  or  6  feet  above  the  river, 
at  a  place  where  the  higher  bench  and  the  limestones  retreat  to  the  south.  The  area 
covered  does  not  exceed  one  fourth  of  an  acre.  The  actual  area  occupied  by  the 
sijrings  is,  however,  more  extensive,  for  following  the  grassy,  willow-covered  bench 
there  is  an  extension  of  the  travertine  level  to  the  west,  where  the  rocky  bluff  again 
comes  out  to  the  river. 

At  the  foot  of  a  higher  bench  back  of  these  low  hills  there  is  a  stream  of  hot 
water  which  flows  west  from  a  recess  in  the  meadow  to  the  base  of  the  cliff  and  along 
it  to  the  river.  The  stream  is  from  3  to  8  feet  wide  near  its  source.  The  water  is 
warm,  but  not  hot,  probably  not  over  120°  F.,  judging  from  the  algeous  growths,  but 
the  volume  of  water  is  very  considerable. 

The  photograph  from  which  the  illustration  is  made  is  a  view  down 
the  Snake  River  gorge  and  northwest  across  the  river  to  the  walls  of  rhyo- 
lite  on  the  opposite  side.  Forest  Creek,  which  runs  through  a  deep  trench 
in  the  rhyolite,  is  shown  on  the  north  side  of  the  river,  with  a  gently 
inclined  mass  of  lava  abruptly  terminated  along  the  gorge.  In  the  spring 
the  river  is  a  rushing  torrent,  subsiding  after  the  first  melting  of  the  snows, 
leaving  low,  broad  benches,  made  up  of  coarse  gravels  and  bowlders.  The 
view  was  taken  in  late  autumn,  when  the  water  stands  at  its  lowest  level. 


COULTER  OKEEK.  179 

UEGION  OF  COl  LTKU  CHEEK  AND  BOBCAT  RIDGE, 

Coulter  Creek. — Coiilter  C'vook,  l)of()re  eniptyinw'  into  Snake  lliver,  flows 
throufjli  an  open  basin,  and  is  yreatlv  aujiinented  by  the  drainage  of  two 
such  hvrge  streams  as  Harebell  and  Wolverine  creeks.  All  these  streams 
liave  brought  down  large  accumulations  of  drift  material,  and  the  underlying 
sedimentary  rocks  are  for  the  most  jjart  obscured  by  a  thick  mantle  of 
gravel,  sand,  and  tine  breccia.  The  mountain  slopes  surrounding  this  little 
basin  are  well  terraced,  and  five  sharply  defined  benches  rise  one  above  the 
other  to  a  height  of  nearly  200  feet.  Coulter,  Harebell,  and  Wolverine 
creeks  all  enter  this  basin  through  narrow  defiles  cut  in  breccia,  with 
perpendicular  walls  300  feet  in  height  in  places.  Coulter  Creek,  for  nearl^^ 
4  miles,  has  cut  its  way  through  this  breccia,  and  it  is  practically  impassable 
from  the  number  and  size  of  the  bowlders  which  lie  piled  up  along  the 
valley.  From  beneath  this  dark,  somber  breccia  Cretaceous  sandstones  and 
shales  crop  out  at  a  number  of  localities  and  on  the  west  side  of  Coulter 
Creek  extend  along  the  base  of  the  mountain,  with  the  breccias  lying  above. 

The  main  tributary  of  Coulter  Creek  from  the  west  has  cut  through 
the  breccia,  and  erosion  has  carried  it  away  from  the  mountain  slopes  so  as 
to  expose  Montana  sandstones  all  the  way  from  Huckleberry  Mountain  to 
Coulter  Creek.  In  the  region  of  Coulter  Creek  the  underl3^ing  sandstones 
possess  a  very  irregular  surface,  and  in  many  places  the  breccia  rests  upon 
them  as  a  thin  flow  or  crust.  The  sandstones  show  a  prevailing  dip  to  the 
southwest.  This  body  of  breccia  stands  by  itself,  completely  isolated  from 
the  vast  pile  of  breccias  of  Two  Ocean  Plateau  and  the  Absaroka  Range. 
It  is  very  irregular  in  outline  and  measures  about  8  miles  in  length, 
stretching  from  the  source  of  Coulter  Creek  northward  along  the  west 
slopes  of  Mount  Hancock. 

On  the  east  side  of  Coulter  Creek  the  breccia  attains  an  elevation  of 
8,500  feet,  and  on  the  slopes  of  Mount  Hancock  reaches  nearly  the  same 
elevation.  Throughout  the  entire  body  the  breccia  presents  much  the  same 
general  habit,  a  coarse,  firmly  compacted  agglomerate,  dark  brown  or  black 
in  color,  with  a  lighter-colored  cementing  material.  Some  portions  of  it  are 
exceptionally  coarse.  Fragments  of  well-rounded  gneiss  and  quartz  have 
been  observed  embedded  in  the  mass.  In  general  it  is  free  from  evidence 
of  bedding,  as  is  well  shown  in  the  exposures  along  the  main  stream.     At 


180  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Mount  Hancock  its  mode  of  weathering  is  well  brought  out  by  the  many- 
abrupt  walls  of  rough,  jagged  surface  and  numerous  deep  trenches  along 
the  mountain  side,  which  make  travel  very  difficult  and  well  nigh  impossible. 
The  breccia,  while  closely  resembling  the  imposing  mass  of  Two 
Ocean  Plateau,  and  probably  allied  to  it  in  age,  is  a  distinct  body,  having 
its  source  along  lines  of  displacement  west  of  the  Big  Game  Ridge  uphft 
and  the  continuation  northward  of  the  Bobcat  Ridge  fault.  It  was  the  result 
of  a  powerful  local  eruption  of  coarse  agglomerate,  imiform  in  its  composi- 
tion, violent  in  its  explosive  action,  and  oiih'  dimmed  in  interest  by  its  close 
proximity  to  the  larger  masses  of  the  Absaroka  Range.  It  consists  mainly 
of  pyroxene-andesite  and  basaltic  fragmental  material. 

Near  the  source  of  Coulter  Creek  broad  sheets  of  purple  lithoidal 
rhyolite  occur,  resting  directly  upon  these  basic  breccias.  On  the  west  side 
of  the  stream  there  occurs  an  isolated  body  of  rhyolite,  lying  on  the  breccia 
and  completely  surrounded  by  it.  This  exposure  is  interesting,  as  it  is 
evidently  a  remnant  left  by  erosion,  and  probably  at  one  time  was  con- 
nected with  the  larger  fields  to  the  east.  High  up  the  mountains  Coulter 
Creek  bifurcates  and  the  two  branches  encircle  a  broad  table  of  rhyolite 
which  lies  in  the  middle  of  the  mountain  valley.  It  is  not  known  on  what 
this  rhyolite  rests;  tlie  base  of  it  is  being  deeply  buried  beneath  an  accumu- 
lation of  glacial  drift  and  coarse  quartz  gravel,  derived  from  the  Eocene 
conglomerate  of  Pinj'on  Peak. 

Bobcat  Ridge. — Bobcat  Ridgc  is  one  of  the  marked  physical  features  of 
this  part  of  the  country,  standing  out  prominently  above  the  surrounding 
rido-es  by  reason  of  its  great  elevation.  The  ridge  trends  northwest  and 
southeast,  and  measures  about  6  miles  in  length.  It  is  a  singularly  narrow 
rido-e,  having  an  average  elevation  of  over  9,000  feet,  with  a  number  of 
peaks  scattered  along  the  summit,  which  attain  altitudes  of  9,500  feet  or 
more.  At  its  northern  end  it  is  connected  with  the  Wildcat  Peak  mass  and 
the  hio-h  country  around  the  head  of  Coulter  Creek.  At  its  southern  end  it 
falls  away  in  long  dreary  spurs  toward  the  valley  below,  lying  just  outside 
the  limits  of  the  area  shown  on  the  map.  Both  the  east  and  Avest  sides  of 
this  rido-e  are  abrupt  and  present  a  rather  dreary,  monotonous  aspect,  with 
little  standing  forest,  as  the  mountain  sides  over  large  areas  are  covered 
with  fallen  and  dead  timber. 

Greologically  Bobcat  Ridge  has  not  been  studied  much  in  detail.     A 


WOLVERINE  CREEK.  181 

fault  runs  along  the  west  base  ot"  tlic  lidge,  but  tlie  line  of  (lis])la(;eineut 
can  not  be  traced,  aiul  its  northern  end  is  lost  in  the  breccias  and  rhyolites. 
At  the  extreme  nortiiern  end,  near  tlu'  bend  of  (youlter  Creek,  there  is  a 
capjjing  of  rhyolite,  but  l)et\veen  this  rhyolite  and  the  higher  jjarts  of  the 
ridge  the  top  of  the  mountain  is  covered  with  loose  sand  and  coarse  gravel, 
derived  from  the  wearing  away  of  Pinyon  Peak  conglomerate. 

The  entire  ridge  is  apparently  made  up  of  yellowish-brown  sandstones 
of  the  Montana  formation.  In  places  the  sandstone  is  massive,  but  in  others 
it  is  well  bedded.  Wherever  observed  the  beds  dip  to  the  southwest,  and 
the  entire  ridge  is  probably  a  massive  block  of  upper  Ci-etaceous  sandstones, 
dipping  awa-\-  from  Mount  Hancock  and  Big  Game  Ridge. 

REGION  OF  WOLVERHSTE  CREEK. 

Wolverine  Creek  finds  its  source  high  up  on  the  west  slopes  of  Big 
Game  Ridge,  and  flows  westerly  for  9  miles,  joining  Coulter  Ci'eek  a  short 
distance  above  the  mouth  of  the  latter  stream.  Compared  with  other  high 
mottntain  streams  in  this  region  tributary  to  the  Siiake,  it  runs  through  a 
broad  open  valley,  rough  and  rugged  nuich  of  the  way,  but  intei'spersed 
with  green  meadows  and  wide  areas  of  alluvial  bottom.  The  mountains 
rise  high  above  the  stream,  the  valley  being  practically  shut  in  by  steep 
slopes  and  high  walls  on  all  sides. 

On  the  north  side  the  long  steep  spurs  of  Mount  Hancock  tower  above 
the  valley  for  1,500  feet  to  the  summit  of  Big  Game  Ridge.  On  the  south 
side  the  mountains  stand  out  witli  even  greater  abruptness,  and  are  more 
irregular  in  outline,  with  the  lower  slopes  largely  covered  with  timber  and 
heavy  accumulations  of  glacial  drift.  For  the  greater  part  of  the  distance 
the  valley  is  cut  in  sandstones  assigned  either  to  the  Montana  or  to  the 
Laramie  forma,tion.  Near  the  mouth  of  Wolverine  Creek  stands  a  grand 
escarpment  of  somber  breccia,  presenting  a  fine  section  in  many  ways 
typical  of  large  masses  of  this  rock. 

Beyond  this  wall  the  stream  bottom  is  impassable,  and  the  trail  ascends 
a  steep  hillside,  crossing  a  spur  of  the  mountain  for  2  miles  through  a  densely 
wooded  country  covered  with  soil  and  without  any  good  rock  exposures. 
This  spur  forms  a  part  of  the  main  mass,  lying  between  Coulter  and  Wolver- 
ine creeks,  and  as  exposed  on  both  streams  consists  mainly  of  basic  breccia 
resting  upon  a  base  of  Cretaceous  sandstone.  According  to  Prof.  J.  P. 
Iddings,  this  mass  is  capped  by  a  broad  table  of  rhyolite  3  miles  in  length, 


182  GEOLOG^Y  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

which  at  its  western  end  is  superimposed  upon  the  breccia.  The  north 
slope  of  this  ridge,  forming  the  south  wall  along  Wolverine  Creek,  consists 
mainly  of  bedded  sandstones  and  impure  shales  inclined  to  the  southwest, 
but,  owing  to  the  mantle  of  soil,  both  the  dip  and  the  strike  are  most 
difficult  to  determine. 

The  mountain  slopes  along  the  north  side  of  Wolverine  Creek  present 
a  remarkable  exposure  of  massively  bedded  yellow  sandstone,  with  prevail- 
ing dips  to  the  south  and  southwest — that  is,  toward  the  valley.  No  fossils 
have  been  obtained  from  these  beds,  but  they  have  been  assigned  to  the 
Montana  formation.  Higher  up  the  valley  they  pass  by  insensible  grada- 
tions into  beds  less  regular  in  their  sedimentation,  cai-rying  clays  and 
earthy  material  with  interbedded  ferruginous  sandstones.  The  latter  series 
of  beds,  from  their  lithological  habit,  have  been  placed  in  the  Laramie,  but 
without  any  sharp  lines  of  demarcation  between  the  two  formations.  They 
lie  conformably  on  the  older  beds  to  the  north  and  west,  and  pass  beneath 
the  valley,  dipping  into  the  ridge  on  the  opposite  side.  Due  north  of  Piu- 
you  Peak,  and  rising  as  an  abrupt  wall  on  the  south  side  of  Wolverine 
Creek,  stands  a  somewhat  prominent  hill,  several  hundred  feet  in  height.  It 
affords  an  excellent  exposure  across  characteristic  Laramie  strata  nearly 
200  feet  in  thickness.  These  consist  of  yellowish-brown  sandstones,  with 
interbedded  blue  and  black  clays,  rusty  sandstones,  and  thin  carbonaceous 
layers. 

Along  the  stream  bed  are  exposed  outcrops  of  five  distinct,  thin  seams 
of  impure  lignite  with  more  or  less  fragmentary  impressions  of  plant  remains. 
The  beds  strike  northwest  and  southeast,  and  dip  from  25°  to  30°  SW., 
passing  under  the  mass  to  Pinj^on  Peak. 

Higher  up  the  valley  at  several  localities  the  banks  along  the  .stream 
expose  arenaceous  blue  clays  and  black  shales  with  evidence  of  carbona- 
ceous material,  and  in  places  carrying  well-preserved  leaves.  These  beds 
also  dip  to  the  southwest.  Again,  on  the  divide  between  Wolverine  and 
Gravel  creeks,  and  due  east  of  Pinyon  Peak,  similar  beds  of  arenaceous 
clays  are  exposed  along  the  ravines  and  in  the  banks  cut  by  numerous  small 
streams.  These  beds  along  the  summit  of  the  pass  dip  to  the  southwest  and 
west  and  are  finally  lost  beneath  the  conglomerates  of  Pinyon  Peak.  The 
divide  between  these  two  creeks,  which  lies  at  an  elevation  of  8,500  feet 
above  sea  level,  is  cut  entirely  in  the  Laramie  sandstones. 


WOLVERINE  CREEK  FLORA.  183 

Wolverine  Creek  flora. — Theso  clays  5111(1  saiicly  betls  i)f  tlie  Laramie  have  so 
far  tailed  to  yield  any  evidence  of  an  invertebrate  fauna;  at  least  nothing 
has  been  found  sufficiently  well  preserved  to  determine  their  specific  char- 
acters. Plant  remains  have  been  obtained  from  several  of  these  localities 
bv  (liferent  members  of  tlu^  Survey,  but  mainly  by  Dr.  A.  C.  Gill,  who  was 
a  member  of  the  field  party  in  the  sununer  of  18S7.  Although  the  collec- 
tion embraces  few  species,  they  have  proved  to  be  highly  important,  not 
only  as  determining  by  the  evidence  of  organic  remains  the  Laramie  age  of 
these  beds,  but  also  as  indicating  the  geographical  distribution  of  Cretaceous 
plants  and  the  association  of  species  found  in  the  same  strata. 

Prof  F.  H.  Knowlton,  who  has  studied  these  plants,  has  determined 
seven  species,  which  he  has  described  in  detail,  with  illustrations,  iu  Chapter 
XIV  of  this  volume.  The  following  is  a  list  of  species  from  the  Wolverine 
Creek  beds,  extending  from  the  north  slope  of  Pinyou  Peak  to  the  low  pass 
at  the  head  of  Gravel  Creek:  Asplenium  haguei,  Onoclea  minima,  Paliurus 
minimus,  Sequoia  langsfonlii.  Viburnum  rotundifolium,  Trapa  micropliylla,  and 
Paliurus  sizyphoides. 

Of  these  sjjccies  the  first  three  are  described  for  the  first  time  by  Pro- 
fessor Knowlton.  P.  minimus  is  closely  related  to  P.  sizyphoides,  a  true 
Laramie  species  from  Black  Butte,  with  which  it  is  here  associated.  The 
last  four  species  are  also  found  in  the  Laramie  of  Black  Butte  and  Point  of 
Rocks.  Asplenium  haguei,  a  small  delicate  fern,  in  its  relationships  is  more 
closely  allied  to  certain  Cretaceous  species  from  Greenland  than  to  those  as 
yet  recognized  from  the  Rocky  Mountains  of  the  United  States.  Onoclea 
minima  is  also  closely  related  to  forms  from  Black  Butte  and  Point  of  Rocks. 
The  most  interesting  among  these  species  is  Trapa  microphylla,  which  is  here 
represented  by  several  fine  specimens.  It  was  first  described  from  Point  of 
Rocks,  Wyoming. 

This  identification  and  grouping  of  plants  carries  the  Laramie  flora  of 
central  Wyoming,  as  developed  at  Black  Butte  and  Point  of  Rocks,  north 
of  its  limits  as  heretofore  recognized.  The  Wolverine  Creek  beds  undoubt- 
edly belong  to  the  conformable  series  of  Cretaceous  sandstones  upturned 
by  the  orographic  movement  which  took  place  at  the  close  of  the  Laramie 
epoch.  They  lie  near  the  top  of  an  immense  series  of  sandstones  every- 
where uptilted  at  high  angles. 


184  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

REGION   OF  PINYOK  PEAK. 

Pinyon  Peak,  from  whatever  poiut  of  view  it  is  looked  at,  stands  out 
promiiieiitl}'  above  the  surrounding  country.  It  rises  boldly  above  Wol- 
verine Creek  for  over  2,000  feet,  and  for  more  than  1,500  feet  above  the 
connecting  saddles  which  relate  the  peak  to  the  mountains  both  east  and 
west.  To  the  south  the  country  falls  away  rapidly,  and  the  jjeak  presents 
a  still  more  isolated  appearance  when  seen  from  that  direction.  In  outline  it 
resembles  a  truncated  pyramid  rising  from  an  elevated  base.  Dense  timber 
covers  the  peak  on  all  sides  except  where  the  abrl^pt  cliffs  which  form  so 
conspicuous  a  feature  of  the  mountain  are  too  precipitous  to  permit  growth 
of  vegetation. 

Pinyon  Peak  attains  an  altitude  of  9,600  feet  above  sea  level.  The 
summit  is  flat  topped,  and  the  long  ridges  putting-  out  in  all  directions  from 
the  central  mass  resemble  a  very  slightly  inclined  plane,  with  occasional 
points  rising  above  the  general  level.  It  is  this  peculiar  feature  of  the 
peak  which,  from  a  distance,  gives  it  the  form  of  a  truncated  pyramid. 

Resting  upon  the  Laramie  rocks,  which  everywhere  form  the  base  of 
Pinyon  Peak,  comes  a  remarkable  deposit  of  coarse  conglomerate,  measur- 
ing nearly  600  feet  in  thickness.  This  conglomerate  forms  the  greater 
part  of  the  summit  of  the  peak  and  the  many  long  ridges  radiating  from 
the  central  body.  Nine-tenths  of  the  conglomerate  consists  of  smootli, 
highly  polished,  waterworn  material  of  various-colored  quartzites.  The 
prevailing  colors  are  red,  white,  and  yellowish  brown,  but  all  so  mingled 
tog'ether  as  to  give  a  general  tone  of  reddish  gray  to  the  abrupt  walls 
and  escarpments  which  form  so  prominent  a  feature  of  the  deposit.  This 
siliceous  niatei'ial  varies  from  gravel  to  coarse  pebbles  and  quartzite  bowl- 
ders measuring  10  and  12  inches  in  diameter,  although  the  largest  are 
by  no  means  common.  Much  of  the  conglomerate  is  indurated  and  held 
together  by  fine  sands  and  ferruginous  material.  Occasionally  thin  beds  of 
finable  sandstone  are  encountered  throughout  the  conglomerate,  but  they 
are  insignificant  in  amount  and  do  not  ajjpear  to  be  very  persistent  over 
any  great  distance,  occurring  as  lenticular  bodies  in  the  coarse  conglom- 
erate, then  as  well-defined  strata.  Everywhere  on  the  slopes  of  Pinyon 
Peak  the  beds  vary  greatly  in  thickness  and  in  continuity.  In  general 
it  may  be  said  that  the  conglomerate  formation  carries  more  sandstone 


PINYON  PEAK  CONGLOMERATE.  185 

near  the  base  tlian  it  does  liig-lier  up  in  the  de}M)sits.  Mingled  with  the 
(juartziti'  are  found  rounded  and  poHslied  ])el)bles  <»f  granite,  gneiss, 
argillite,  and  indurated  slates,  jjrobably  derived  from  Archean  and  pre- 
Candirian  land  surfaces.  Occasional  fragments  of  andesite  have  been 
found,  indicating-  a  volcanic  origin  for  some  of  the  detrital  material.  Such 
pebbles,  however,  are  hard  to  find  and  play  no  part  in  the  great  mass  of 
the  deposit.  Possibly  they  may  have  been  derived  from  the  capping  of  the 
breccia  foinid  on  the  top  of  Pinyon  Peak,  as  described  later.  Pebbles  of 
sandstone,  limestone,  and  other  sedimentary  rocks  have  been  picked  up  in 
the  conglomerate,  evidently  derived  from  neighboring  Paleozoic  and  Meso- 
zoic  sources.  Neai  the  base  of  the  conglomerate  waterworn  fragments  of 
coal  have  been  observed  associated  with  grav  sandstone  and  resembliusr 
that  known  to  occur  in  the  Laramie. 

Throughout  the  entire  mass  of  the  conglomerate  the  bowlders  present 
much  the  same  general  appearance  from  base  to  summit.  The  characteristic 
forms  of  the  long  ridges  radiating  from  the  culminating  mass  of  the  peak 
are  due  solely  to  the  peculiar  erosion  of  the  indurated  coarse  conglomerate. 
Erosion  has  worn  deep  recesses  into  the  very  core  of  the  jieak,  with  broad 
amphitheaters  encircled  by  nearly  perpendicular  walls  for  long  distances, 
absolutely  impossible  to  scale.  Along  their  tops  many  of  these  ridges  are 
mere  knife  edges,  barely  permitting  one  to  walk  in  safety.  In  places  the 
vertical  Avails  rise  for  over  300  feet  without  any  perceptible  change. 
Enormous  amounts  of  the  conglomerate  have  been  swej)t  away  by  erosion, 
the  material  Avhen  once  disintegrated  being  easily  transported.  Every- 
where the  lower  slopes  of  Pinyon  Peak  are  covered  by  loose  pebbles  and 
bowlders  brought  down  from  higher  elevations.  Coulter  and  Wolverine 
creeks  are  literally  clogged  up  with  quartzite  bowlders,  and  Gravel  Creek, 
draining  the  southwest  slopes  of  Pinyon  Peak,  derives  its  name  from  the 
huge  piles  of  reassorted  bowlders  which  line  the  valley  for  miles. 

For  many  years  the  gravels  along  Snake  River  and  Pacific  Ci'eek  in 
the  neighborhood  of  Jackson  Lake  have  been  known  to  yield  a  slight 
amount  of  gold  to  mining  prospectors,  but  not  in  remunerative  quantities. 
Evidences  of  gold  may  be  found  by  washing  with  a  pan  almost  anywhere 
in  the  streams  coming  down  from  the  conglomerate.  It  is  quite  likely  that 
this  gold  has  in  great  part  been  dei'ived  from  the  conglomerates  of  the 
Pinyon  Peak  formation.     In  many  places  the  indurated  conglomerate  and 


186  GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

associated  sands  are  distinctly  bedded.  They  lie  in  a  nearly  horizontal 
position,  or  at  a  low  angle  of  deposition,  resting  upon  the  upturned  edges 
of  tlie  Laramie  rocks. 

Local  faulting  and  displacement  in  the  conglomerate  may  be  observed, 
but  this  may  be  attributed  to  fracturing  and  shpping  of  limited  masses,  due 
to  the  wearing  away  of  underlying  beds  or  to  ice  filling  the  numerous  cracks 
and  ravines  found  in  the  rock  mass,  causing  landslides  on  a  grand  scale. 
That  the  conglomerate  has  been  subjected  to  great  pressm-e  and  movement 
within  the  mass  is  everywhere  apparent  l:)y  the  action  of  the  quartzite 
pebbles  on  one  another.  Field  study  of  these  pebbles  is  most  interesting 
from  the  curious  modifications  they  have  undergone  under  pressure.  In 
some  instances  they  are  flattened  and  rolled;  in  others  they  are  indented 
and  forced,  one  into  the  other.  Many  of  these  pebbles  are  cracked  and 
crushed,  in  some  cases  almost  ground  up,  so  great  has  been  the  pressure 
exerted  upon  them.  It  is  curious  to  observe  how  these  flattened,  almond- 
shaped  quartzite  pebbles,  with  the  pointed  end  fractured,  have  been  sharply 
cut  off"  by  dislocation  and  movement  of  the  mass.  Many  of  the  smaller 
fractured  pebbles  have  smooth  surfaces,  as  if  cut  off  by  some  sharp  instru- 
ment. A  vast  number  of  the  pebbles  show  a  peculiar  mottled  appearance, 
being  covered  by  white  spots  of  varying  size,  probably  produced  by  pres- 
sure of  the  pebbles  against  one  another. 

The  top  of  Pinyon  Peak  is  capped  by  a  heavy  bed  of  dark  basic  brec- 
cia, made  up  of  angular  fragments  in  every  way  resembling  the  breccia, 
ah-eady  described,  at  the  junction  of  Coulter  and  "Wolverine  creeks  on  the 
west  and  Two  Ocean  Plateau  on  the  east. 

According  to  Professor  Iddings,  who  studied  the  west  slo^ie  of  the 
peak,  the  breccia  is  300  feet  thick.  It  rests  directly  on  the  conglomerate, 
stretching  for  nearly  half  a  mile  along  the  east  face  of  the  mountain, 
projecting  out  like  a  lava  flow  over  several  of  the  characteristic  long  ridges. 
On  the  west  side  of  the  peak  it  stretches  westward  or  terminates  abruptly, 
with  the  conglomerate  coming  to  the  surface  from  beneath  the  breccias. 
The  conglomerate  was  evidently  deposited  before  the  laying  down  of  the 
breccia.  No  animal  or  vegetable  remains  have  as  yet  been  found  in  these 
conglomerates  and  indurated  sandstones,  consequently  no  definite  state- 
ment can  be  made  as  to  their  precise  age.  Tliat  they  are  younger  than  the 
Laramie  rocks  is  evident,  as  they  were  deposited  unconformably  upon  the 


riNYON  PEAK  OONGLOMEUATE.  187 

unturned  Cretaceous  sandstones.  In  all  probability  the  breccia  capping 
the  conoloiueratc  is  of  the  same  age  as  tliat  forming  the  great  mass  of  Two 
Ocean  IMatcau. 

It  is  quite  impossible  that  this  enormous  muss  of  basic  breccia  should 
have  been  poured  out  over  so  large  an  area  of  elevated  country  before  the 
deposition  of  the  conglomerate  and  not  have  furnished  a  considerable 
amount  of  material  to  the  latter  deposit.  A  discussion  of  the  age -of  this 
conglomerate  will  be  found  in  Part  I  of  this  monograph.  Evidence  is 
there  adduced  to  show  that  the  basic  breccia  of  this  region  is  in  all  prob- 
ability of  Miocene  age  and  followed  the  conglomerate.  The  conglomerate 
has  been  referred  provisionally  to  the  Eocene  period,  and  has  been  regarded 
as  a  distinct  geological  formation,  to  which  the  name  "Pinyon  Peak  con- 
glomerate" has  been  given,  after  the  locality  where  it  is  so  characteristically 
exposed. 

Southwest  of  Pinyon  Peak  and  connected  with  it  by  a  long  ridge  8,500 
feet  above  sea  level,  stands  an  east-west  ridge  whose  culminating  point 
attains  an  elevation  at  least  1,000  feet  higher.  This  prominent  ridge,  which 
has  never  received  any  distinctive  appellation,  measures  over  2  miles  in 
length,  standing  out  from  the  surrounding  country  like  a  broad  rampart. 
The  underlying  rocks  of  the  ridge  are  apparently  all  Cretaceous  sandstones 
and  have  been  referred  to  the  Laramie  formation,  although  it  is  quite  pos- 
sible that  Montana  strata  may  be  represented,  passing  by  insensible  grada- 
tions into  higher  horizons.  The  summit  of  this  ridge  is  capped  by  a  thick 
deposit  of  Pinyon  Peak  conglomerate,  which  was  evidently  at  one  time 
connected  with  the  main  body  of  Pinyon  Peak.  The  north  slopes  of  this 
ridge  are  covered  by  dense  vegetation  and  by  soil,  which  completely 
obscure  the  underlying  rocks.  On  the  south  slopes  the  sandstones  are 
exposed  for  a  long  distance,  but  near  their  base  the  glacial  drift  comes 
in  and  buries  everything  beneath  it. 

From  the  divide  at  the  head  of  Gravel  Creek  there  is  a  descent  of  over 
1,000  feet  in  5  miles,  the  country  south  of  Pinj'-on  Peak  falling  away  steadily 
toward  Pacific  Creek,  which  lies  just  south  of  the  limits  of  the  mapped 
area.  Grravel  Creek,  characteristically  named  from  the  gravels  which  line 
its  banks,  trends  due  south  along  the  west  base  of  Big  Game  Ridge.  A 
north-south  fault  probably  runs  along  the  west  base  of  the  ridge,  although 
its  course  has  never  been  determined.     The  area  of  country  lying  between 


188  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Big  Game  and  Bobcat  ridges  and  Pinyon  Peak  to  the  north  is  undei'laiu 
by  sandstone.  Over  the  sandstone  occur  large  areas  of  Pinyon  Peak  con- 
glomerate, and  much  of  the  country  is  strewn  with  iinassorted  coarse 
gravel,  derived  from  the  disintegration  of  the  more  compact  conglomerate. 
Accumulations  of  glacial  material  cover  large  areas.  It  is  a  broken,  hilly 
country,  with  great  diversity  of  topographic  features,  but  picturesque  and 
dotlednvith  groves  of  scattered  pine.  It  is  fairly  well  watered  by  numerous 
small  streams,  but  the  gravel  deposits  are  usualh'  dry. 

BIG   GAME  RIDGE. 

Big  Game  Ridge  is  a  narrow  mountain  uplift  about  15  miles  in  length, 
and  rises  abruptly  above  the  valley  of  Pacific  Creek  along  the  southern 
limit  of  the  forest  reservation,  with  a  trend  slightly  west  of  north  as  far  as 
the  slopes  of  Mount  Hancock.  From  the  latter  mountain,  the  culminating 
point,  the  trend  of  the  ridge  changes  to  northwest,  gradually  falling-  away 
toward  the  open  valley  near  the  junction  of  Heart  and  Snake  rivers.  The 
eastern  boundarj'  of  the  ridge  as  far  as  Crooked  Creek  is  defined  by  the 
Snake  River  fault,  which  approximately  coincides  with  the  course  of  Mink 
and  Fox  creeks,  the  fault  crossing  the  narrow  divide  separating  the  two 
streams.  From  Crooked  Creek  the  deeph'  trenched  but  narrow  valley  of 
Snake  River  defines  Big  Game  Ridge  from  Chicken  Ridge. 

Geologically  Big  Game  Ridge  is  formed  mainly  of  Ci'etaceous  sand- 
stones, singularly  uniform  in  color  and  texture  from  one  end  of  the  ridge 
to  the  other.  The}-  have  been  referred  to  the  Montana  and  Laramie  forma- 
tions. In  broad  masses  at  certain  localities  the  two  formations  may  readily 
be  distinguished  b}^  their  lithological  habit,  l^ut  they  resemble  each  other 
so  closely  near  their  junction  that  any  line  of  demarcation  must  of  necessity 
be  drawn  somewhat  arbitrarily.  In  the  great  thickness  of  Montana  sedi- 
ments developed  here,  coarse  yellowish-gray  sandstones  are  everywhere 
the  prevailing  rock,  and  nowhere  has  the  Pierre  shale  been  recognized  as 
such  by  its  lithological  habit.  Evidences  derived  from  organic  remains 
ai'e  entirely  wanting.  Rhyolite  skirts  the  ridge  in  a  number  of  ])laces,  and, 
as  described  farther  on,  caps  the  very  summit  of  Mount  Hancock,  and 
basic  breccias  cover  the  lower  slopes  north  of  Harebell  Creek. 

Gravel  Peak. — Tliis  pcak  Is  situatcd  3  miles  north  of  the  southern  limit 
of  the  mapped  area,  midway  between  Gravel  and  Mink  creeks.     It  has  an 


BIG  GAME  KIDGE.  189 

elevation  of  9,600  feet  above  sea  level,  and  is  the  culminating-  point  of  the 
southern  end  of  the  ridge.  Its  interest  Hes  mainly  in  the  conglomerates, 
which  form  the  upper  400  feet  and  which  rest  upon  the  mountain  in  much 
the  same  wa}'  as  they  do  upon  Pinyon  Peak.  The  gravels  are  in  every 
way  identical,  and  belong  without  doubt  to  the  same  horizon.  Abrupt 
walls  of  this  i-onglomerate  face  east  and  north,  oftering  good  expo.sures 
across  coarse  gravels  with  polished  and  crushed  i)ebbles  held  firmly  together 
by  sands.  They  rest  directly  ujion  Laramie  sandstones,  which  dip  to  the 
east  at  low  angles,  and  near  the  base  of  the  ridge  abut  unconformably 
against  Madison  limestone  lying  along  the  east  side  of  the  Snake  River  fault. 

Isolated  patches  of  Pinyon  Peak  beds,  left  by  erosion,  rest  upon  sand- 
stones west  of  Gravel  Peak.  They  lie  at  different  elevations,  but  their 
position  may  be  due  to  a  series  of  small  parallel  faults  found  along  that  side 
of  the  ridge.  The  block  of  sandstone  north  of  Gravel  Peak  Ridge  and  due 
east  of  Pinyon  Peak  presents  a  northward  continuation  of  the  same  Creta- 
ceous strata.  The  ridge  trends  a  few  degrees  east  of  north  and  west  of 
south,  with  beds  dipping  at  low  angles  to  the  east.  Beds  typical  of  the 
upper  portion  of  the  Laramie  make  up  the  entire  ridge.  The  sandstones 
are  rusty  brown  in  color,  with  numerous  thin  layers  of  ferruginous  material 
interbedded  with  friable  white  sands.  Clay  bands  and  thin,  shaly,  impure 
sandstone  with  evidence  of  cross  bedding  characterize  both  slopes. 

Fragmental  and  imperfect  plant  remains  lie  scattered  over  the  surface, 
and  certain  strata  seem  to  carry  a  considerable  amount  of  carbonaceous 
material.  Specimens  of  leaves  and  twigs  were  collected,  indicating  a  vig- 
orous flora,  but  all  too  imperfect  to  pemiit  of  specific  identification.  Over 
the  top  of  the  ridge  are  strewn  smoothly  polished  quartzite  pebbles  derived 
from  the  Pinyon  Peak  conglomerate,  but  no  beds  of  the  same  were  found 
in  place.  North  of  the  pass  from  Wolverine  Creek  to  Fox  Creek  the  ridge 
still  shows  the  lithological  habit  of  the  Laramie  sandstones.  At  the  north 
end  the  massive  white  beds  dip  from  5°  to  10°  SE.;  in  fact,  all  the  beds  in 
this  region  dip  to  the  southeast. 

The  line  of  demarcation  between  the  Montana  and  Laramie  formations 
is  drawn  along  the  southeastern  slopes  of  Mount  Hancock,  as  will  be  seen 
by  reference  to  the  map. 

The  basal  rocks  of  the  Laramie,  as  thus  defined,  trend  in  a  general 
northeasterly    direction.     Starting  at  the  south  base  of  Mount  Hancock, 


190     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

in  the  valley  of  Wolverine  Creek,  tliey  cross  the  summit  of  Big  Game 
Ridge,  and  pass  down  the  steep  east  slopes,  where  they  are  well  exposed  on 
both  sides  of  Snake  River  just  below  the  mouth  of  Crooked  Creek.  It  can 
not  be  said  with  any  degree  of  assurance  that  this  line  is  correctly  laid 
down,  but  no  sandstones  to  the  north  or  west  of  it  have  been  recognized 
as  possessing  the  lithological  characters  of  the  Laramie.  In  the  great 
thickness  of  sedimentary  sandstones  represented  in  the  several  orographic 
blocks  it  is  possible  that  Laramie  beds  may  occur,  Avithout  geological  evi- 
dence as  to  their  age. 

Mount  Hancock. — Mouut  Haucock  is  uot  only  the  most  prominent  mountain 
of  Big  Game  Ridge,  but  it  stands  out  as  one  of  the  most  commanding- 
points  along  the  southern  border  of  the  Park.  It  was  named  after  General 
Hancock  by  Maj.  J.  W.  Barlow,  who  ascended  the  peak  in  August,  1871. 
On  a  clear  day  the  view  from  the  summit  is  unsurpassed,  either  for  detail 
of  topographic  features  immediately  beneath  or  for  the  more  distant  pano- 
ramic outline.  It  commands  the  Tetons,  the  dominant  peaks  of  the  Wind 
River  Range  stretching  far  southward,  the  entire  west  face  of  the  Absarokas, 
the  Park  Plateau  with  its  great  lakes,  the  Snowy  Range  to  the  north,  and 
the  Gallatin  and  Madison  ranges  to  the  west. 

Mount  Hancock  rises  above  Snake  River  at  its  east  base  for  over  2,000 
feet,  and  above  the  valley  of  the  Snake  at  its  west  base  for  2,500  feet. 
The  greater  part  of  the  mountain  consists  of  yellowish-gray  and  white 
massively  bedded  sandstone,  which  extends  to  within  400  feet  of  the 
summit.  All  the  beds  forming  the  upper  portion  of  the  mountain  have 
been  assigned  to  the  Montana  formation,  although  no  organic  remains  have 
been  obtained  from  them.  The  southeastern  slopes  offer  the  best  exposures 
of  these  rocks,  which  dip  to  the  southeast.  It  is  estimated  that  there  are 
over  3,500  feet  of  sandstones.  On  the  nari'ow  ridge  of  sandstone  just  south 
of  the  summit  the  beds  strike  north  and  south  and  dip  30°  W.  The 
western  spurs  of  the  mountain  are  largely  covered  by  forests  and  glacial 
drift,  rendering  it  difficult  to  obtain  good  exposures,  but  the  beds  for  the 
most  part  apparently  dip  west.  North  of  Harebell  Creek  basic  breccias 
similar  to  those  found  on  Coulter  and  Wolverine  creeks,  and  part  of  the 
same  mass,  extend  along  the  west  base  of  Mount  Hancock.  They  present 
a  most  irregular  outline,  the  higher  portions  reaching  an  altitude  of  over 
8,000  feet  above  sea  level. 

On  the  summit  of  Mount  Hancock  a  capping  of  dark  rhyolite  stands 
out  boldly,  in  contrast  with  the  yellowish  underlying  sandstones.     It  rises 


CHICKEN  KIDGE.  '  191 

over  400  feet  in  jjrecipitoius  walls,  faciiif^-  north  ;uul  east,  l)nt  on  the  south 
falls  awav  witli  drliris  slopes,  permittinj^'  ascent  to  the  summit.  Tlie  mass 
has  a  slight  inclination  to  the  east,  and  the  greater  part  of  it  is  lithoidal, 
very  brittle,  and  jointed  in  thin  fissile  layers.  At  a  distance  on  the  slopes 
it  resembles  a  d(jbris  pile  of  cherty  indurated  argillites.  This  ntck  is  dark 
gray  in  color,  with  small  phenocrysts  of  feldspar  and  grains  of  quartz. 
Obsidian  and  gray  and  red  pumices  are  well  shown  here,  with  the  varying 
nioditications  found  elsewhere  in  the  Park  and  described  in  detail  in 
Chapter  X  of  this  volume.  Mount  Hancock  is  perhaps  remarkable  for  the 
variations  in  color  of  its  obsidian.  Black,  brown,  and  various  shades  of 
red  are  noticeable,  and  some  of  them  Avhen  highly  polished  are  singularly 
brilliant.  It  is  this  dark,  turret-like  mass  of  rhyolite  that  makes  Mount 
Hancock  so  conspicuous  a  landmark  over  the  Park  region.  The  great 
elevation  and  complete  isolation  of  this  small  body  of  rhyolite  are  by  no 
means  easy  to  explain. 

North  of  Mount  Hancock  the  slopes  of  Big  Game  Ridge  fall  away 
rapidly  for  4  miles  in  long  timber  ridges,  mostly  buried  beneath  glacial 
drift  and  soil.  No  rock  exposures  were  observed  other  than  the  Montana 
sandstones  and  the  low  rhyolite  hills  which  border  the  uplifted  sedimentary 
beds. 

CHICKEN  RIDOB. 

Chicken  Ridge  presents  a  narrow  north-south  chain  of  mountains 
about  12  miles  in  length.  It  is  a  prominent  and  persistent  orographic 
block,  with  several  culminating  points  between  9,000  and  9,600  feet  above 
sea  level.  Over  the  greater  part  of  this  area  the  mountain  slopes  are  well 
timbered  and  well  watered.  The  southern  end  of  Chicken  Ridge  rises 
abruptly  on  the  east  side  of  Snake  River  at  its  junction  with  Crooked 
Ci'eek,  nearly  due  east  of  Mount  Hancock.  Along  its  east  base  the  ridge 
is  sharply  defined  from  Two  Ocean  Plateau  by  the  valleys  of  Crooked 
and  Grouse  creeks  and  the  narrow  north-south  depression  lying  between 
the  two  streams. 

The  Snake  River  fault,  which  is  described  later  in  this  chapter,  follows 
the  course  of  these  streams,  and  the  marked  contrast,  both  geologically 
and  topographically,  between  the  opposite  sides  of  the  fault  serves  to 
accentuate  the  eastern  boundary  of  the  ridge.  Northward  Chicken  Ridge 
projects  into  Yellowstone  Lake,  and  its  gentle  slopes  along  the  base,  with 
broken,  accidented  hills  rising  above  them,  form  the  picturesque  shores  of 


192  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  south  arm  of  tlie  lake.  The  deeply  trenched  valley  of  Snake  River 
limits  the  mountains  on  the  south  and  southwest,  and  the  rhyolites  of  the 
Park  Plateau,  stretching  from  Heart  River  to  Yellowstone  Lake,  submerge 
between  an  accumulation  of  lava  the  western  flanks  of  the  mountains  to 
heights  varying  from  8,000  to  8,500  feet. 

Topographically  Chicken  Ridge  is  closely  related  to  Big  Game  Ridge, 
the  latter  trending  off  to  the  northwest,  while  the  former  has  a  nearly 
north-south  course.  Geologically  the  relationship  is  still  closer,  and  the 
Cretaceous  strata  of  Big  Game  Ridge  can  be  easily  traced  crossing  the  river 
at  several  localities.  This  is  speciall}'  well  shown  at  the  southern  end  of 
Barlow  Peak,  just  north  of  Crooked  Creek 

Barlow  Peak. — Barlow  Peak  is  named  by  the  writer  in  honor  of  Maj.  J.  W. 
Barlow,  of  the  Engineer  Corps  of  the  Army.  He  conducted  the  first  official 
exploration  to  the  headwaters  of  Snake  River  in  1871.  The  peak  attains 
an  elevation  of  9,500  above  sea  level,  and  rises  1,500  feet  above  the  river. 
It  forms  a  well-defined  mountain  block  between  Crooked  and  Sickle  creeks, 
the  former  stream  encircling  its  southern  base,  and  the  latter  cutting  a  deep 
trench  directly  across  Chicken  Ridge,  flowing  into  Snake  River  4  miles 
farther  downstream. 

Just  below  the  mouth  of  Crooked  Creek,  beds  assigned  to  the  Larajnie 
are  found  on  both  sides  of  Snake  River,  dipping  to  the  sovitheast  and  east. 
They  ci'oss  the  spur  of  the  mountain,  continuing  eastward  until  lost  in  the 
accumulation  of  drift,  and  are  finally  cut  off  by  the  Snake  River  fault.  The 
Laramie  sandstones  reach  nearly  to  the  summit,  and  along  the  crest  of  the 
ridge  are  underlain  by  yellowish-gray  sandstones  similar  to  those  found  high 
up  on  the  slopes  of  Mount  Hancock.  The  Montana  sandstones  cap  the 
summit  of  Barlow  Peak,  aiid  along  the  east  slope  dip  10°  to  15°  E.  From 
this  point  they  can  be  traced  northward  across  Sickle  Creek,  still  inclined 
in  the  same  direction. 

Passing  down  Sickle  Creek  the  underlying  beds  gradually  grade  into 
thinly  bedded  sandstones,  limestones,  black  shales,  and  argillaceous  sand- 
stones, and  are  well  exposed  on  both  sides  of  Snake  River.  Lithologically 
these  beds  bear  the  closest  resemblance  to  the  sedimentation  of  the  Colorado 
formation  found  elsewhere.  The  thickness  of  these  black  clay  shales  and 
interbedded  sandstones  has  been  estimated  at  600  feet.  On  the  north  liank 
of  Snake  River,  about  a  quarter  of  a  mile  above  the  mouth   of   Sickle 


CHICKEN  ItlDUE.  193 

Creek,  there  were  found  in  the  shale  a  cross-bedded  sandstone  3  feet  in 
thickness,  carrying'  a  number  of  characteristic  Colorado  fossils.  From  this 
collection  Mr.  T.  AV.  Stanton  has  identified  the  following  species:  Inoceramus 
tiudahundus,  I.  uinhonatus,  I.  flaccidus,  I.  acutepUcatus,  BacuUtcs  asper,  Sca- 
phifcs  ventricosus.  Along  Snake  River  the  base  of  the  Colorado  formation 
is  nowhere  exposed;  consequently  no  estimate  can  be  made  of  its  thickness; 
but  there  ai'e  at  least  400  feet  of  fissile  impure  sandstones  and  limestones 
above  the  heavy  shale  belt  assigned  to  the  Montana. 

The  Colorado  formation  extends  along  Snake  River  for  more  than  £ 
miles,  the  deep  trench  of  the  river  exposing  a  sharp  anticline  in  the  shales. 
A  mile  below  the  mouth  of  Sickle  Creek,  on  the  northwest  bank,  occurs  an 
exposure  of  blue  clays  inclined  nearly  70°  SW.,  while  half  a  mile  upstream 
the  beds  dip  30°  NE.  Near  the  point  where  the  Colorado  fauna  was 
obtained  the  shales  dip  from  10°  to  15°  NE.  Along  the  south  and  west 
banks  of  the  river  the  Colorado  beds,  on  the  west  side  of  the  anticline, 
rapidly  pass  beneath  the  Montana  sandstones  at  the  base  of  Big  Game 
Ridge.  On  the  bottom  of  Heart  River,  the  stream  having  cut  completely 
through  the  flow  of  rhyolite,  there  is  an  exposure  of  dark  clay  shale 
which  has  been  referred  to  the  Colorado  and  may  prove  to  be  an  extension 
northward  of  the  Cretaceous  shales  exposed  between  Sickle  and  Crooked 
creeks. 

Between  Sickle  and  Outlet  creeks  Chicken  Ridge  is  made  up  mainly 
of  yellowish-gray,  brown,  and  white  sandstones,  which  in  their  lithological 
habit  closely  resemble  those  found  on  Mount  Hancock  and  Barlow  Peak. 
Along  the  southern  slope  the  upper  beds  are  a  very  dense  steel-gray  rock. 
North  of  Coulter  Creek  the  beds  strike  obliquely  across  the  ridge,  but 
northward  trend  with  the  ridge  in  a  nearly  north-south  direction.  The 
general  dip  varies  from  20°  to  30°  E. 

South  of  Overlook  Mountain  the  sandstones  are  well  exposed,  and  are 
incHned  30°  E.,  toward  Grouse  Creek,  with  evidences  of  local  faultino- 
accompanied  by  variations  in  dip.  Underlying  these  beds  on  the  west  side 
of  Chicken  Ridge  fissile  sandstones  with  interbedded  arenaceous  shales 
prevail.  Lithologically  these  latter  beds  resemble  the  Pierre  shales  of  the 
Montana,  and  have  been  con-elated  with  them,  although  no  evidences  of 
organic  remains  were  secured.  They  form  the  slopes  until  obscured  by  the 
rhyolite  flows,  which  attain  elevations  of  between  8,200  and  8,300  feet  above 

MON  XXXII,  PT   II 13 


194  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

sea  level.  A  sharp  contrast  is  seen  between  the  steep  rounded  slopes  of 
the  sandstone  and  the  irregular  outline  of  rhyolite.  The  latter  is  marked 
by  long,  naiTOw  drainage  channels,  with  steep  bluffs  on  the  west  side, 
parallel  to  the  valley  of  Heart  River.  These  bluffs  stand  out  from  20  to 
50  feet  above  the  depression.  The  intervening  ravines  are  the  result  of 
ice  movements  and  are  occupied  by  small  ponds  and  meadows  carved  out 
of  glacial  drift. 

OUTliET  CANYON. 

This  impressive  gorge  cuts  a  deep,  broad  passage  completely  through 
Chicken  Ridge.  In  the  strict  use  of  the  word  it  is  a  true  canyon,  quite 
unlike  any  other  canyon  or  drainage  channel  in  this  part  of  the  country, 
and  is  one  of  the  most  interesting  geological  features  to  be  found  within  the 
Park.  It  affords  an  instructive  section  across  the  range  from  Grouse  Creek 
to  Heart  River,  with  the  Montana  sandstones  constituting  the  center  of  the 
ridge,  flanked  on  both  sides  by  rhyolite  hills.  Overlook  and  Channel 
mountains,  on  opposite  sides  of  the  canyon,  form  a  part  of  the  same  mono- 
clinal  uplift,  the  strata  striking-  with  the  ridge. 

The  interesting  feature  about  Outlet  Canyon  is  that  it  at  one  time 
served  as  the  discharge  for  the  waters  of  Yellowstone  Lake.  This  mag- 
nificent sheet  of  Avater,  which  now  flows  northward  and  drains  to  the 
Atlantic  through  the  famous  Yellowstone  Canyon,  formerly  discharged 
by  way  of  the  south  arm  through  Outlet  Canyon  to  Snake  River  and 
thence  onward  to  tlie  Pacific.  The  discovery  of  Ovitlet  Canyon  as  an 
ancient  drainage  channel  for  Yellowstone  Lake  was  made  by  the  writer  in 
1889.  For  several  years  he  had  been  firmly  convinced,  by  geological 
reasoning  that  seemed  unanswerable,  that  this  grand  lake  at  one  time 
must  have  discharged  southward,  and  consequently  into  the  Pacific.  All 
attempts  to  locate  such  outlet  proved  futile  till  the  autumn  of  that  year. 
It  was  hidden  by  dense  forests,  obscured  by  glacial  drift,  and  abandoned 
as  a  waterway.  After  the  discovery  of  this  old  and  neglected  channel  all 
fresh  observations  tended  to  strengthen  and  confirm  the  arguments  that  the 
lake  formerly  found  its  outlet  to  the  south.  In  the  chapters  treating  of 
the  physiographic  features  of  the  Park,  in  Part  I  of  this  monogra^ih,  the 
problems  connected  with  the  ancient  drainage  of  Yellowstone  Lake  are 
discussed  at  some  length  and  Outlet  Canyon  is  described  in  detail  in  its 


ANCIENT  OUTLET  OF  YELLOWSTONE  LAKE.  195 

bearin<?  upon  the  subject.  In  the  present  chapter,  therefore,  it  is  only 
necessar)'  to  refer  to  a  few  facts  as  given  there,  so  far  as  they  relate  to 
the  geological  features  of  Chicken  Ridge. 

PI.  XXV  is  a  reproduction  from  a  photograph  of  the  meadow  of 
Outlet  Canyon.  The  view  is  taken  from  the  top  of  a  low  glacial  mound, 
looking  eastward  toward  the  ci-est  of  the  ridge.  The  Cretaceous  rocks 
forming  the  walls  of  the  canyon  are  shown  on  the  right-hand  side  of  the 
picture,  the  bare  white  outcrop  marking  the  contact  between  the  sand- 
stone and  rhyolite.  Along  the  north  wall,  shown  in  the  picture,  the  abrupt 
precipice  consists  of  rhyolite,  rising  inore  than  150  feet  above  the  valley. 
The  densely  wooded  slopes,  as  depicted  in  the  illustration,  represent  fairly 
well  lai-ge  areas  of  the  Park,  covered  by  a  vigorous  growth  of  lodge-pole 
pine  (P'niKS  mnrrayana),  which,  although  of  poor  quality  as  timber,  meets 
every  requirement  in  preserving  the  soil  from  being  washed  away  by 
freshets  and  in  protecting  the  snows  from  the  hot  suns  and  dry  winds. 

Outlet  Canyon  is  a  broad,  deep  gorge,  and  thi'oughout  a  long  period 
of  time  evidently  served  as  the  channel  for  a  rapid,  powerful  stream  carry- 
ing a  large  volume  of  water.  To-day  its  bottom  is  a  flat,  grassy  meadow 
with  dark,  rich  soil,  through  which  meanders  with  sinuous  course  a  slug- 
gish brook  of  dark,  unattractive  water.  Tall,  coarse  grasses  and  low 
growths  of  willows  line  the  Ijrook. 

During  the  ice  period  Outlet  Canyon  was  undoubtedly  occupied  by  an 
extensive  glacier.  Stretching  across  the  bottom  of  the  canyon,  between 
Overlook  and  Channel  mountains,  lies  an  old  terminal  moraine,  whose 
matei-ial  consists  mainly  of  sandstone  and  rhyolite,  Avith  occasional  frag- 
ments of  andesite  and  basalt.  Tliis  obscure  morainal  heap  to-day  marks 
tlie  course  of  the  continental  watershed,  serving  as  a  barrier  between  the 
waters  of  the  Atlantic  and  those  of  the  Pacific.  From  this  insignificant 
and  unassorted  heap  of  detrital  material  a  small  stream  having  scarcely  any 
eroding  force  has  cut  itself  a  channel  in  the  glacial  drift,  but  nowhere  has 
it  penetrated  to  the  underlying  rock.  Never  since  the  retreat  of  the  ice 
has  it  been  anything  more  than  a  mere  rivulet.  The  glacial  material,  over- 
lain by  alluvial  deposits,  completely  occupies  the  bottom  of  the  valley,  and 
only  along  the  abrupt  walls  of  the  canyon  are  Cretaceous  rocks  exposed. 
This  sluggish  stream,  which  one  can  easily  jump  across,  emerges  from  the 
canyon  through  a  growth  of  pines,  and  comes  out  into  the  open  valley  of 


196     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Grouse  Creek  on  the  broad  90-foot  lacustrine  bench  of  the  older  and  larger 
Yellowstone  Lake. 

On  the  west  side  of  the  moraine  across  which  runs  the  continental 
divide  there  is  an  abrupt  descent  to  a  characteristic  glacial  lake.  From 
this  lake  flows  Outlet  Creek,  the  sluggish  stream  before  mentioned.  Across 
the  west  end  of  Outlet  Canyon  there  stretches  a  somewhat  formidable 
barrier  in  the  shape  of  a  moraine  Upon  reaching  this  bai-rier  the  stream 
deviates  to  the  northwest  and  cuts  its  narrow  channel  through  the  gravel 
under  the  north  wall  of  the  canyon.  Descending  rapidly  through  the 
accumulated  drift,  it  comes  out  once  more  upon  the  old  river  channel,  and 
soon  pours  its  waters  into  Heart  River  and  out  through  the  Snake  to  the 
Columbia.  ^ 

CHAKNEL  MOUNTAIN. 

Outlet  Canyon  north  of  Chicken  Ridge  presents  many  of  the  same 
physical  features  as  those  noted  to  the  southward,  and  offers  no  special 
points  of  geological  interest.  A  conical  hill  which  forms  the  southern  spur 
of  Channel  Mountain  affords  an  excellent  bird's-eye  view  of  Outlet  Canyon, 
its  mural  face  rising  high  above  the  river  channel. 

From  this  hill  the  Montana  formation  can  be  traced  northward  along 
the  summit  of  Channel  Mountain,  a  conspicuous  and  timbered  point  9,000 
feet  above  sea  level.  The  sandstones  of  Channel  Mountain  do  not  differ 
essentially  from  those  of  Mount  Hancock  and  Barlow  Peak.  From  this 
culminating  peak  Chicken  Ridge  gradually  falls  away  toward  the  lake  on 
the  north  and  east. 

Lacustrine  deposits  skirt  the  lake  shore,  attaining  an  elevation  of  nearly 
8,000  feet  above  sea  level.  Still  above  this  in  certain  localities  come  the 
remnants  of  glacial  drift,  resting  indiscriminately  upon  rhyolite  and  Creta- 
ceous sandstones.  Rhyolite  encircles  the  ridge  on  all  sides,  while  the  cen- 
tral body  consists  of  the  ever-persistent  Montana  sandstone. 

FLAT   MOUNTAIN. 

It  may  be  well  to  call  attention  to  the  fact  that  near  the  lake  shore, 
at  the  northwest  base  of  Flat  Mountain,  there  comes  to  the  surface  from 
beneath  the  rhyolite  an  outcrop  of  sedimentary  rocks,  exposed  by  the  erosion 
of  the  lava  along  the  southern  prolongation  of  Flat  Mountain  arm.     A  short 


TWO  OCEAN  PLATEAU.  197 

distance  above  the  lake  level  occurs  an  outcrop  of  compact  blue  quartzite, 
for  the  most  part  obscured  by  soil  and  vegetation.  It  has  been  refen-ed  to 
the  Sheridan  quartzite  of  the  Algonkian  period.  Resting  unconformably 
upon  the  Sheridan  (juartzite  is  a  series  of  limestones,  marls,  and  sand- 
stones of  the  Ellis  formation.  They  extend  up  the  slope  of  Flat  Mountain 
for  about  300  feet,  where  they  are  finally  lost  beneath  the  rhyolite.  In  the 
limestone  were  found  Rhynchouella  and  Camptonectes.  The  characteristic 
Ellis  sandstone  has  furnished  the  following  species:  BhynchoneUa  gnath- 
opliora,  Camptonectes  pertetmistnatus,  Avicula  wyomingensis. 

WEST  BASE   OF  TWO   OCEAN  PLATEAU. 

Between  Big  Grame  and  Chicken  ridges  and  the  top  of  the  broad 
elevated  mass  of  Two  Ocean  Plateau  lies  a  comparatively  narrow  strip  of 
country  characterized  by  distinctive  and  peculiar  features.  It  presents 
an  aspect  entirely  dilferent  from  that  of  the  country  westward,  and  stands 
out  in  strong  contrast  to  it,  both  in  its  geology  and  in  its  topography. 
The  Cretaceous  sandstones  which  have  been  so  persistent  a  feature  of  the 
country  are  wanting  and  otlier  and  older  rocks  come  to  the  surface. 

Snake  River  fault. — This  remarkable  fault,  to  which  allusion  has  already  been 
made,  sharply  defines  geologically  the  east  base  of  Big  Game  Ridge  and 
Chicken  Ridge  from  the  country  to  the  east.  The  line  of  the  fault  can  be 
traced  for  18  miles  from  the  head  of  Grouse  Creek  southward,  beyond 
the  limits  of  the  mapped  area,  until  obliterated  by  overlying  masses  of 
Tertiary  breccias.  For  this  entire  distance  the  west  side  of  the  fault 
exposes  only  Montana  and  Laramie  sandstones.  In  places  the  sandstones 
are  obscured  by  glacial  accumulations.  Occasional  outbursts  of  basalt  are 
met  with  along  the  line  of  displacement,  which  coincides  with  the  line  of 
least  resistance.  On  the  east  side  of  the  fault  either  Madison  limestone 
of  the  Carboniferous  or  the  Teton  beds  of  the  Juratrias  are  brought  to  the 
surface,  but  they  are  by  no  means  so  persistently  exposed,  their  continuity 
being  broken  by  outlying  masses  of  basic  breccia  from  Two  Ocean  Plateau. 
Contacts  between  the  Paleozoic  and  Mesozoic  rocks  are  admirably  shown 
all  the  way  from  Grouse  Creek  to  Crooked  Creek.  At  the  latter  locality 
there  is  a  dense  black  basalt  whose  outlines  are  partially  obliterated  by 
loose  alluvial  deposits,  but  the  large  detached  bowlders  and  black  basaltic 
soil  help  to  define  its  area  along  the  line  of  the  fault.     Still  farther  south, 


198  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

in  the  valley  of  Snake  River,  similar  basalts  have  broken  out.  Along'  Fox 
Creek  the  fault  is  not  so  readily  traced,  owing  to  the  broad  benches  of 
morainal  drift  and  the  occurrence  of  basic  breccia  which  lie  on  both  sides 
of  the  displacement. 

These  breccias  are  well  exposed  in  the  more  recent  cuts  along  Fox 
Creek,  and  in  every  way  resemble  those  found  on  Two  Ocean  Plateau. 
They  are  andesitic  breccias,  firmly  held  together  by  finer  material,  generally 
colored  i-ed  from  the  oxidation  of  the  ferruginous  material.  West  of  Fox 
Creek,  on  the  slope  of  Big  Game  Ridge,  is  an  outcrop  of  rhyolite,  interesting 
from  the  fact  of  its  being  the  most  easterly  exposure  of  that  rock  west  of 
Two  Ocean  Plateau.  This  rhyolite  is  evidently  a  remnant  of  a  much  larger 
body  of  purplish-gray,  normal  rock,  like  most  of  that  seen  on  Flat  Mountain. 
It  disintegrates  readily  into  rhyolitic  gravel,  in  rather  strong  contrast  to  the 
weathered  and  crumbling  sandstone. 

Alona"  Mink  Creek  the  fault  contact  between  the  Cretaceous  and  Car- 
boniferous  is  strikingly  shown,  a  great  thickness  of  both  rocks  being  well 
developed,  Mink  Creek  having  cut  deeply  into  the  Madison  limestone. 
Pacific  Creek  below  Mink  Creek  also  marks  the  fault  line  until  it  passes 
beyond  the  limits  of  the  mapped  area. 

Pacific  Creek. — Tliis  strcam,  which  has  its  source  along  the  continental 
divide,  has  cut  for  itself  a  broad  channel  on  both  sides  of  the  older  valley. 
The  breccias  have  been  worn  away,  exposing  a  body  several  hundred  feet 
in  thickness  of  light-colored  crystalline  limestone,  characteristic  of  the  upper 
members  of  the  Madison  limestone.  The  upper  beds  are  highly  siliceous 
and  may  possibly  belong  to  the  Quadrant  quartzites,  although  no  such  heavy 
masses  of  siliceous  beds  were  recognized  as  to  warrant  a  reference  to  the 
overlying  formation.  An  anticline  in  the  limestone  crosses  Pacific  Creek 
in  a  northwest-southeast  direction,  the  beds  dipping  steeply  on  both  sides 
of  the  fold.     In  the  valley  the  limestone  lies  nearly  horizontal. 

According  to  Prof  J.  P.  Iddings,  both  the  Teton  and  the  Ellis  formations 
are  well  exposed,  overlying  the  Madison  limestone,  just  south  of  the  limits 
of  the  area  mapped.  The  red  beds  have  a  development  fully  600  feet  in 
thickness,  and  are  followed  by  a  gray  limestone  carrying  a  bed  of  white 
gypsum  5  feet  in  thickness.  Overlying  the  latter  comes  a  gray  fissile  lime- 
stone, followed  by  massive  beds  of  limestone  characterized  by  an  abmidance 
of  fossils.     From  these  beds  were  collected  the  following  species,  which 


MINK  CREEK.  199 

(lotinitoly  detcnnino  their  age  as  belonging  to  the  Ellis  formation:  Canifpto- 
ncctcs  platcsaifonnis,  C.  pertemiistriatus,  C.  bellistriatus,  Gyprina  iddingsi, 
Neritina  ivifoniingcnsis. 

Both  the  red  beds  of  the  Teton  and  the  limestones  and  sandstones  of 
the  Ellis  dip  steeply  down  the  mountain  sides,  and  are  exposed  along  Pacific 
Creek  below  the  mouth  of  Mink  Creek.  Here  they  are  abruptly  cut  off  by 
the  Snake  River  fault.  On  both  sides  of  Pacific  Creek  the  limestone  bluffs 
are  covered  by  the  basic  breccias. 

Mink  Creek. — Uudoubtcdly  tlic  Hglit-colored  limestones  exposed  by  the 
dee})  trench  cut  by  Mink  Creek  are  connected  with  those  of  Pacific  Creek, 
the  continuity  at  the  surface  being  broken  by  andesitic  breccias.  All  along 
Mink  Creek  the  abrupt  walls  of  light-colored  Madison  limestone  are  over- 
lain by  the  somber  breccias;  the  latter,  extending  to  the  top  of  the  plateau, 
afford  a  most  impressive  view.  On  the  divide  between  Fox  and  Mink 
creeks  the  limestone  is  well  shown  along  the  fault  just  southeast  of  the 
small  lake  indicated  on  the  map.  Lithologically  the  beds  resemble  the 
upper  members  of  the  Madison  limestone,  passing  into  coarse  crystalline 
beds  of  reddish  limestone,  characteristic  of  the  summit  of  the  formation. 
Near  the  top  of  the  ridge  the  limestones  yielded  well-preserved  specimens 
of  Spirifer  centronatus,  which  has,  however,  a  wide  geographical  distribution 
and  an  extended  vertical  range  throughout  the  Madison  limestone. 

Immediately  north  of  the  small  lake  just  mentioned  rises  a  bold  and 
isolated  hill  100  feet  in  height  and  one-half  mile  in  length,  in  striking 
contrast  to  the  surrounding  country.  It  is  formed  of  light-colored  pyroxene- 
andesite,  which  in  its  general  aspect  possesses  a  remarkable  resemblance  to 
rhyolite.  The  top  of  the  hill  is  smooth  and  polished  and  beautifully 
glaciated,  and  the  flat-topped  summit  is  marked  by  long  parallel  furrows 
frequently  20  inches  in  width  and  a  foot  deep,  the  result  of  ice  movement. 
In  the  cavities  of  the  porous  rock  Professor  Iddings  has  determined  the 
presence  of  tridymite. 

As  already  mentioned,  the  Madison  limestone  and  Teton  formation  are 
exposed  along  the  west  base  of  Two  Ocean  Plateau.  The  sedimentary 
rocks  come  to  the  surface  from  beneath  the  breccias  along  the  edge  of 
the  plateau  in  the  deeply  eroded  valley  of  Plateau  Falls.  Thence  they 
stretch  northward  in  an  unbroken  line  for  nearly  10  miles,  finally  dis- 
appearing beneatli  the  plateau  breccias  north  of  Grouse  Creek.     In  the 


200     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

lateral  valley  of  Plateau  Falls  the  upper  members  of  the  Madison  limestone 
are  well  developed,  exposing  a  thickness  of  nearly  400  feet  of  beds.  They 
have  yielded  Orthothetes  inflata,  found  throughout  the  Madison  limestone, 
and  Eudothyra  hailci/i  var.  waverJyensis,  as  yet  known  only  in  the  upper 
beds.  On  a  low  conical  hill  in  the  middle  of  the  valley  similar  limestones, 
canying  the  same  fossils,  occur  nearly  horizontal,  but  northward  they  dip 
to  the  east  and  north.  -They  pass  beneath  the  cherty  limestones  and  red 
beds  of  the  Teton  formation,  which  northward  are  also  exposed  along  the 
west  base  of  Two  Ocean  Plateau,  the  sunnnit  being  capped  by  breccias. 
Near  Crooked  Creek  the  Madison  limestone  again  comes  in,  inclined  south- 
ward, with  the  Teton  beds  apparently  lying  within  a  syncline  of  the 
Carboniferous  beds. 

Between  Crooked  and  Sickle  creeks  a  prominent  bold  bluff  of  lime- 
stone, facing  westward,  shows  several  hundred  feet  of  Madison,  which  still 
farther  north  passes  by  gradual  transition  into  siliceous  limestones  and 
quartzites.  According  to  Mr.  W.  H.  Weed,  the  latter  beds  belong  to  the 
overlying  Quadrant  quartzite.  This  long  strip  of  partially  exposed  sedi- 
mentary strata  indicates  much  folding  and  faulting-,  and  in  places  excessive 
compression  of  strata.  Geologically  it  is  of  mucli  interest,  as  it  is  probably 
a  remnant  of  an  old  mountain  range,  now  for  the  most  part  submerged 
beneath  a  vast  jDile  of  volcanic  ejectamenta,  which,  resting  upon  the  uneven 
surfaces  of  the  sedimentary  beds,  caps  their  highest  summits  and  stretches 
eastward  for  50  miles  across  Two  Ocean  Plateau  and  the  Absaroka  Rang-e. 
Bluish-gray  limestones  again  appear  from  beneath  the  breccias  upon  the 
east  side  of  the  Absaroka  Range,  in  a  higli  bluff  near  the  mouth  of  Stink- 
ingwater  Canyon,  carrying  Seminula  luimUis,  Spirifer  suhattenuatus,  Spirifer 
striatus  var.  madisonensis.  They  inark  the  limestone  as  being  a  part  of 
the  Madison  formation,  which  comes  out  from  beneath  the  breccias  on  both 
sides  of  the  volcanic  plateau. 

TWO   OCEAN  PliATEAU. 

Two  Ocean  Plateau  forms  the  most  western  outlier  of  the  massive  beds 
of  agglomerates  that  go  to  make  up  the  Absaroka  Range.  It  presents  an 
imposing  pile  of  volcanic  ejectamenta,  rising  10,000  feet  above  sea  level 
in  its  most  elevated  portions.  The  highest  portions  lie  to  the  eastward, 
with  a  gentle  dip  toward  the  submerged  range  which  rises  here  and  there 
above  the  plateau  along  the  east  side  of  the  Snake  fault.     The  plateau 


TWO  OOEAN  PLATEAU.  201 

stands  out  i'.s  a  pniniinent  and  sonu'wliat  isidated  physical  feature,  sepa- 
rated from  the  Ahsarokas  by  the  wide,  flat  valley  of  the  upper  Yellowstone, 
and  sharply  defined  on  the  north  by  the  broad  sheet  of  water  known  as 
Yellowstone  Lake.  The  continental  divide  crosses  the  summit  of  the 
plateau  with  a  northeast-southwest  course,  sending  its  waters  either  to  the 
Yellowstone  and  the  Atlantic  or  the  Snake  and  the  Pacific.  Owing  to  its 
broad  mass  and  great  elevation  the  snows  of  winter  accumulate  upon  it  to 
great  depths,  and  the  rains  of  summer  furnish  an  abundant  water  supply. 
Numerous  streams  leaving  the  plateau  have  trenched  deep,  narrow  lateral 
canyons  into  the  pile  of  breccias,  which,  with  steep  mural  faces,  drop 
abruptly  for  2,000  feet  to  Yellowstone  River. 

The  plateau  presents  a  comparatively  uniform  mass  of  basic  breccia 
throughout  its  entire  length,  from  Two  Ocean  Pass,  which  defines  its 
southern  limit,  northward  to  Yellowstone  Lake.  Andesitic  and  basaltic 
fragments,  more  or  less  firmly  compacted  together  by  fine  cementing  mate- 
rial, make  up  the  greater  part  of  the  mass.  Li  most  respects  it  is  quite  like 
the  basic  breccias  described  elsewhere  as  occurring  all  along  the  west  slopes 
of  the  Absarokas.  Exceptionally  fine  exposures  of  the  mass  are  shown  in  the 
abrupt  escarpments  along  the  upper  Yellowstone  all  the  way  from  Atlantic 
Creek  northward  to  Badger  Creek.  Seen  westward  across  Y^ellowstone 
Valley  these  walls  are  specially  impressive,  and  are  easily  studied  along 
the  cliffs  of  Falcon  and  Lynx  creeks.  Interbedded  in  the  breccias  are 
occasional  flows  of  compact  basalt,  lying  in  beds  one  above  another.  They 
usually  rest  upon  an  irregular,  uneven  surface  of  the  breccia,  and,  from 
evidences  of  weathering  observed  in  the  disintegrating  breccias,  indicate 
clearly  that  these  basalts  were  poured  out  over  a  surface  exposed  to  atmos- 
pheric agencies  for  a  long  period  of  time.  The  varying  thickness  of  the 
basalts,  their  thickening  and  thinning,  and  their  entire  absence  over  extended 
areas  prove  how  irregular  and  intermittent  were  the  overflows.  They  are 
by  no  means  so  thick  or  so  persistent  as  the  basalt  sheets  observed  in  the 
earlier  basic  breccias  in  the  main  portion  of  the  range.  The  heaviest 
developments  of  these  interbedded  flows  are  seen  in  the  southern  end 
of  the  plateau,  but  they  seldom  attain  a  thickness  of  100  feet,  and  in 
such  instances  are  made  up  of  a  series  of  individual  flows  not  always 
continuous. 

While  the  great  body  of  basic  breccia  consists  of  coarse  angular 
fragments,   with   here   and   there    basaltic    bowlders  measuring  2  feet  in 


202  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

diameter,  beds  composed  of  well-worn  and  rounded  material  are  frequently 
observed.  It  is  evident  that  this  latter  material  is  water-laid,  and  in  p-reat 
part  assorted  by  the  action  of  running  streams.  Much  of  this  matei'ial  is 
sandy,  consisting  of  volcanic  gravel  deposited  under  water.  It  is  also 
evident  that  all  this  material  is  volcanic  in  nature  and  derived  from  still 
higher  sources.  These  water-laid  beds  are  covered  by  flows  of  agglomerate 
and  coarse  unaltered  breccias  derived  from  explosive  action.  No  dikes 
were  observed  cutting  the  Two  Ocean  Plateau  breccias. 

The  mass  of  Two  Ocean  Plateau,  while  apparently  horizontal  as  seen 
almost  anywhere  from  a  distance,  has  a  gentle  inclination  to  the  north,  aver- 
aging, however,  not  more  than  3°.  It  seems  probable  that  the  entire 
plateau  has  suffered  from  a  slight  tilting  of  the  mass.  Evidence  of  such 
movement  may  be  seen  throughout  the  Absarokas.  It  would  seem  that 
the  flow  of  the  coarse  brecciated  mass  at  the  time  of  its  ejection  was  from 
the  eastward,  but  that  a  subsequent  orographic  movement  was  at  right 
angles  to  it,  the  mass  being  tilted  northward,  due  to  the  intrusion  of  masses 
of  granite-porphyry  to  the  southwest. 

The  east  and  west  sides  of  Two  Ocean  Plateau  are  sharply  contrasted 
in  the  lateral  trenches  which  cvit  the  plateau  body.  Along  the  Yellow- 
stone Valley  they  expose  masses  of  breccia  2,000  feet  in  thickness  without 
cutting  through  the  upper  basic  breccias,  while  on  the  west  side,  only  a  few 
miles  across,  the  walls  of  the  plateau  show  but  a  thin  covering  of  breccia, 
with  the  Paleozoic  and  Mesozoic  strata  lying  beneath  them.  The  border 
line  between  the  sedimentary  beds  and  the  breccias  follows  a  sinuous  course, 
with  tongues  of  breccia  penetrating  into  the  underlying  bodies.  One  of 
these  tongues  is  well  shown  near  the  junction  of  Mink  and  Pacific  creeks, 
where  a  fine  exposure  of  breccia  occurs  on  the  north  side  of  Pacific  Creek, 
while  higher  up  Mink  Creek  the  blue  limestones  of  the  Madison  formation 
stand  out,  capped  by  the  more  somber  breccias. 

Between  the  brecciated  mass  of  Two  Ocean  Plateau  and  that  lying  to 
the  westward  at  the  base  of  Mount  Hancock  and  along  Coulter  Creek,  there 
is  one  marked  difference  in  mode  of  occurrence.  The  former  shows  evi- 
dences of  material  having  been  transported  for  a  considerable  distance, 
while  at  the  latter  locality  there  is  every  indication  that  the  source  of 
material  thrown  out  was  near  its  present  position,  with  every  evidence  of 
explosive  action  along  a  line  of  profound  faulting  having  an  approximately 
north-south  trend. 


CHAPTER  A" I. 
GEOLOGY  OF  THE  SOUTHERN  END  OF  THE  SNOWY  RANGE. 


By  Walter  Harvey  Weed. 


GENERAL  DESCRIPTION. 

The  northeastern  part  of  the  Yellowstone  Park  embraces  a  small  por- 
tion of  the  great  range  of  mountains  which  extend  northward  to  the  low- 
lands of  the  Yellowstone  River,  a  chain  known  as  the  Snowy  Range. 
Within  the  limits  of  the  Park  only  the  extreme  southern  end  of  the  range 
occurs,  the  much  accidented  and  rugged  country  to  the  southeast  con- 
necting these  mountains  with  the  northern  part  of  the  eastern  mountain 
range  of  the  Park.  The  eroded  sedimentary  rocks  of  this  area  are  con- 
tinued beneath  the  great  accumulations  of  volcanic  materials  which  have 
been  heaped  up  to  form  the  Absaroka  Range. 

The  Snowy  Mountains  constitute  the  western  portion  of  a  high  moun- 
tainous tract  which  includes  the  great  peaks  of  the  Beartooth  Range,  the 
highest  mountains  of  Montana.  This  mountainous  area  is  terminated  on 
the  west  by  the  broad  mountain  valley  of  the  Yellowstone  River,  the 
region  being  divided  by  the  deep  valley  of  the  Bowlder  River  into  two 
parts,  of  which  the  westernmost,  between  the  Bowlder  and  Yellowstone 
valleys,  forms  the  Snowy  Range  proper.  The  general  structure  of  this 
entire  mountain  tract  is  that  of  a  broad  anticlinal  uplift,  the  central  portion 
of  which  has  been  denuded  of  its  former  covering  of  sedimentary  rocks 
and  variously  modified  by  faulting,  especially  at  the  soutliwestern  end,  near 
the  Yellowstone  Park.  The  greater  part  of  the  region  shows  the  core  of 
crystalline  schists,  gneisses,  and  granite  which  form  the  central  plateaus. 

The  central  portion  of  the  mountains  is  a  broad,  flat-topped  mass,  whose 
surface  constitutes  a  plateau  10,000  feet  above  sea  level,  deeply  cut  by 
canyons  3,000  to  4,000  feet  deep.     Above  this  plateau  the  peaks  rise  a 

203 


204  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

thousand  or  two  thousand  feet  higher.  The  plateau  is  glaciated,  and  ponds 
and  lakes  diversify  the  surface,  which  is  almost  completel}-  destitute  of  soil 
or  vegetation.  Along  the  southern  flanks  of  this  crystalline  axis  the  over- 
lying Paleozoic  strata  dip  away  from  the  central  mass  of  Archean  rocks. 

The  area  embraced  within  the  limits  of  the  Yellowstone  Park,  although 
but  a  small  part  of  the  range  itself,  includes  a  part  of  the  Archean  massif. 
The  schists  and  gneisses  are  deeply  ti-enched  by  streams  flowing  southward 
from  the  mountains  and  joining  the  Yellowstone  drainage  within  the  Park. 
Only  scattered  remnants  of  the  Paleozoic  rocks  which  formerly  covered 
the  crystalline  schists  are  now  found.  To  the  south  very  greatly  eroded 
sedimentary  masses  are  now  covei'ed  by  the  volcanic  breccias. 

TOPOGRAPHY. 

The  topography  of  that  portion  of  the  Snowy  Mountains  included 
within  the  mapped  area  presents  a  variety  of  configuration,  due  primarily 
to  the  nature  of  the  rock  masses.  For  the  purposes  of  the  present  dis- 
cussion the  southern  limit  of  the  range  may  be  regarded  as  defined  by  the 
Yellowstone  River,  its  eastern  fork,  Lamar  River,  and  the  eastern  branch 
of  the  latter  stream,  known  as  Soda  Butte  Creek.  Within  the  triangular  area 
thus  inclosed  we  have,  to  the  south,  the  sharp  volcanic  summits  of  Druid  and 
Bison  peaks  and  the  long,  narrow  crest  of  Baronet  Peak.  To  the  north  and 
west  broad,  gently  sloping  summits  extend  southward  and  break  abruptly 
in  steep  slopes  and  limestone  cliffs  to  the  valleys  of  the  streams  that  drain 
the  region.  The  principal  drainage  of  this  area  is  that  of  Slough  Creek 
and  its  tributar}-,  Buffalo  Creek.  The  former  stream,  heading  in  the  glacial 
amphitheaters  of  the  rugged  peak  known  as  Haystack  Mountain,  flows  in  a 
southwesterly  direction  through  a  wide  and  generally  open  valley  whose  sides 
expose  excellent  sections  qf  the  mountain-forming  rocks.  The  topographic 
peculiarities  of  the  stream  indicate  that  it  is  of  considerable  antiquity.  The 
present  vallev  bottom  is  deeply  filled  with  alluvium,  apparently  the  result 
of  the  damming  of  the  stream  in  glacial  times  and  the  formation  of  a  lake 
above  the  narrow  canyon  which  it  has  cut  through  Archean  gneisses  to  join 
Buff'alo  Creek.  The  latter  stream  has,  within  the  limits  of  the  area  mapped, 
cut  a  valley  in  Archean  gneisses,  the  gently  dipping  sedimentary  beds 
which  occur  upon  the  flat  plateau  summits  on  either  side  being  far  above 
its  present  channel. 


SOUTHERN  END  OF  THE  SNOWY  EANGE.  205 

The  valley  of  Lamar  River,  which  terminates  the  range  on  this  side, 
is  of  even  greater  anti(iuity,  and,  as  will  be  shown  in  Part  I,  it  was 
once  the  principal  drainage  of  this  entire  region.  Isolated  patches  of 
the  sedimentary  rocks  occnr  in  the  lower  part  of  the  valley,  where  denuda- 
tion has  removed  their  covering  of  volcanic  breccias.  Soda  Butte  Creek, 
which  has  been  assumed  to  represent  the  southeastern  boundary  of  the 
Snowy  Range,  presents  one  of  the  most  impressive  mountain  valleys  to  be 
found  within  the  limits  of  the  Park.  The  illustration  (PI.  XXVI)  of 
Baronet  Peak  shows  the  general  character  of  this  valley  and  the  rugged 
aspect  of  the  high  peaks  which  tower  above  it  on  either  side.  Farther  up 
the  stream,  at  the  confluence  of  Pebble  Creek,  the  sedimentary  rocks  occur 
in  the  valley  bottom.  Above  this,  in  the  upper  valley  near  the  mining 
settlement  of  Cook  City,  the  valley  walls  present  bold  limestone  cliffs,  over 
which  numerous  streams,  draining  the  higher  volcanic  slopes,  fall  in  a 
succession  of  cascades  that  are  of  great  beauty.  The  white  cliffs  of  sedi- 
mentary rocks  stand  out  in  bold  relief  from  the  somber  volcanic  slopes,  and 
their  steep  walls,  presenting  an-  unbroken  cliff  often  extending  for  miles 
along  the  sides  of  the  valley,  offer  few  opportunities  of  ascent. 

SEDIMENTARY  ROCKS. 

Any  attempt  to  describe  the  sedimentary  rocks  of  that  small  portion  of 
the  Snowy  Range  found  within  the  limits  of  the  Park  must  be  at  best  a 
fragmentary  sketch  of  the  Snowy  Range  itself.  Of  the  sedimentary  series, 
only  the  Paleozoic  rocks  occur  within  the  limits  of  this  area,  nor  do  these 
rocks  present  any  very  marked  differences  from  those  of  the  same  age 
occurring  in  the  other  ranges  of  the  region.  The  lowest  beds  exposed  are 
those  of  the  Flathead  formation.  Above  these  the  Grallatin  limestones, 
which  are,  within  this  region,  so  frequently  seen  in  long  lines  of  cliffs,  are 
well  exposed  and  cover  considerable  areas.  The  Silurian,  known  within 
this  region  as  the  Jefferson  formation,  presents  the  best  differentiation  of 
this  horizon  found  within  the  limits  of  the  Park.  Above  these  shallow- 
water  deposits  are  the  massive  limestones  and  thinly  bedded  shales  of  the 
Three  Forks  formation,  in  which  Devonian  fossils  have  been  found.  The 
highest  sedimentary  rocks  which  occur  within  this  region  are  those  of 
the  Madison  limestone. 


206  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  sedimentary  series  everywhere  presents  undoubted  evidence  of 
great  erosion  following  the  uplift  of  the  range,  antedating  the  extravasation 
of  the  volcanic  rocks  which  now  so  generally  mantle  it.  That  this  period 
of  denudation  was  long  is  indicated  by  the  profound  gorges  which  were 
cut  in  the  rocks  and  carved  deeply  into  the  underlying  schists.  The 
Mesozoic  beds,  if  present,  were  entirely  removed,  and  no  trace  of  them 
has  been  found  within  this  area  or  in  its  immediate  proximity.  It  is 
further  evidence  of  the  long  period  of  uplift  and  erosion  which  followed 
the  deposition  of  the  Laramie.^ 

The  following  table  presents  a  generalized  section  of  the  sedimentary 
formations  of  the  region. 

Snotpy  Mountain  section. 

Feet. 

I  Limestones,  carrying  fossils 150 

Madison (  Massive  beds  of  indurated  gray  limestones;  no  fossils 175 

_.         ,,     ,       (  Thinly  bedded  limestones:  characteristic  Devonian  fossils  from  lowest  beds 200 

Three  Forks.  <  •  .  ,  ,  .  o„ 

<  Purplish-colored,  thinly  bedded,  hssile  limestones,  carrying  gasteropod  remains..     20 

("Brown,  earthy-colored,  clayey  limestone  conglomerate 25 

J  Light  and  dark  gray,  thinly  bedded  limestones 150 

I  Crackled  white  limestones. 20 

[persistent  clift'-formiug  bed  of  massive  light-gray  limestone 200 

r Thinly  bedded  limestones,  carrying  fossils  at  base 100 

I  Thinly  bedded  limestones  and  limestone  conglomerate.     Fossils  from  summit  are 

^*"**'° I      Middle  Cambrian 250 

I  Dark-gray  mottled  limestones,  forming  persistent  cliff 100 

(-Black  limestones;  thinly  bedded,  carrying  fossils  (Middle  Cambrian) i 

I  Limestones  and  shales ) 

Flathead I  Thinly  bedded  limestones 200 

I  Shales 200 

^  Sandstone  and  quartzite 100 

Archean Gneiss  and  schist. 

BUFFALO  PLATEAU. 

This  flat-topped  mountain  tract,  lying  between  Hellroaring  and  Buffalo 
creeks,  together  with  adjacent  areas  across  these  streams,  constitutes  the 
true  southern  termination  of  the  Snowy  Range.  The  plateau  is  of  gneiss, 
on  which  remnants  of  sedimentary  rocks  now  form  the  highest  points.  The 
gneiss  presents  considerable  variety,  but  consists  usually  of  feldspathic 
forms,  and  shows  a  well-defined  lamination  toward  the  east.  The  surface 
is  glaciated,  smooth  ice-worn  bosses  and  striated  surfaces  being  common, 

'The  Laramie  and  the  overlying  Livingston  formation  in  Montana,  by  W.  H.  Weed:  Bull.  U.  S. 
Geol.  Survey  No.  105,  Washington,  1893. 


BUFFALO  PLATEAU.  207 

while  the  southwestern  skipes  are  hirgely  covered  by  moraiual  drift. 
Within  the  hniits  of  the  I'ark  the  j^neiss  forms  the  west  side  of  the  phiteau 
to  within  100  feet  of  the  top,  where  it  is  overlain  by  a  horizontal  bed  of 
indurated  sandstone,  which  is  undoubtedly  the  basal  bed  of  the  Flathead 
formation.  The  rock  is  mottled  with  red  and  white  streaks  and  layers,  and 
resembles  the  beds  exposed  on  the  southwestern  flank  of  Bison  Peak. 
The  exposure  is  100  feet  thick,  50  feet  of  which  is  vertical  cliff.  The  top 
of  the  plateau  is  generally  covered  with  a  growth  of  pine,  but  where  the 
sandstone  prevails  the  surface  is  open  and  grassy  and  in  strong  contrast 
to  the  gneissic  areas.  The  summit  of  the  plateau  rises  gradually  to  the 
east  to  a  high  ridge,  trending  north.  About  100  feet  above  the  quartzite  a 
thinly  bedded  mottled  limestone  occurs,  the  rocks  being  horizontal.  This 
rock  closely  resembles  the  limestones  found  in  the  valley  of  Soda  Butte 
and  Slough  creeks.  The  high  point  (9,100  feet)  on  this  plateau,  which 
lies  just  within  the  Park  line,  is  formed  of  massive  limestone  that  weathers 
with  a  very  rough  surface  and  shows  a  few  fossils  which  prove  that  the 
beds  belong  to  the  Three  Forks  formation.  Two  hundred  feet  below 
this  summit  a  massive-bedded,  coarsely  mottled,  dark-gray  limestone 
occurs,  the  strata  forming  the  base  of  the  Gallatin  limestone  and  having  a 
dip  of  3°  E.  These  two  prominent  beds  of  massive  limestone  are  readily 
recognizable  horizons,  which  are  as  prominent  in  the  Snowy  Range  as 
they  are  in  the  Gallatin  Mountains.  The  extreme  erosion  of  the  old  land 
surface  before  the  deposition  of  the  volcanic  breccias  and  the  Cambrian 
rocks  is  well  illustrated  in  this  area.  Basic  breccias  rest  upon  the  various 
beds  just  noted  and  also  upon  the  gneiss,  and  in  the  valleys  and  lower 
slopes  at  the  south  end  of  Buffalo  Plateau  the  volcanic  rocks  fill  hollows  in 
the  greatly  eroded  surface. 

IiAMAR  VALLiEY. 

The  valley  of  Lamar  River,  which  appears  to  be  one  of  the  most  ancient 
drainage  ways  of  the  Park,  is  cut  through  a  variety  of  rocks,  most  of  which 
are  volcanic.  The  gneissic  rocks  are  exposed  on  the  south  flanks  of  Speci- 
men Ridge  and  are  cut  through  by  the  river  and  by  its  tributary,  Slough 
Creek.  On  the  west  the  gneiss  forms  rough  and  rugged  slopes,  but  near 
Crystal  Creek  the  rounded  bosses  of  the  summit  slope  gently  to  the 
southeast  and  pass  beneath  the  adjacent  rocks.     On  the  south  side  of  Lamar 


208  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

River  the  gneiss  is  overlain  by  a  remnant  of  the  limestones  that  once  cov- 
ered it.  The  rock  sequence  of  Cambrian  and  higher  rocks  has  not  been 
recognized,  and  it  is  probable  that  a  fault  exists  between  the  exjjosures  of 
the  gneiss  and  of  the  limestone,  for  the  latter  carries  poorly  preserved  fossils 
of  Carboniferous  types,  the  beds  dipping  gently  to  the  southeast  at  5°  and 
forming  low  rounded  knolls  near  the  wagon  road.  Tliese  limestones  are 
somewhat  crystalline,  have  but  indistinct  bedding,  and  differ  quite  materi- 
ally from  the  Paleozoic  strata  seen  elsewhere  in  the  vicinity.  A  thickness 
of  between  200  and  300  feet  is  exposed  in  an  area  whose  boundaries  can 
not  be  closely  defined  owing  to  the  ovei'lapping  rhyolite  sheet  and  the  pre- 
vailing mantle  of  drift,  but  the  sedimentarj^  rocks  certainly  cover  the  high 
ground  east  of  the  wagon  road. 

North  of  Lamar  River  the  western  slopes  of  Bison  Peak  show  well- 
bedded,  dark-colored  basic  volcanic  breccias,  separated  from  the  gneissic 
hill  lying  between  Slough  Creek  and  Lamar  River  by  a  well-marked  depres- 
sion v'hich  defines  the  boundary  line  between  the  two  rocks.  The  gneiss 
is  overlain  at  the  highest  point  on  this  boundary  line  by  a  bed  of  quartzite, 
which  is  of  the  usual  pink  and  white  variety,  dipping  5°  S.,  the  strike 
being  N.  12°  W.  This  quartzite  makes  a  cliff  25  to  40  feet  high,  that 
rises  abruptly  above  the  lakelet  found  upon  the  divide.  The  rock  is  gen- 
erally somewhat  fissile,  well  bedded,  and  of  the  normal  character  of  the 
Flathead  quartzite. 

SLOUGH   CREEK. 

The  valley  of  Slough  Creek  above  the  confluence  of  Buffalo  Creek 
presents  the  picturesque  scenery  characteristic  of  this  part  of  the  Snowy 
Range.  The  broad  meadow  lands  which  cover  the  valley  bottom  are  flanked 
by  gentle  slopes,  with  scattered  groves  of  aspen  and  pine,  above  which  are 
the  bold  cliffs  of  white  limestone  that  separate  the  lower  slopes  from  the 
crags  of  somber-colored  breccias  which  form  the  upj^er  part  and  summit  of 
the  mountains.  This  valley  presents  the  best  exposures  of  the  lower  Paleo- 
zoic series  to  be  found  in  this  part  of  the  Park,  and  the  general  section  of 
the  sedimentary  rocks  of  the  range  which  has  just  been  given  is  compiled 
from  observations  made  in  this  valley  and  in  the  cliffs  of  the  neighboring 
valley  of  Soda  Butte  Ci'eek. 

Li  the  lower  end  of  Slough  Creek  Valley  the  slopes  on  either  side 


SLOUGH  CREEK.  209 

])resent  sharply  ('ontriistin<j'  goological  coiulitions.  On  the  north  Aroheiin 
gneisses  prevail,  and  tlie  sedimentary  rocks  which  are  })resent  farther  up 
the  vaUe}'  are  here  entirel}'  absent.  The  gneisses  form  bold  but  smooth 
and  glaciated  exposures,  extending  down  to  the  valley  floor  and  showing 
in  abrupt  hillocks  and  knolls,  rising  like  islands  above  the  meadows.  The 
Archean  rocks  present  evidence  of  glaciation  whose  movement  was  from 
the  northeast,  and  the  present  toj)ography  is  eminently  glaciated.  On  the 
opposite  side  of  the  valley  the  sedimentary  rocks  outcrop  along  the  foot 
slopes  of  Bison  Peak  and  extend  continuously  along  the  valley  Avail  to  the 
Park  boundary.  The  thinly  bedded  shales  and  limestones  of  the  Flathead 
series  form  gentle  slopes,  whose  covering  of  soil  and  vegetation  generally 
obscures  the  rocks.  The  Flathead  quartzite  is  not  seen  here,  the  bed  being 
completely  concealed  beneath  the  alluvial  bottom  land. 

The  lower  slopes  of  Bison  Peak  below  Plateau  Creek  show  ledges  of 
a  mottled,  heavy-bedded,  massive  limestone  exposed  in  cliffs  75  to  100 
feet  high,  the  summits  of  the  beds  forming  flat-topped  benches  sloping 
gently  to  the  south.  North  of  Plateau  Creek  the  limestones  extend  down 
to  the  valley  bottom,  and. are  well  exposed  on  the  slopes  to  the  east,  bench 
upon  bench  of  limestone  showing  on  the  slopes,  with  continuous  bluffs 
which  are  extremely  difficult  to  cross  in  ascending  the  mountain.  The  beds 
have  a  strike  of  N.  60°  E.  and  dip  5°  S.,  the  highest  ledges  exposed  being 
found  at  an  elevation  of  6,400  feet,  where  the  breccias  rest  ujDon  them. 
These  limestones  were  traced  along  the  mountain  flanks  as  far  north  as 
Elk  Tongue  Creek.  This  stream  has  cut  along  the  contact  between  the 
breccias  and  the  limestones,  and  the  exposure  gives  additional  evidence 
of  the  rugged  nature  of  the  country  at  the  time  the  volcanic  breccias  were 
laid  down.  The  lower  rocks  exposed  are  thinly  bedded  limestones  carrying 
Middle  Cambrian  fossils,  and  the  rocks  are  covered  by  groves  of  aspen  and 
gi'assy  slopes  whose  character  is  readily  recognized  as  differing  from  that 
of  the  breccia  slopes  above  them. 

The  most  conspicuous  exposures  of  the  sedimentary  rocks  are  those  on 
the  northern  side  of  this  valley,  near  its  upper  end,  where  the  limestones 
form  cliffs  which  extend  along  the  valley  slopes  for  many  miles  to  the 
northward.  The  lowest  exposures  are  thinly  bedded  limestones,  liglit  gray 
in  color,  with  yellowish  mottlings,  and  lithologically  similar  to  the  Flat- 
head limestones  seen  elsewhere.     These  strata  make  steep  slopes  which  are 

MON   XXXII,  PT    II li 


210  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

terraced,  the  floor  of  each  bench  being-  the  bedding  plane  of  the  stratum 
below.  These  limestones  are  capped  by  a  thick  bed  that  is  the  mottled 
limestone  forming  the  base  of  the  Gallatin  formation.  This  bed  is  about 
200  feet  thick,  and  froni  the  meadow  lands  of  the  valley  it  can  be  seen 
as  a  persistent  clift'  that  is  a  readily  recognizable  horizon,  and  forms  an 
almost  impassable  barrier  in  the  ascent  of  the  slopes.  It  is  overlain  by  less 
massive  limestones,  capped  Ijy  basic  volcanic  breccias.  The  irregularit}' 
of  the  surface  upon  wliich  these  breccias  were  deposited  is  beautifully 
illustrated  by  the  exposures  seen  in  this  escarpment.  The  face  of  the  cliff 
shows  the  massive  bed  of  mottled  limestone,  with  a  deep  indentation  that  is 
cleai'ly  a  cross  section  of  an  old  drainage  way  filled  by  volcanic  breccias 
which  are  now  firmly  indurated.  The  top  of  the  mottled  limestone  bed 
forms  a  bi'oad  and  distinctive  bench  which  extends  along  the  slopes.  Above 
this  bench  the  thinly  bedded  limestones  are  seldom  seen,  and  though  the 
slopes  are  terraced  and  are  open  and  grass  covered,  no  good  exposures  are 
found,  owiuff  to  the  abundance  of  rounded  andesitic  drift  from  reasserted 
breccia  beds  which  cover  the  summit  of  the  plateau. 

At  the  upper  end  of  the  Slough  Creek  Valley  the  mountains  close  in 
and  the  stream  flows  through  a  gorge  cut  in  Archean  gneiss  and  massive 
igneous  rocks.  At  one  point  the  stream  forms  a  pictui-esque  waterfall  in 
which  the  water,  cutting  along  joint  planes  of  the  rock,  is  separated  into 
two  cascades,  given  the  name  of  Twin  Falls.  Above  this  canyon  is  the 
upper  mountain  valley  of  Slough  Creek,  whose  bottom  is  a  labyrinth  of 
beaver  ponds,  sluggish  channels,  and  willow  groves,  making  the  name  of 
the  stream  most  appropriate.  West  of  the  valley  the  same  sedimentary 
formations  noted  are  seen  in  terraced  slopes,  above  which  the  persistent  cliff 
of  mottled  limestone  is  again  present,  extending  northward  to  the  forking 
of  the  creek,  where  gneisses  and  volcanic  breccia  replace  the  sedimentary 
rocks.  The  eastern  side  of  this  upper  valley  of  Slough  Creek  shows  no 
sedimentary  rocks,  the  dark,  heavily  timbered  slopes  rising  to  sharp  craggy 
summits  of  volcanic  breccias. 

SODA  BUTTE   CREEK. 

Carboniferous  limestones  are  found  at  the  southeastern  base  of  Druid 
Peak,  and  form  the  valley  floor  about  the  hot-spring  cone  which  has  given 
Soda  Butte  Creek  its  name.     The  rocks  are  horizontal  or  but  genth'  tilted 


PEBBLE  CREEK.  211 

and  b(.'lt)n<!;  to  tlio  Madison  formation.  On  the  nortli  bank  of  Lamar  River, 
near  the  mouth  of  So(hi  Butte  Creek,  there  is  an  exposure  of  50  feet  of 
limestone.  The  beds  are  horizontal,  from  2  to  4  feet  thick,  and  possess  a 
peculiarly  rou<>h,  weathered  surface,  but  so  far  as  observed  do  not  carry 
fossils  and  are  not  cherty.  Another  exposure  nearer  Soda  Butte  Creek  is 
found  200  feet  above  the  river,  tlie  most  prominent  ledge  being  a  fissile 
limestone  20  feet  thick,  carrying  variegated  chert  and  Carboniferous  fossils. 
These  beds  dip  west  of  south  at  10°.  These  limestones  forn\  tlie  low  flat- 
topped  knolls  which  are  so  distinct  a  topographic  feature  of  the  southeast 
base  of  Druid  Peak,  as  they  are  quite  unlike  the  topography  prevailing  in 
the  breccia  areas.  On  the  shores  of  the  small  lakelet  which  a  landslide  of 
breccia  has  formed  on  the  lower  slopes  of  the  peak  the  beds  are  tilted, 
dipping  west  at  55°  and  striking  north  and  south,  but  it  is  probable  that 
they  have  been  dislocated  by  a  landslide. 

PEBBLE   CREEK. 

Light-gray,  massively  bedded  limestones  are  exposed  at  the  mouth  of 
Pebble  Creek,  forming  a  rounded  knoll  on  the  south  side  of  the  stream. 
The  rocks  contain  rather  scanty  fossil  remains,  which  prove  that  the  beds 
belong  to  the  Madison  formation.  These  beds  also  outcrop  along  the  north 
base  of  Abiathar  Peak,  1,300  feet  above  the  creek  bottom.  Pebble  Creek 
has  cut  a  narrow  gorge  through  the  limestone,  whose  beds  form  vertical 
walls  100  feet  high.  The  strata  are  nearly  horizontal  and  are  exposed  for 
300  feet  above  the  channel  of  Soda  Butte  Creek.  Above  the  mouth  of  the 
stream  the  valley  of  Pebble  Creek  shows  heavily  wooded  slopes,  with  no 
exposures  until,  near  its  head,  limestone  again  appears,  being  exposed  on 
both  sides  of  the  valley  beneath  a  capping  of  andesitic  breccias,  as  shown 
in  the  accompanying  plate  (PI.  XXVI).  Above  the  creek  on  the  spur  just 
outside  of  the  Park  boundary  occurs  a  thickness  of  800  feet  of  limestones,  the 
beds  dipping  at  a  low  angle  to  the  southwest.  The  west  base  of  Baronet 
Peak  and  the  ridge  of  which  it  is  the  highest  point  show  limestones  dipping 
from  1°  to  5°  S.  On  the  south  side  of  Pebble  Creek,  just  north  of  the 
limits  of  the  area  mapped,  but  within  the  Park,  about  100  feet  lower  than  the 
low  saddle  that  indents  the  ridge,  occurs  a  mottled  Cambrian  limestone 
carrying  fragments  of  trilobites,  the  rocks  being  nearly  horizontal. 


212  GEOLOGY  OF  THE  YELLOWSTONE  NATIOISTAL  PARK. 

SODA  BUTTE   VAL,I.EY. 

For  some  distance  above  the  mouth  of  Amphitheatre  Creek  the  valley 
of  Soda  Butte  is  narrow,  the  stream  flowing  through  a  gorge  cut  in  volcanic 
rocks.  Its  upper  course  is,  however,  through  a  broad  valley,  with  flat 
gravelly  bottom  and  with  striking  cliff's  of  limestone  appearing  on  either  side. 
The  limestones  exposed  at  the  mouth  of  Pebble  Creek  extend  up  the  western 
side  of  the  Soda  Butte  Valley  to  near  the  mouth  of  Amphitheatre  Creek. 
As  no  exposures  appear  on  the  east  side  of  Soda  Bvitte  Creek,  it  is  evident 
that  the  sedimentary  rocks  were  cut  away  before  the  deposition  of  the 
volcanic  breccias. 

An  examination  was  also  made  of  the  rocks  exposed  on  the  south 
slopes  of  the  high  limestone  mountain  that  is  capped  b}"  breccia  and  lies 
north  of  Soda  Butte  Creek.  The  lower  slopes  of  this  peak  are  covered 
with  large  blocks  of  limestone,  the  talus  from  the  cliffs  above.  The  lowest 
exposures  are  of  strongly  mottled  dark-colored  limestones,  overlain  by 
limestone  conglomerates,  with  light-gray,  chert-bearing,  massive-bedded 
limestones  above.  These  rocks  show  an  old  surface  that  is  quite  irregular. 
The  andesite  rests  upon  a  cemented  mass  of  large  blocks  and  fragments  of 
limestone.  The  heavy  limestone  belt  of  Soda  Butte  Creek  above  this  point 
is  exposed  some  500  feet  above  the  stream,  the  rocks  being  nearly  horizontal. 

The  following  sections,  made  by  Professor  Iddings,  show  the  sequence 
and  character  of  the  sedimentary  rocks  exposed  in  this  vicinity: 

Section  of  beds  on  north  si  fie  of  Soda  Butte  Creek. 

Feet. 

{Gray  limestones,  carrying  fossils  and  chert 10 
White  limestones,  much  crackled  and  biecciated 20 
Massively  bedded,  light-gray  limestones,  forming  cliff 200 

f  No  exposure 50 

Thinly  hedded  limestones,  carrying  trilobites 50 

Thinly  bedded  limestones  and  limestone  conglomerates,  carrying  abundant  fossils 
near  top.     The  limestones  are  glauoonitic,  thinly  bedded,  and  weather  with  a 

yellowish  surface,  often  studded  with  fossils  in  relief 190 

Tallatin  Thinly   bedded    limestones    and  much    limestone   conglomerate.      The  rock  is  a 

dense  light-gray  limestone,  and  the  conglomerate  is  formed  of  flat  and  very  thiu 
beach  pebbles,  and  the  rocks  carry  trilobites  and  .i  few  shell  remains  at  summit 
of  exposure.     The  conglomerate  is  intraformational;  that  is,  the  pebbles  , are  of 

the  same  limestones 60 

Mottled  dark-colored  limestone,  forming  a  massive  bed  that  is  generally  a  cliff 

100  feet  in  height 100 

r  Trilobite  remains  occur  in  a  black  limestone  that  is  oolitic,  full  of  dark  glauconitic 

Flathead J      grains,  and  is  quite  characteristic  for  this  horizon.     The  thickness  of  limestone 

probably  does  not  exceed  100  feet.     It  is  underlain  by  soft  laminated  shales 400 


SODA  BUTTE  VALLEY.  213 

The  forefroinar  section  was  observed  on  tlie  north  side  of  Soda  Butte 
Creek,  near  the  forty-fifth  meridian,  the  locaht}'  being-  a  mile  west  of  tliat 
just  noted.  Mottled  limestones  form  the  lowest  strata  exposed,  occurring- 
100  feet  above  an  exposure  of  (juartz-porphyry.  The  lowest  bed  is  a  fissile, 
dark-colored  limestone,  carrying  numerous  fragments  of  trilobites  and  over- 
lain by  a  massive,  dark-colored,  mottled  limestone,  which  is  the  base  of  the 
Gallatin  formation,  and  which  hei'e  forms  a  cliff  fully  100  feet  high.  This 
is  the  lowest  horizon  seen  on  the  north  side  of  the  creek,  but  on  the  south 
there  are  patclies  of  sliale  which  belong  to  the  Flathead  formation.  Above 
the  dark,  coarsely  mottled  limestone  cliffs  are  more  thinly  bedded,  gray 
limestones  and  limestone  conglomerates.  Fossils  collected  from  this  hori- 
zon are  of  Cambrian  age  and  were  obtained  60  feet  above  the  top  of  the 
cliff".  At  1,050  feet  above  the  stream  similar  limestones  form  projecting 
ledges,  and  the  rock  carries  many  trilobite  spines  and  a  few  fossils.  The 
rocks  50  feet  higher  up  are  similar  and  carry  similar  fossils  and  a  few  cri- 
noid  stems,  which  in  this  region  are  not  commonly  found  at  this  horizon. 
A  heavy  belt  of  light-gray  limestone,  weathering  with  a  rough  surface  and 
showing  no  fossils  except  crinoid  stems,  and  representing,  it  is  believed,  the 
JeflFerson  formation,  occurs  at  1,150  feet  above  the  stream.  This  belt  is 
about  200  feet  thick  and  is  overlain  by  a  white,  much  brecciated  limestone 
about  20  feet  thick,  overlain  in  turn  by  gray  limestones  5  to  10  feet  thick, 
carrying  traces  of  fossils  and  some  chert.  These  limestone  beds  are  nearly 
horizontal,  although  at  the  west  end  of  the  low  saddle  between  Pebble 
Creek  and  the  Soda  Butte  Valley  they  dip  30°  SW.  This  sudden  change 
in  dip  is  probably  due  to  intrusive  quartz-porphyry  that  may  form  a 
laccolithic  mass  under  the  horizontal  beds  that  occur  at  the  highest  point. 
Section  of  beds  at  north  base  o/Abiathar  Peak. 

Feet. 

i'  Andesitic  breccia,  forming  summit  of  mountain. 
Limestones,  carrying  Carboniferous  fossils 150 
Massive  belt  of  indurated,  gray  limestone  in  which  no  fossils  were  found 175 

I  Beds  generally  covered  by  talus  from  the  clift'  above.  At  the  base  the  ledges  are 
fossiliferous  and  carry  au  abundance  of  shell  remains,  which  are  of  Devonian 
types.  The  rock  is  a  tine-grained  buff  or  yellow  limestone,  varying  to  abrowu- 
gray  limestone,  very  finely  crystalline  and  carrying  an  abundance  of  finely  stri- 

I      atedshells 200 

(^Purplish  and  red  limestones,  thinly  bedded  and  c.irrylng  gastropod  remains 20 

C  Brown,  earthy,  and  argillaceous  limestone  conglomerates -. , 

I  Light  and  dark  colored,  thinly  bedded  limestones \   200 

1  Crackled  white  limestones ' 

l Massive  bed  of  light-colored  limestone,  forming  peisistent  cliff 200 


Three  Forks. 


214  GEOLOGY  OF  THE  YELLOWSTONE  l^ATIONAL  PAEK. 

{Limestone  conglomerates  and  thinly  bedded  limestones,  with  trilohite  remains..  ■. 
Massive  belt  of  dark-green  mottled  limestone,  resembling  the  same  formation  >    850 
in  the  Gallatin  Range ' 

Flathead Shales. 

This  section  was  made  on  the  high  limestone  bluff  at  the  north 
base  of  the  north  spur  of  Abiathar  Peak.  At  the  northwest  base  of  the 
spur  the  strata  dip  to  the  southwest.  The  dark-colored,  coarsely  mottled 
limestone  belt  which  is  the  base  of  the  Grallatin  formation  is  again  exposed, 
overlain  by  finely  bedded  limestones  bearing  trilobites  and  by  limestone 
cono-lomerates.  Higher  up  the  slope  the  massive  belt  of  light-colored 
limestone  belonging  to  the  Jefferson  formation  Aveathers  in  an  almost 
insurmountable  cliil'  extending  along  the  valley  wall  for  a  long  distance. 
The  top  of  this  bed  is  about  1,000  feet  above  the  creek.  It  is  overlain  by 
a  stratum  of  broken  limestones,  followed  by  light  and  dark  limestone  beds 
without  noticeable  fossils  up  to  200  feet  above  the  gray  belt.  At  this  point 
a  purplish  layer  carrying  gastropods  overlies  a  brown  earthy  and  clayey 
layer  of  limestone  conglomerate  with  a  fossiliferous  ledge  20  feet  above. 
Fossils  collected  from  these  beds  show  that  it  belongs  to  the  Three  Forks 
formation.  The  talus  slope  for  200  feet  above  these  Devonian  strata  shows 
no  exposures  until  we  reach  the  base  of  a  massive  limestone  about  1,500 
feet  above  the  cliff  of  Jefferson  limestone.  The  limestones  composing  this 
upper  belt  are  indurated  and  not  fossiliferous,  but  the  strata  exposed  above 
it,  at  1,675  feet  above  the  stream,  contain  numerous  fossils.  The  limestones 
extend  150  feet  higher,  where  the  eroded  surface  is  overlain  by  dark-colored 
basic  breccias. 

The  limestone  bluffs  extend  along  both  sides  of  the  Soda  Butte  Valley 
to  Cook  City  and  continue  up  RepubHc  Creek  for  2  miles.  CrystaUine 
schists  are  exposed  on  the  road  100  feet  above  the  Republic  Creek  road, 
and  also  on  the  lower  slopes  of  Mount  Henderson,  the  gneiss  forming 
obscure  outcrops.  The  Flathead  shales  are  exposed  higher  up  the  slopes, 
at  700  feet  above  the  stream  bottom.  Above  them  the  dark-colored  and 
mottled  Gallatin  limestone  is  exposed,  but  the  rock  is  much  altered  and 
mineralized.  Still  higher  on  the  south  slope  of  Mount  Henderson,  east  of 
the  road,  are  altered  shales  and  limestones  with  hornblende-mica-andesite- 
porphyry  well  exposed.  The  summit  of  Mount  Henderson  consists  of 
heavily  bedded  mottled  limestone,  broken  through  by  intrusive  rock,  which 
cuts  across  the  bedding  and  also  forms  intrusive  sheets. 


CHAPTER     VIT. 
THE  DISSECTED  VOLCANO  OF  CRANDALL  BASIN,  WYOMING. 


By  Joseph  Paxson  Iddings. 


INTRODUCTION. 

The  exploration  of  the  country  in  the  northeastern  corner  of  the  Yel- 
lowstone Park  and  immediately  east  of  it  led  to  the  discoveiy  of  a  volcano 
so  eroded  as  to  expose  its  internal  structure  and  to  permit  the  connection  or 
relationship  between  coarsely  crystalline  and  glassy  forms  of  the  same 
mag-mas  to  be  distinctly  made  out.^  More  or  less  satisfactory  demonstra- 
tions of  this  relationship  have  been  made  at  different  times  within  the  last 
twenty-five  years,  but  few  of  them  have  been  based  on  occurrences  where 
the  evidences  of  the  former  existence  of  a  typical  volcanic  cone  have  been 
unquestionable. 

The  classic  studies  on  "The  secondary  rocks  of  Scotland,"^  by  Prof. 
John  W.  Judd,  and  his  memoir  "On  the  ancient  volcano  of  Schemnitz, 
Hungary,"^  describing  the  "basal  wrecks"  of  Tertiary  volcanoes  in  these 
regions,  while  accepted  by  many  as  conclusively  demonstrating  the  con- 
temporaneity of  the  granular  rocks  and  volcanic  lavas  at  these  localities, 
failed  to  convince  a  large  number,  who  imagined  that  the  observations 
might  be  susceptible  of  othev  interpretations. 

The  dissected  volcano  of  Tahiti,  visited  in  1839  by  James  D.Dana,*  was 
considered  by  him  to  have  been  sufficiently  eroded  to  disclose  a  granular 
core,  but  there  was  no  opportunity  offered  at  the  time  of  his  visit  to  exjjlore 

'  Jour.  Geol.,  Vol.  1, 1893,  p.  606. 

^  Quart.  Jour.  Geol.  Soc.  Loudon,  Vol.  XXX,  1874,  pp.  2l'0-302. 
'  Idem,  Vol.  XXXII,  1876,  p.  293. 

<Unit«d  States  Exploring  Expedition  during  the  years  1838,  1839,  1840,  1841,  1842,  under  the 
command  ofCharles  Wilkes,  U.  S.  N.,  Vol.  X,  Geology,  by  James  D.  Dana,  Philadelphia,  1849. 

215 


216  GEOLOGY  OF  THE  YELLOWSTOKE  NATIONAL  PARK. 

the  mountain  thorouglil)'^  The  coarsely  crystalline  bodies  of  rock  noticed 
by  Charles  Darwin  in  the  Andes,  and  found  by  Prof.  A.  Stelzner  in  the 
andesite  lavas  of  Argentina,  lack  satisfactory  description. 

The  volcanic  center  at  Electric  Peak  and  Sepulchre  Mountain,  in  the 
Yellowstone  National  Park,  described  in  a  previous  chapter,-  furnishes 
indisputable  evidence  of  the  relationship  in  question  and  of  its  former 
existence  as  the  center  of  a  volcano.  However,  the  geological  structure  of 
this  locality  does  not  meet  our  expectations  of  what  a  great  volcano  should 
look  like  when  deeply  eroded.  In  fact,  profound  faulting  and  extensive 
erosion  have  left  very  little  of  the  original  volcanic  pile. 

But  no  simpler  or  more  obvious  model  of  the  internal  arrangement  of 
a  great  volcano  could  be  wished  for  than  that  which  is  exhibited  by  the 
deeply  cut  valleys  and  steep,  high  ridges  that  constitute  the  drainage  basin 
of  Crandall  Creek  and  its  immediate  vicinit)^  The  coarsely  crystalline 
gabbros  and  diorites,  with  smaller  bodies  of  granite,  exposed  for  a  height  of 
3,000  feet,  are  plainl}^  seen  to  have  been  intruded  within  a  vast  accumulation 
of  basaltic  tuff  and  scoriaceous  breccia,  which  they  have  metamorphosed. 
From  this  coarsely  cr^^stalline  mass  as  center,  dikes  of  fine-grained  rock 
penetrate  the  surrounding  lavas  in  all  directions,  the  dike  rocks  becoming 
finer  grained  rapidl}'  as  they  leave  the  once  heated  core.  They  form  a  net- 
■vvork  of  branches  which  connect  the  outlying  aphanitic  and  characteristically 
volcanic  rock?  with  the  more  crystalline  dikes  near  the  core,  which  finally 
merge  into  the  granular  body  of  the  gabbro  and  diorite.  The  whole  com- 
plex is  so  intimately  interwoven  that  there  is  not  only  no  possible  doubt  as 
to  the  relative  time  of  eruption  of  the  glassy  basaltic  scoria  and  lavas  and 
of  the  gabbro  and  diorite,  but  there  appears  to  be  no  ground  for  designating 
a  part  only  of  the  rocks  involved  in  the  complex  as  volcanic. 

GEOLOGICAL  DESCRIPTION. 

GENERAL  FEATURES. 

The  tract  of  country  embraced  in  the  description  of  the  volcano  of 
Crandall  Basin  lies  immediately  east  of  the  northeastern  corner  of  the 
Yellowstone  Park,  and  includes  an  area  somewhat  larger  than  that  drained 


'  Also,  A  dissected  volcanic  mountain;  some  of  its  revelations:  Am.  Jour.  Sci.,  Sd  oeries,  Vol. 
XXXH,  No.  190,  Oct.,  1886. 

-  Page  89.  See  also  The  mineral  composition  and  geological  occurrence  of  certain  igneous  rocks 
in  the  Yellowstone  National  Park :  Bull.  Philos.  Soc.  Washington,  Vol.  XI,  pp.  191-220 ;  and  The  eruptive 
rocks  of  Electric  Peak  and  Sepulchre  Mountain,  Yellowstone  National  Park :  Twelfth  Ann.  Rept.  U.  S. 
Geol.  Survey,  Part  1, 1891,  pp.  .569-664. 


27 


U  S  GEOLOGICAL  SURVEY 


MONOGRAPH  XXXII.PAHTII.PL  XXVn. 


LEGEND 


Phs 


H.it  Svl■iIl^iB 
lonuHti(in 


>  PLEISTOCENE 


Cim^Mierale 


Cm  i>  CARBONIFEROUS 


~Sj       I      j>  SILURIAN 


H 


€f 


>  CAMBRIAN 


Ibrjiiation. 


n\\./ 


Ngd, 


Gabhro  diiirite 
iiilrusivii  rocks . 


Nrh 


Nlab 


Lale  acid- 
breccia. 


Nebl 


Nbst 


Nebb 


Earty  basic 
breccia. 


Eeab 


"]>  EOCENE 


Earb'  acid 
breccia. 


/Bgn    I  y  ARCHEAN 


Granite  and 
gnedss. 


CEOLOGIC.y.  MAP  OF  THE  VOLCANO  OF  CRANDALL  BASIN,.  ABSAROKA  IL\NGE 

Scale 


Scale 

CONTOUR  INTERVAL  500  FEET 


=3 ?"' 


MILES 


GHXKUAL  FEATURES.  217 

by  Crandall  Crook,  extondiufj"  a  short  distance  into  the  Park.  It  is  defined 
by  the  aceoinpanvinfi-  map  (PI.  XXVII).  Tlie  area  of  voUianic  rock.s  liere 
re})resented  is  but  a  small  portion  of  the  great  belt  of  igneous  material 
that  forms  the  mountains  of  the  Absaroka  Range,  which  stretches  along  the 
eastern  margin  of  the  Yellowstone  Park  from  the  Bowlder  Plateau  on  the 
north  to  the  Wind  River  Mountains  on  the  south.  The  volcano  of  Crandall 
Basin  is  one  of  a  chain  of  volcanic  centers  situated  along  the  northern  and 
eastern  border  of  the  Yellowstone  Park,  which  are  all  distinguished  by  a 
greater  or  less  development  of  radiating  dikes,  and  by  a  crystalline  core, 
eroded  and  exposed  to  a  variable  extent.  Electric  Peak  and  Sepulchre 
Mountain  constitute  one  of  these  centers. 

Since  the  volcanic  ejectamenta  forming  the  Absaroka  Range  have 
been  thrown  from  numerous  centers  situated  at  no  great  distance  from  one 
another,  it  would  be  impossible  to  separate  the  materials  which  have  origi- 
nated from  the  different  vents,  since  they  must  have  intermingled;  and  it 
would  be  incorrect  to  assume  that  any  particular  area  of  volcanic  rocks 
had  been  derived  exclusively  from  one  center  of  eruption.  But  since  the 
material  ejected  from  closely  associated  vents  may  be  considered  to  have 
come  from  the  same  general  source,  or  to  belong  to  a  connected  series  of 
eruptions,  we  may  regard  the  volcanic  rocks  occurring  in  the  immediate 
vicinity  of  a  well-marked  center  of  eruption  as  representing  the  various 
results  of  volcanic  activity  which  have  existed  at  that  place.  The  area 
embraced  within  the  limits  of  the  map  may  not  be  sufficiently  large  to 
include  all  of  the  material  thrown  out  from  the  minor  centers  of  eruption, 
which,  during  the  period  of  volcanic  activity,  must  have  shifted  about  within 
the  region  of  Crandall  Basin,  but  it  is  large  enough  to  furnish  data  from 
which  the  geological  history  of  this  particular  volcano  may  be  derived. 

To  understand  the  geology  of  so  limited  an  area  as  that  represented 
on  the  map  it  will  be  necessary  to  explain  the  general  features  of  the  sur- 
rounding region.  A  high  and  massive  range  of  Archeau  granite  and  gneiss 
forms  the  country  north  of  Clark  Fork  and  stretches  in  a  northwest-southeast 
direction.  The  river  channel  is  situated  within  this  granitic  district,  near 
its  southern  margin.  The  Paleozoic  strata  which  overlie  the  Archean  rocks 
have  been  greatly  eroded,  leaving  an  irregular  layer  of  limestone,  which 
dips  gradually  to  the  southwest.  This  limestone  forms  a  cliff  along  the 
south  side  of  Clark  Fork  and  extends  for  considerable  distances  up  the 


218  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

valleys  of  the  streams  emptying  into  it  from  the  south.  It  also  extends 
down  the  valley  of  Soda  Butte  Creek  near  to  the  mouth  of  Amphitheatre 
Creek,  and  disconnected  areas  of  it  occur  at  the  mouth  of  Pebble  Creek 
and  near  Soda  Butte,  as  described  in  the  previous  chapter.  It  also  forms 
the  head  of  Pebble  Creek  and  the  valley  of  Slough  Creek,  a  small  portion 
of  which  is  shown  in  the  northwestern  corner  of  the  map.  The  limestone 
embraces  the  Cambrian,  Silurian,  and  Devonian,  which  attain  a  thickness 
of  only  1,800  feet,  the  strata  of  the  last  two  jDeriods  being  very  poorly 
developed  and  not  exceeding  in  thickness  400  feet.  In  most  places  the 
limestone  extends  up  into  the  Carboniferous.  The  whole  series  is  very 
jjoor  in  fossils  within  the  area  of  the  map,  and  the  identification  of  the 
horizons  rests  on  evidences  obtained  from  neighboring  sources. 

The  very  irregular  form  of  the  eroded  surface  of  the  limestone  is  shown 
by  the  variable  heights  of  the  limestone  cliffs,  which  range  from  400  to 
2,400  feet.  The  highest  within  the  area  are  in  the  peak  southwest  of  Cook 
City,  in  Hunter  Peak,  and  in  the  escarpment  south  of  the  mouth  of  Cran- 
dall  Creek.  The  extensive  erosion  which  preceded  the  ejection  of  the  lavas 
was  stibsequent  to  the  orographic  movement  that  involved  the  coal-beai'ing 
Laramie  strata  in  this  region.  Upon  this  greatly  eroded  surface  were 
thrown  volcanic  tuffs  and  scoria,  with  occasional  streams  of  lava,  until  the 
accumulation  exceeded  in  thickness  4,000  feet.  The  breccias  were  traversed 
in  various  directions  by  dikes  of  lava  which  filled  the  crevices  made  during 
the  later  eruptions. 

The  close  of  volcanic  acti^aty  in  the  vicinity  of  Crandall  Basin  was 
followed  by  another  period  of  erosion  which  removed  the  upper  portion  of 
the  volcanic  accumulation,  leaving  over  4,000  feet  of  it  in  the  form  of  high 
ridges  and  peaks,  with  deeply  cut  valleys  between.  The  occurrence  of 
nearly  horizontal  layers  of  massive  lava  alternating  with  crudely  bedded 
tuflfs  and  breccia,  which  in  places  are  piled  one  on  another  to  the  number 
of  twenty  or  more,  gives  rise  to  j^recipitous  mountains,  which  are  quite 
inaccessible  from  most  points  of  approach.  The  highest  of  these  is  Index 
Peak,  whose  steeple-like  summit,  11,700  feet  in  altitude,  has  not  yet  been 
scaled.  A  view  of  this  peak  from  Clark  Fork  gives  an  idea  of  its  sharpness. 
(PI.  XXVIII.)  The  readiness  with  which  the  scoriaceous  breccia  and  tuflfs 
are  eroded  causes  the  di'ainage  channels  to  be  narrow  and  rocky,  so  that  the 
valleys  traversing  this  region  are  in  general  very  difficult  to  travel  through. 


EARLY  ACID  BRECCIA.  219 

After  erosion  had  reduced  the  breccia  coiintr}'  to  very  near  its  present 
configuration,  the  region  to  the  southwest  was  flooded  Ijy  an  immense  body 
of  rhyolitic  lava.  One  edge  of  this  rhyolite  covered  a  portion  of  the 
breccias  in  a  thin  sheet,  remnants  of  which  are  found  in  the  southwestern 
part  of  the  district.  They  occur  in  the  most  unlooked-for  places,  as,  for 
instance,  at  an  elevation  of  10,000  feet  on  a  narrow  spur  near  the  summit 
of  Saddle  Mf>untain  and  at  various  altitudes  over  its  slopes;  also  near  the 
bottom  of  Cache  Creek  Valley,  where  they  form  a  bench  between  the 
levels  of  7,500  and  8,000  feet.  The  rhyolite  was  erupted  from  a  distinctly 
different  center  and  after  the  volcano  of  Crandall  Basin  had  long  become 
extinct,  so  that  it  need  not  be  considered  in  connection  with  the  history  of 
this  volcano. 

After  the  rhyolite  had  been  in  turn  eroded  and  the  valley  of  Lamar 
River  had  been  cut  500  feet  below  the  surface  on  which  the  rhyolite  had 
flowed,  basalt  was  again  erupted  and  filled  the  bottom  of  the  valley.  The 
source  of  this  eruption  has  not  been  discovered.  The  period  of  volcanic 
activity  may  be  considered  as  not  yet  ended,  though  it  is  at  present  con- 
fined to  such  manifestations  as  are  found  in  geysers,  hot  springs,  and  fuma- 
roles,  some  of  which  occur  within  the  district  under  discussion. 

The  general  features  of  the  region  having  been  sketched,  the  geology  of 
the  volcanic  rocks  within  the  area  of  the  map  may  be  taken  up  and  described 
in  greater  detail. 

EARLY  ACID  BRECCIA. 

The  breccias  and  lavas  covering  the  country  are  essentially  basaltic, 
but  there  are  remnants  of  an  older  breccia  which  is  acid.  The  term  brec- 
cia is  used  for  subaerial  accumulations  of  tuff  and  scoria  and  fragments 
of  I'ock  dei'ived  from  explosive  action,  and  it  will  be  seen  how  great  a  pro- 
portion of  all  of  the  material  has  been  subjected  to  this  kind  of  action. 
The  acid  breccia  is  found  underlying  the  basaltic  lavas  in  several  locali- 
ties in  the  district.  It  is  exposed  about  Republic  Creek,  where  it  is  rudely 
bedded,  the  bedding  being  produced  by  layers  of  different  mixtures  of  tuff 
and  angular  fragments.  They  pitch  steeply  to  the  south  and  pass  under 
basaltic  breccia,  which  also  is  rudely  bedded  at  the  bottom,  but  becomes 
well  bedded  higher  up.  The  lower  layers  dip  steeply  to  the  south  and 
southwest,  but  the  upper  layers  are  nearly  horizontal.  The  acid  breccia 
is  light  colored  and  variegated,  and  consists  of  horublende-mica-audesite 


220     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

mixed  with  some  pyroxene-andesite.  It  is  also  exposed  in  the  valley  of 
Cache  Creek  in  two  places,  the  larger  exposure  extending  for  about  8  miles. 
Here  it  is  light  colored  and  consists  of  the  same  kinds  of  andesite.  It  is 
indurated  and  somewhat  decomposed,  and  its  surface  indicates  that  it  was 
eroded  before  the  basaltic  breccia  was  thrown  on  it.  A  much  smaller  body 
of  honiblende-mica-andesite-breccia  occurs  in  the  heart  of  the  district  within 
a  mile  of  the  center  of  the  volcano.  It  is  at  the  junction  of  Closed  Creek 
and  Timber  Creek,  and  rests  directly  on  limestone,  as  it  also  does  in  the 
vicinity  of  Republic  Creek.  It  appears  to  have  been  at  one  time  on  the 
outskirts  of  the  earlier  volcanic  district,  for  its  lowest  portion  is  composed 
of  layers  of  andesitic  gravel  which  were  deposited  by  water.  It  passes  tip 
into  light-colored  breccia  of  liorublende-mica-andesite,  which  carries  frag- 
ments of  Archean  rocks.  Fragments  of  gneiss  and  schist  characterize  the 
early  acid  breccia  wheiever  it  has  been  found  along  the  northern  boundary 
of  the  Yellowstone  Park.  They  have  already  been  mentioned  as  occurring 
in  that  which  forms  the  base  of  Sepulchre  Mountain,  and  they  occur  in  that 
at  the  base  of  the  Washburne  volcano.  This  early  acid  breccia  has  been 
shown  by  Mr.  Hague  ^  to  belong  to  the  Eocene  period,  and  to  correspond  to 
the  Fort  Union  horizon.  Throughout  the  remainder  of  the  district  the 
basaltic  breccia  rests  directly  on  tlie  sedimentary  strata,  or  forms  the  bottom 
of  the  valleys  where  erosion  has  not  yet  cut  through  them  to  the  underlying 
rocks.  It  is  to  be  remarked  that  the  basaltic  lavas  pass  under  a  second 
series  of  acid  breccias  of  hornblende-mica-andesite,  which  are  like  the  older 
ones  in  mineralogical  character.  The  younger  or  late  acid  breccias  form  a 
considerable  part  of  the  Absaroka  Range  south  of  Lamar  River.  Neither 
the  older  nor  the  younger  of  these  accumulations  of  hornblende-mica- 
andesite  appears  to  have  been  erupted  from  what  we  have  called  the  volcano 
of  Crandall  Basin.  This  was  essentially  a  basaltic  center,  the  last  erujDtions 
of  which  became  acid,  and  in  part  more  basic,  but  were  of  small  extent. 

BASIC  BRECCIA  AND  FLOWS. 

A  conception  of  the  magnitude  and  pi-oportions  of  this  volcano  must 
be  derived  from  a  study  of  the  geological  structure  of  the  basaltic  breccia 
and  flows — early  basic  breccia — for  nothing  remains  to  indicate  a  single 
line  of  the  original  form  of  the  mountain.     In  place  of  a  volcanic  cone 

.    '  Hague,  Arnold,  The  age  of  the  igneous  rocks  of  the  Yellowstone  National  Park :  Am.  Jour.  Sci., 
4th  series,  Vol.  I,  1896,  p.  450. 


IJEDDED  BASIC  BRECCIA.  221 

there  is  a  system  o{  narrow  ridges  and  valleys,  three  of  the  deepest  valleys 
passing-  through  what  was  the  center  of  the  volcano.  The  arrangement  of 
the  rocks,  however,  is  so  marked  that  there  can  be  no  doubt  about  the  loca- 
tion of  the  center  of  volcanic  activity  or  of  the  general  nature  of  the 
mountain. 

DISTINCTLY   BEDDED   HUECCIA. 

The  geologist  who  approaches  the  region  by  way  of  the  Lamar  River 
is  impressed  with  the  great  masses  of  almost  horizontallj^  bedded  breccia 
which  form  the  chocolate-brown  mountains  on  either  side  of  Soda  Butte 
Creek.  They  are  finely  shown  in  the  panoi-amic  sketch  by  Prof.  W.  H. 
Holmes  in  his  report  on  the  geology  of  the  Yellowstone  Park,^  notices  of 
this  portion  of  the  country  being  found  on  pages  44  to  49.  The  sketch  is 
as  faithful  to  nature  as  it  is  artistic,  and  it  is  possible  to  calculate  the  point 
from  which  it  was  made  by  reference  to  the  map. 

The  breccias  rise  from  2,000  to  3,000  feet  above  the  river,  and  appear 
so  uniformly  bedded  as  to  give  the  impression  that  they  have  been  water- 
laid;  but  a  nearer  view  shows  their  irregularity  and  proves  their  subaerial 
deposition.  Upon  examination  the  bedding  is  found  to  be  crude  and  ill 
defined,  the  layers  consisting  of  tutf  with  various-sized  fragments  of  scoria 
and  compact  rock.  Between  the  layers  are  occasional  sheets  of  massive 
lava.  In  some  places  the  tutfs  are  quite  light  colored  and  are  very  notice- 
able among  the  dark-brown  beds.  The  deposits  contain  the  stumps  and 
roots  of  trees,  whose  erect  position  shows  that  they  have  not  been  distm-bed 
since  they  were  buried  beneath  showers  of  dust  and  stones.  Their  situa- 
tion at  different  horizons  in  the  breccia  and  their  large  size  indicate  how 
great  a  time  must  have  elapsed  between  the  explosions  which  covered  the 
country  with  ddbris  in  beds  from  1  to  3  or  more  feet  in  thickness. 

A  more  or  less  distinct  and  nearly  horizontal  bedding  is  characteristic 
of  the  breccias  forming  the  mountains  west  of  Cache  Creek,  including  the 
ridge  from  Mount  Norris  through  The  Thunderer  to  the  great  wall  sur- 
rounding Amphitheatre  Creek.  The  east  face  of  this  ridge  is  shown  in 
PI.  XXIX,  from  a  photograph  which  was  taken  from  the  divide  at  the  head 
of  Republic  Creek.  The  same  breccias  form  the  jjrecipitous  ridges  on  both 
sides  of  Pebble  Creek,  and  are  well  exposed  in  the  face  of  Baronett  Peak, 
10,300  feet  in  altitude. 

'Twelfth  Ann.  Eept.  U.  S.  Geol.  and  Geog.  Surv.  Terr.,  Part  II,  1883,  pp.  1-62. 


222     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  horizontally  bedded  breccias  and  lava  flows  extend  eastward  across 
the  head  of  Cache  Creek  to  Index  Peak  and  the  range  of  peaks  immedi- 
ately south,  but  the  lower  portions  of  these  mountains  are  irregularly 
bedded.  The  upper  parts,  above  10,000  feet,  consist  chiefly  of  basalt  flows 
resting  one  upon  another,  with  occasional  intercalated  layers  of  breccia. 
This  is  also  the  case  at  the  summit  of  the  mountains  northeast  of  Amphi- 
theatre Creek,  and  southward  to  the  summit  of  Mount  Norris. 

The  ridge  between  Cache  Creek  and  Crandall  Basin,  with  its  western 
spurs,  is  composed  of  nearly  horizontally  bedded  breccias  with  few  lava 
flows.  They  carry  numerous  silicified  trunks  of  trees,  which  are  exposed 
in  a  standing  position  on  the  western  slopes  of  the  Needles.  Similarly 
bedded  breccias  extend  south  of  Cache  Creek  across  Calfee  and  Miller 
creeks,  and  form  the  plateau  west  of  Lamar  River  and  the  high  mountains 
south  of  its  head.  Here,  again,  in  the  upper  thousand  feet  massive  basalt 
flows  prevail,  forming  the  top  of  the  plateau  and  the  upper  portion  of  the 
peaks  just  mentioned.  In  this  vicinity  the  basalt  sheets  are  plainly  seen 
to  slope  gradually  to  the  Avest  and  southwest,  their  highest  present  altitude 
of  about  11,000  feet  being  found  on  the  summits  of  Castor  and  Pollux 
peaks.  Basalt  sheets  to  the  thickness  of  400  feet  cap  the  summit  of  Saddle 
Mountain,  at  10,400  feet  altitude,  where  irregularly  shaped  flows  of  vesicular 
and  scoriaceous  basalt  indicate  by  their  position  and  by  the  arrangement 
of  the  columnar  cracking  that  they  flowed  down  an  uneven  surface,  appar- 
ently a  drainage  channel,  sloping  toward  the  southwest. 

Occasional  flows  of  massive  basalt  occur  in  the  lower  portions  of  the 
series  of  basic  breccias  and  tuffs.  A  notable  one  is  found  near  its  base 
over  the  limestone  on  Soda  Butte  Creek  and  Lamar  River,  but  the  great 
bulk  of  the  lava  sheets  is  at  the  top  of  the  series.  Columnar  structure  is 
common  to  all  of  these  flows  except  when  very  thin  and  scoriaceous,  and 
they  possess  all  of  the  superficial  characteristics  and  variations  of  surface 
flows  of  basalt.  None  of  those  observed  in  the  localities  just  described 
appear  to  have  been  intruded  sheets. 

CHAOTIC   BRECCIA. 

In  striking  contrast  to  the  almost  horizontally  bedded  breccias  and 
flows  are  the  chaotic  and  absolutely  orderless  accumulations  of  scoriaceous 
breccia  which  form  the  mountains  and  ridges  about  the  head  of  Lamar 


o     ^ 
s     i 


CHAOTIC  BKECCIA.  223 

River  aiitl  MilliT  Creek  .ind  the  ceiitriil  })ortiun  ot  ('raiidall  Basin.  To  one 
who  has  spent  inui-h  time  among-  the;  well-be(hled  breccias  of  Two  Ocean 
Phiteau  and  of  tlie  greater  portion  of  the  Absaroka  Range,  nothing  could 
be  more  noticeable  than  the  difference  of  structure  exhibited  by  the  breccias 
in  the  locality  just  mentioned.  It  is  to  be  remarked,  however,  that  while 
this  difference  is  so  noticeable  in  extreme  cases,  there  is  no  sharp  line  to  be 
(b'awn  l)etween  the  different  areas  in  the  field,  and  from  the  nature  of  their 
origin  they  often  merge  into  one  another. 

The  most  typical  exposure  of  chaotic  breccia  has  become  well  known 
for  the  grotesqueness  of  the  shapes  assumed  by  the  rock  when  cut  by 
erosion  into  pinnacles  and  buttresses.  The  heterogeneous  agglomeration  of 
scoria  and  tuffs  with  angular  masses  of  various  sizes  has  been  carved  into 
turrets  of  the  most  irregular  and  remarkable  shapes,  whose  dark  color  and 
forbidding  aspect  suggest  to  a  fanciful  imagination  goblins  and  demons, 
popularly  termed  "hoodoos." 

The  Hoodoo  Basin,  at  the  southern  base  of  the  mountain  of  the  same 
name,  is  the  best  example  of  this  form  of  erosion.  Other  occurrences  of 
this  character  are  found  in  various  localities  in  the  district  Some  of  the 
grotesque  pinnacles  are  shown  in  PI.  XXX,  from  a  photograph  taken  by 
Mr.  Weed.  The  rocks,  though  dark  chocolate-brown  as  a  whole,  often 
appear  on  closer  examination  to  be  brilliantly  colored  and  variegated, 
ranging  from  brick  red  to  purple  and  pink,  and  being  in  places  bluish  and 
gi-eenish,  and  also  yellow  and  brown.  These  colors  are  characteristic  of 
the  chaotic  breccias  in  a  number  of  localities;  as,  for  example,  on  the 
eastern  slope  of  Parker  Peak,  on  the  divide  between  Miller  and  Papoose 
creeks,  and  on  that  east  of  the  head  of  Lamar  River.  There  is  a  noticeable 
increase  in  the  number  of  large  masses  of  rock  occurring  as  fragments  in 
the  breccia,  which  often  exceed  a  diameter  of  8  feet,  some  being  20  or 
more  feet  thick.  The  petrographical  character  of  the  rocks  forming  large 
areas  of  this  breccia  is  more  uniform  than  in  the  outlying  region  of  well- 
bedded  deposits,  where  fragments  with  quite  different  habits  maj^  be  found 
intermingled.  The  whole  accumulation  is,  besides,  more  scoriaceous  and 
slag-like. 


224  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

DIKES. 

A  Still  more  noticeable  feature  of  the  central  portion  of  tlie  district  is 
the  occurrence  of  dikes  which  form  prominent  walls  of  rock  traversing  the 
country  in  all  directions.  They  are  specially  numerous  in  the  region  of 
chaotic  breccia,  but  are  not  confined  to  it.  Owing  to  the  importance 
attached  to  the  position  and  trend  of  the  dikes,  it  has  been  thought  advisable 
to  describe  tliem  in  considerable  detail,  in  order  to  assure  the  reader  that 
their  location  on  the  map  is  the  result  of  careful  observation. 

In  the  southwestern  part  of  the  district  they  are  most  noticeable  cross- 
ing the  spurs  at  the  head  of  Miller  Creek,  where  they  were  observed  by 
Superintendent  Norris.  They  are  nearly  all  parallel,  and  trend  northeast 
and  southwest,  a  few  having  a  more  westerly  direction.  Eight  of  them  cut 
the  slope  of  the  amphitheater  at  the  northern  base  of  Parker  Peak.  They 
are  from  3  to  8  feet  wide,  and  often  rise  from  3  to  15  or  20  feet  above  the 
ground.  They  are  nearly  vertical  and  parallel,  almost  straight,  with  slight 
curves  and  sometimes  sharp  bends,  and  may  be  traced  by  the  eye  across 
the  spurs  in  a  north-northeasterly  direction.  The  long  spur  south  of  the 
branch  of  Miller  Creek  is  crossed  hj  several  dikes  having  a  northeast  trend. 
They  consist  of  the  same  kinds  of  rock  as  two  dikes  cutting  the  summit  of 
Saddle  Mountain,  Avhich  also  have  the  same  trend  and  appear  to  be  continua- 
tions of  these  dikes. 

Hoodoo  Mountain  and  the  ridge  between  Lamar  River  and  Timber 
Creek  are  traversed  by  numerous  dikes,  some  of  which  trend  about  N.  10° 
W.  and  N.,  and  others  S.  30°  E.  and  SE.  Most  of  these  dikes  are  from  3 
to  8  feet  wide. 

Proceeding-  from  Hoodoo  Mountain  northwest  and  north,  one  finds 
that  the  divide  between  Miller  and  Timber  creeks  is  cut  by  dikes  trending 
northeast;  and  the  high  ridge  through  Indian  Peak,  and  the  Peak  itself, 
are  traversed  by  dikes  trending  N.  30°  E.  and  N.  20°  E.  In  this  peak,  as 
at  Saddle  Mountain,  the  dikes  cut  the  massive  flows  of  basalt,  which  were 
therefore  some  distance  beneath  the  surface  of  the  volcano  when  the  dikes 
were  injected. 

The  valley  of  Timber  Creek  is  covered  with  a  heavy  growth  of  pines 
and  firs,  which  obscures  the  geology  and  prevents  the  location  of  dikes 
except  by  closer  study  than  there  was  opportunity  to  bestow  on  it.  But 
the  long  narrow  ridge  north  of  this  branch  is  bare  of  timber  on  its  crest, 


DIKES  IN  CRANDALL  BASIN.  225 

iind  is  deeply  furrowed  by  lateral  •■■ulches  with  r(ick\'  spurs,  wliose  U])])er 
slopes  are  thiulv  elad.  'i'lio  geological  structure  of  this  ridge  is  specially 
significant  and  was  carefully  studied.  The  breccia  composing  it  at  its 
southern  base  is  l)asaltic  and  scoriaceous,  with  massive  flows  of  vesicular 
l)asalt  of  the  same  j)etrographical  habit.  On  one  f)f  its  southern  spurs, 
about  5.^  miles  from  its  eastern  end,  a  number  of  dikes  trend  N.  70°  E. 
Near  the  toj)  of  the  ridge  two  trend  N.  80°  E.,  and  one  trends  east.  They 
vaiy  in  width  from  18  inches  to  8  feet.  A  narrow  dike  near  the  top  trends 
S.  10°  E. 

On  the  crest  of  the  ridge,  about  a  mile  and  a  half  from  its  western 
end,  there  is  a  light-gray  indurated  tuff,  in  places  containing  small  frag- 
ments of  rock  and  carrying  some  })lant  remains.  The  northern  face  of  the 
ridge  at  this  point  is  an  almost  vertical  precipice,  exposing  breccia  without 
a  trace  of  bedding,  utterly  chaotic,  slaggy,  and  scoriaceous,  containing  large 
fragments  of  massive  basalt.  In  some  places  it  is  composed  of  small  angular 
fragments;  in  others  it  is  brightly  colored,  and  is  cut  by  dikes  which  trend 
a  little  north  of  east,  very  nearly  parallel  to  the  crest  of  the  ridge. 

About  a  mile  east  of  this  point  the  breccia  consists  of  vesicular  basalt, 
with  A'ery  large  feldspar  phenocrysts.  Some  masses  of  this  rock  are  20 
feet  in  diameter.  Near  this  an  amphitheater  on  the  north  side  of  the  ridge 
exposes  alternating  layers  of  breccia  and  lava  flows,  having  a  rather  steep 
dip  to  the  southeast.  They  appear  to  have  been  part  of  a  small  cone  at 
one  time.  This  part  of  the  ridge  is  cut  by  dikes  trending  a  little  north  of 
east,  and  also  by  a  broad  dike,  10  feet  wide,  trending  north  and  south,  with 
a  steep  hade  to  the  west.  Farther  east  on  the  crest  of  the  ridge  the  breccia 
becomes  indurated  and  weathers  into  small  fragments.  It  continues  to  be 
indurated  eastward  as  far  as  explored.  It  is  traversed  by  dikes  trending 
N.  50°  E.,  and  by  one  dike,  18  feet  wide,  running  S.  85°  E.  Farther  east 
there  are  other  dikes  cutting  the  ridge  in  a  northeasterl}'  direction  and 
trending  toward  the  two  deep  gulches  on  Hurricane  Mesa,  on  the  northern 
side  of  Closed  Creek  brancii  of  Crandall  Creek.  Some  of  the  dikes  are 
narrow,  but  several  are  quite  large,  one  being  10  feet  and  another  18  feet 
wide.  Along  the  portion  of  the  ridge  ex^jlored  b}^  the  writer,  a  distance 
of  about  4  miles,  there  are  31  dikes;  of  these  26  are  basalt  and  5  are 
hornblende-mica-andesite.  They  are  not  uniformly  distributed  along  the 
crest  of  the  ridge,  but  occur  in  groujjs  of  from  3  to  8,  the  largest  groups 

MON   XXXII.  PT   II 15 


226  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

beinar  situated  at  the  east.  Besides  these  dikes  others  were  observed  at  the 
eastern  end  of  the  ridge,  and  6  or  7  were  found  by  Mr.  Weed  at  the  western 
end,  making  over  40  in  all. 

From  the  distribution  and  trend  of  these  dikes  it  is  evident  that  they 
radiate  from  that  portion  of  Hurricane  Mesa  which  is  situated  between  the 
deep  gulches  just  alluded  to.  The  dikes  are  not  absolutely  straight,  but 
trend  in  general  toward  this  spot.  They  are  more  numerous  directly  south 
of  it,  where  the  ridge  is  nearest  to  this  center,  and  are  less  frequent  toward 
the  west,  where  the  ridge  is  more  remote. 

The  southern  slope  of  the  ridge  north  of  Timber  Creek  is  traversed 
by  dikes  of  the  same  kinds  of  rocks  as  those  occurring  on  the  crest,  and 
having  similar  trends,  leaving  no  doubt  that  they  are  continuations  of  the 
same  dikes.  The  breccia  cut  by  these  dikes  is  indurated  where  they  are 
close  together.  It  is  to  be  remarked  that  all  parts  of  the  country  in  this 
vicinity  which  were  explored  were  found  to  be  traversed  by  dikes,  but, 
owing  to  the  limited  amount  of  time  and  the  difficulty  of  traveling,  a  thor- 
ough exploration  of  the  country  was  not  made,  and  only  those  dikes  which 
were  observed,  sometimes  from  a  distance,  have  been  mapped,  their  probable 
continuations  being  indicated  by  dotted  lines. 

On  the  end  of  the  northeastern  spur  of  Indian  Peak  there  are  dikes, 
some  of  which  trend  west  of  north  toward  the  center  on  Hurricane  Mesa, 
while  others  trend  northeast.  Dikes  trending  northeast  occur  on  the  ridge 
between  Papoose  and  Hoodoo  branches  of  Crandall  Creek. 

The  structure  of  Hurricane  Mesa  and  the  ridge  west  is  clearly  seen 
from  the  ridge  south  of  it.  A  sketch  of  it  was  made  from  a  point  on  the 
northeast  spur  of  Indian  Peak  (PI.  XXXI).  It  shows  the  ridge  with  its 
eastern  table-land,  from  10,000  to  10,600  fee;  in  ahitude,  and  the  western 
chain  of  peaks,  reaching  heights  of  from  10,400  to  10,800  feet;  the  valley  of 
Closed  Creek,  whose  bottom  has  been  eroded  down  to  8,000  and  6,800  feet; 
the  steep  narrow  ridge  south  of  the  latter,  whose  high  point  in  the  middle 
ground  is  9,600  feet,  and  the  valley  of  Timber  Creek,  with  the  divide  to 
Cache  Creek,  at  about  9,500  feet.  To  the  right  is  the  outline  of  Hunter 
Peak,  at  the  mouth  of  Crandall  Creek. 

The  western  head  of  the  valley  of  Closed  Creek,  which  is  the  divide 
to  Cache  Creek,  consists  of  horizontally  bedded  breccia  with  a  slight  dip 
to  the  southwest.     It  contains  a  few  intercalated  flows  of  basalt  and  is  cut 


U  S.GEOLOOtCAL     SURVEY 


MONOGRAPH    XXXII     PA«T  II     PL  XXXI 


J-Plddinja 


HURRICANE      RIDGE 


DIKES  IN  ORANDALL  BASIN.  227 

by  dikes  trending  east  and  west.  The  bedded  breccias  continue  eastward 
across  the  saddle  to  the  tirst  peak  of  the  ridge  west  of  Hurricane  Mesa. 
Near  the  suniniit  of  this  peak  they  are  cut  off  and  overlain  by  beds  of 
breccia  dipping  slightly  toward  the  east.  These  beds  pass  under  the  massive 
rocks  which  form  the  upper  600  or  700  feet  of  the  western  half  of  this  ridge. 
The  massive  rocks  form  nearly  horizontal  sheets  capping  the  peaks  of  this 
part  of  the  ridge  and  constituting  the  top  of  the  flat  eastern  half  or  mesa. 
They  exhibit  prismatic  cracking,  and  appear  to  be  sheets  of  basalt  intruded 
in  the  breccia.  Beneath  them  the  breccia  shows  no  bedding,  and  in  the 
eastern  part  of  the  ridge — that  is,  in  the  mesa — it  is  highl)-  indurated  and 
weathers  like  massive  crystalline  rock  with  long  talus  slopes  of  small 
fragments. 

On  the  southern  side  of  the  head  of  Closed  Creek  the  bedded  breccias 
of  the  Cache  Creek  divide  are  cut  off  near  the  top  of  the  ridge  between 
Closed  and  Timber  creeks,  and  are  overlain  by  chaotic  slaggy  breccia, 
which  exhibits  a  rude  bedding,  with  steep  dip  to  the  eastward.  Halfway 
up  the  northern  slope  of  the  ridge,  beneath  this  point,  there  is  a  large 
iiTegularly  shaped  body  of  massive  columnar  rock  intruded  in  the  breccia. 
Exposures  of  massive  hornblende-mica-andesite  were  observed  by  Mr.  Weed 
on  the  southern  side  of  the  ridge  opposite  to  this  body. 

The  southern  slope  of  the  ridge  west  of  Humcane  Mesa  is  traversed 
by  dikes  rvmniug  east  and  west  and  more  or  less  parallel.  As  already 
remarked,  the  eastern  half  of  the  ridge  is  a  high  table-land,  whose  top,  at 
10,200  feet,  consists  of  a  horizontal  sheet  of  basalt,  200  to  300  feet  thick. 
On  the  south  there  are  steep  slopes  and  spurs,  with  much  slide  rock  and 
little  vegetation.  On  the  north  are  four  deep  amphitheaters,  with  precipitous 
walls,  and  high  rocky  spurs  between  them.  In  the  middle  of  the  table-land 
on  the  southern  side  are  two  narrow  gulches  encircling  a  round-topped  spur. 

At  the  western  end  of  this  table-land  dikes  are  numerous.  Across  its 
southwestern  spur  there  are  11,  from  2  to  10  feet  wide,  trending  N.  70°  E. 
and  S.  70°  E.  At  the  northwestern  end  of  the  plateau  there  are  dikes 
trending  northwest,  which  are  well  exposed  in  the  wall  of  the  amphitheater. 
A  10-foot  dike  follows  the  ridge  along  the  saddle  and  cuts  the  turreted  peak 
to  the  northwest.  The  dikes  also  cut  the  basalt  sheets.  The  long  spur 
north  of  this  end  of  the  plateau  is  traversed  by  18  narrow  dikes  trending 
toward  the  northwest  and  converging  southeastward  toward  the  round- 


228     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

topped  spur  in  the  middle  of  the  plateau.  Small  dikes  cut  the  northern 
edge  of  the  plateau  and  a  small  spur  from  it,  and  trend  toward  the  north- 
west at  various  angles.  They  can  be  seen  at  a  distance  of  4  or  5  miles 
traA'ersing  the  country  to  the  north  in  the  same  direction,  but  of  course  it 
is  onl}'  the  largest  and  most  prominent  that  can  be  recognized  in  this  way. 

The  basalt  sheet  on  top  of  the  plateau  is  massive  and  is  jointed  in 
large  rectangular  blocks.  The  walls  of  the  amphitheater  appear  to  consist 
of  similar  massive  rock  for  a  depth  of  a  thousand  feet,  but  they  are  highly 
indurated  breccia. 

The  western  half  of  the  mesa  is  cut  off  by  the  gidcli  west  of  the 
round-topped  spur,  and  presents  a  cliff  facing  eastward.  This  is  intersected 
by  numerous  dikes,  one  of  which  is  12  feet  wide.  The  cliff  passes  south 
into  the  pinnacled  spur  west  of  the  gulch. 

A  high  and  narrow  ridge  extends  around  the  northern  side  of  the  head 
of  the  twin  gulches,  and  consists  of  massive  rock  cut  by  a  few  dikes  trend- 
ing north.  From  it  a  high  spur  runs  toward  the  northeast.  It  is  composed 
of  chaotic  breccia,  which  is  somewhat  indurated  and  is  traversed  by  a 
numljer  of  dikes  ti'ending  northeast. 

The  i)ortion  of  Hurricane  Mesa  east  of  the  twin  gulches  is  less 
indurated  than  that  immediately  west,  and  contains  fewer  dikes.  Its 
northern  side  was  not  explored,  but  undoubtedly  exhibits  some  dikes. 
Across  the  upper  part  of  the  southern  slope  there  is  a  long  straight  dike 
trending  south  of  east;  and  several  others  occur  lower  down  the  slope,  and 
trend  toward  the  round-topped  sjjur.  The  southeastern  spurs  are  traversed 
by  10  dikes,  which  trend  toward  the  northeast  and  converge  toward  a  point 
in  fche  gulch  which  drains  the  eastern  end  of  the  mesa.  Near  this  point  on 
the  long  eastern  spur  the  breccia  is  indurated  and  a  large  body  of  fine- 
grained crystalline  rock  is  exposed,  which  is  probably  connected  with  the 
center  toward  which  this  group  of  dikes  converge.  Near  the  junction  of 
Closed  and  Timber  creeks  a  number  of  dikes  were  observed,  most  of  which 
trend  toward  the  northeast.  There  is  a  large  one  trending  toward  the 
round-topped  spur.  Where  the  two  systems  of  dikes  intersect,  tlie  dikes 
from  the  round-topped  spur  are  found  to  be  the  younger,  since  they  cut 
those  trending  toward  the  eastern  center. 

These  observations  have  been  plotted  on  the  map  in  such  a  manner  as 
to  show  where  the  dikes  have  been  actually  found,  the  dotted  lines  being 


THE  COKE  OF  TllK  UlfANDALL  VOLCANO.  229 

introduced  to  emphasize  the  structure  and  indicate  where  the  dikes  would 
have  been  found  if  tliere  had  been  sufficient  time  to  liunt  them  out.  Slide 
rock  and  forest  obscure  ])arts  of  the  country,  and  })arts  of  it  have  not  been 
visited,  as  the  o-eneral  character  of  the  geology  was  recognizable  from  a 
distance.  From  the  data  obtained  there  can  be  no  reasonable  question  as 
to  the  arrangement  of  the  dikes.  The  great  majority  of  those  in  Craudall 
Basin  radiate  from  the  middle  of  Humcane  Mesa.  A  smaller  number 
radiate  from  a  second  center,  3  or  4  miles  east  of  the  first. 

It  was  during  the  study  of  the  district,  which  was  traversed  along  much 
the  same  lines  as  those  along  which  it  has  just  been  described,  that  the 
conviction  forced  itself  upon  the  writer  that  the  locality  toward  which  the 
majority  of  dikes  converged  nuist  have  been  the  center  of  great  volcanic 
activity,  and  would  prove  to  be  the  location  of  what  was  once  the  conduit 
or  throat  of  an  ancient  volcano,  and  mig-ht  ijossibly  exhibit  rocks  represent- 
ing a  coarsely  crystalline  development  of  the  magmas  which  had  filled  the 
dikes.  It  was,  consequently,  with  great  expectations  that  he  led  his  pack 
train  over  the  uninviting  and  even  forbidding  countrA'  drained  by  Crandall 
Creek,  from  Miller  Creek  across  the  densely  timbered  valley  of  Timber 
Creek,  and  over  the  precipitous  ridge  into  the  bottom  of  Closed  Creek ;  and 
having  reached  the  gulches  draining  the  suspected  core,  it  was  with  great 
satisfaction  that  he  found  himself  surrounded  bv  blocks  of  gabbros  and 
diorite  of  decidedly  coarse  grain.  Here  Avas  in  reality  the  core  of  an  ancient 
volcano,  the  conduit  through  wliich  lava  had  risen  to  the  surface,  from 
which  it  had  escaped  in  lateral  fisures  through  the  surrounding  rocks,  and 
in  which  it  had  eventually  solidified. 

A  description  of  this  core  necessarily  involves  a  consideration  of  the 
petrographical  character  of  the  rocks  composing  it,  which  in  the  case  of  the 
other  rocks  of  the  district  has  been  deferred  to  a  subsequent  part  of  this 
chapter;  and  in  order  to  maintain  a  logical  sequence  in  the  study  of  all  of 
the  rocks  of  this  volcano  the  detailed  description  of  the  granular  core  will 
be  given  in  connection  with  the  jjetrography  of  the  rocks.  A  general 
statement  of  its  character,  however,  will  be  in  place  here. 

The  round-topped  spur  between  the  twin  gulches,  frequently  referred 
to,  consists  of  granular  gabbro  which  grades  into  diorite.  Grabbro  also 
forms  the  bottom  of  the  gulches  and  extends  up  the  flanks  of  the  precipitous 
spurs  encircling  the  gulches.     The  greater  part  of  the  spur  on  the  west 


230  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

above  the  timber  is  gabbro,  which  here  attains  its  highest  degree  of  crystal- 
hzatiou.  The  outhne  of  the  gabbro  mass  is  not  well  defined  against  the 
surrounding  breccias,  for  several  reasons.  The  breccias  become  highly 
indurated  as  they  approach  the  core,  and  finally  appear  as  dense  aphanitic 
rock,  with  jointing  planes  like  those  of  the  finer-grained  parts  of  the  massive 
intruded  rocks,  and  evidences  of  their  originally  brecciated  character  are 
almost  obliterated.  Moreover,  the  gabbro  becomes  finer  grained  and  darker 
colored  near  the  encircling  rocks,  and  in  some  places  is  so  fine  grained  as 
to  be  distinguished  with  difficulty  from  the  metamorjjhosed  breccia.  The 
shape  of  tlic  granular  core  is  very  irregular  and  indefinite,  for  it  is  found 
ujion  investigation  that  it  does  not  consist  of  one  continuous  body  of 
solidified  magma,  but  is  made  up  of  smaller  bodies  diff"ering  in  grain  and 
mode  of  crystallization  and  in  mineral  composition.  Many  of  these  bodies 
appear  as  dikes  or  veins  cutting  one  another  and  the  larger  masses  of 
gabbro.  They  penetrate  the  breccia  as  dikes  of  crystalline  ])orphyries, 
whose  identity  with  the  more  distant,  finer-grained  dikes  is  shown  by  then* 
megascopical  habit  and  mineralogical  character.  It  is  evident  that  in  the 
immediate  neighborhood  of  the  heated  conduit  they  cooled  at  a  rate  which 
permitted  them  to  assume  a  higher  degree  of  crystallization  than  that 
assumed  by  the  dikes  in  the  cooler  breccias.  The  transition  in  grain  from 
the  core  outward  is  rapid,  and,  owing  to  the  variability  in  the  size  of  the 
dikes  and  the  diff'erences  of  crystallization  due  to  this  cause,  no  definite 
ratio  of  change  was  noted. 

Returning  to  the  consideration  of  the  distribution  of  dikes,  it  is  to  be 
remarked  that  they  abound  in  the  breccias  lying  north  and  also  east  of  Cran- 
dall  Creek.  In  the  most  easterly  mountain  of  breccia  on  the  map,  and  on 
the  northwestern  spur  of  Windy  Mountain,  the  breccia  of  which  consists  of 
basaltic  scoria  and  flows,  there  are  numerous  dikes,  some  of  which  trend  a 
little  east  of  south  and  others  a  little  west  of  south.  The  high  limestone 
escarpment  north  of  Windy  Mountain  is  cut  by  many  small  vertical  dikes, 
whose  black  color  contrasts  strongly  with  that  of  the  whitened  limestone 
containing  them.  In  different  localities  in  Crandall  Creek  where  the  lime- 
stone is  cut  by  dikes  it  is  whiteiied  in  the  same  manner  in  the  vicinity  of  the 
intruded  rock.  These  dikes  also  trend  east  of  south,  and  it  is  to  be  observed 
that  there  were  no  signs  of  a  radiation  of  dikes  within  the  limestone,  but 
the  dikes  appeared  to  be  located  along  a  system  of  parallel  joints. 


DIKES  IN  ORANDALL  BASIN.  231 

No  (liki's  of  volcanic  rocks  were  found  in  the  g-neiss  and  g-ranite  alonj^ 
Clark  Fork,  altliough  the  baro  and  smootldy  glaciated  surfaces  offered 
ample  opportunity  for  detecting  tlieni  if  jjresent. 

The  stiaicture  of  the  high  ridge  north  of  the  upper  portion  of  Crandall 
Creek  is  shown  in  the  escarpment  on  its  northern  side — that  is,  along  the 
southern  side  of  Clark  Ft)rk  and  of  the  creek  south  of  Index  Peak.  Tlie 
basaltic  breccias  appear  to  be  rudely  bedded  at  various  angles  and  are  cut 
by  numerous  dikes.  The  top  of  the  western  end  of  the  ridge,  as  already 
stated,  consists  of  twenty  or  more  basalt  sheets,  which  are  nearly  horizontal. 
When  viewed  from  Hurricane  Mesa  it  appears  that  the  low,  rugged  peak 
about  4  miles  north  of  the  gabbro  core  consists  of  rough  beds  of  breccia 
dipjiing  steeply  eastward.  In  the  middle  of  the  ridge  which  is  being 
described  there  is  a  low  arch  of  breccia  beds  that  ai-e  rouech  and  irregular. 
Higher  up  on  the  peaks  to  the  west  the  bedding  is  more  regular  and  dips  at 
a  low  angle  to  the  southwest. 

At  the  eastern  end  of  the  ridge  the  breccias  resting  on  the  limestone 
are  traversed  by  dikes  trending  S.  10°  E.  One  of  special  importance  is  3 
feet  wide  and  trends  S.  25°  E.  It  rises  8  or  10  feet  above  the  surface  of 
the  ground  and  exhibits  horizontal  prisms.  It  will  be  referred  to  again  on 
account  of  its  composition  and  of  the  presence  of  large  crystals  of  primary 
quartz. 

The  southeastern  spur  of  Index  Peak  is  cut  by  dikes  trending  north- 
west and  southeast,  and  some  more  northerly.  Numerous  dikes  cut  the 
northern  and  northwestern  spurs  of  the  same  mountain,  and  a  few  were 
observed  on  the  ridges  surrounding  Republic  Creek. 

In  the  neighborhood  of  Cook  City  we  aj^proach  another  center  of 
eruptive  action,  which  manifests  itself  in  the  form  of  intrusive  sheets 
of  porphyry  that  occur  within  the  Cambrian  strata  along  the  valley  of 
Soda  Butte  Creek,  and  more  especially  in  the  mountains  north  of  Cook 
City,  just  beyond  the  limits  of  the  mapped  area.  Dikes  of  similar  rocks 
cut  the  breccia  of  Mount  Miller,  one  of  the  peaks  of  this  group  of  moun- 
tains. Several  intrusive  sheets  occur  in  the  limestone  south  of  Cook  City, 
and  are  located  on  the  map.  They  include  a  dense  porphyry,  a  fine- 
grained gabbro-porphyry,  and  hornblende-andesite.  A  few  miles  west  of 
Cook  City  there  ai-e  two  small  intrusions  of  dacite-porphyry. 


232  GEOLOGY  OF  THE  YELLOWSTO^fE  NATIONAL  PAEK. 

EXTENT   OF   EROSION. 

As  already  stated,  the  volcanic  ejeetamenta  were  thrown  over  the  sur- 
face of  greatly  eroded  sedimentary  rocks.  It  appears  from  a  study  of  the 
adjacent  region  that  an  apparently  conformable  series  of  deposits  from 
Cambrian  to  the  Laramie  of  the  Cretaceous  had  been  greatly  dislocated  and 
faulted,  and  in  places  entirely  eroded  down  to  the  crystalline  schists,  before 
the  volcanic  lavas  of  Crandall  Basin  were  erupted,  thus  representing  a  period 
of  great  orographic  movement  and  denudation.  It  becomes  equally  evident 
from  a  study  of  some  of  the  areas  of  volcanic  rocks  that,  after  the  earlier  of 
these  rocks  were  extravasated,  both  orographic  movement  and  denudation 
took  place  on  a  grand  scale.  The  region  of  Electric  Peak  and  Sepulchre 
Mountain  exhibits  the  extent  of  the  faulting  which  cut  in  two  that  andesitic 
volcano.  But  in  tlie  region  of  Crandall  Basin,  which  seems  to  have 
escaped  serious  disturbance  since  the  accumulation  of  the  basaltic  lava,  we 
may  discover  a  measure  of  the  erosion  which  has  affected  this  portion  of 
the  country  subsequent  to  the  completion  of  this  volcano,  which  must  have 
been  active  in  upper  Miocene  time.^  However,  it  should  be  confessed  at 
the  outset  that  all  such  calculations  must  be  of  the  crudest  and  most  general 
character. 

A  consideration  of  the  geological  structure  which  has  been  briefly 
sketched,  and  which  has  been  indicated  on  the  map  and  in  tlu-ee  vertical 
sections  across  the  district  through  the  gabbro  core,  leads  to  interesting  con- 
clusions. The  profile  sections  (PI.  XXXII)  are  drawn  to  natural  scale  and 
exhibit  the  steepness  of  some  of  the  mountains.  The  first  passes  through 
the  core  in  a  direction  N.  24°  E.,  and  cuts  Pollux,  Parker,  and  Indian 
peaks,  the  narrow  ridge  south  of  Hurricane  Mesa,  and  the  low  hills  north, 
ending  in  the  gneiss  on  Clark  Fork.  The  second  lies  N.  20°  30'  W.,  pass- 
ing from  the  di^^de  between  Crandall  and  Sunlight  basins,  through  the  gab- 
bro core  and  Index  Peak,  to  the  gneiss  at  the  head  of  Soda  Butte  Creek. 
The  third  passes  S.  77°  30'  E.,  from  Druid  Peak  across  the  valleys  of  Soda 
Butte  and  Cache  creeks,  cutting  the  ridge  of  The  Thunderer  where  it  is 
narrowest,  and,  traversing  nearly  the  whole  length  of  Hurricane  Mesa, 
passes  through  the  summit  of  Windy  Mountain. 

The  chaotic  accumulations  of  scoriaceous  breccia  and  the  occuiTences  of 
steeply  dipping  beds  and  lava  flows  throughout  the  area  of  Crandall  Basin 

'  Hague,  Arnold,  loc.  cit.,  p.  4.52, 


32 


n  S  GEOLOGICAL  SURVEY. 


DRUID  PEAK 


I 


MONOGRAPH  XXXII, PART  ILPL  >DCZII 


THE  THUNDERER 

-  --       rJebb"  — 


HURRICANE  MESA 


"TliJb 


TiiniLi]iiiimiri[iii[[it( 


mTinii|!;i|iiiiii|ii|||irinniiTmifiaif[IliiiiiiiiiiliiiiMiiJli/illlIill 


HURRICANE  MESA 


INDEX  PEAK 
Nebs 


POLLUX  PEAK 
y?!^N  e  b  s 


HURRICANE  MESA 
lebb 


Nebb 


J,  A-To.  Lllli   Baltbnol 


GEOLOGICAL  GROSS  SECTION'S  OF  THE  YOLCiVNO  OF  CKANDALL  BASIN, .VBSAll()IL\  RANGE 

CARBONIFEROUS  DEVONIAN  SILURIAN  CAMBRIAN  NEOCENE  EOCENE  ARCHEAN 


Cm 


sj 

«« 

N^d  Nrh  | 
Nebs  Hebb 


/Rgn 


Scale  oT  Miles 


1      i      o 


EliOSION  OF  THE  CKANDALL  VOLCANO.  233 

and  the  country  south  of  it  show  this  to  have  been  the  scene  of  great 
voU-anic  activity,  which  shifted  about  from  place  to  pLvce,  building  up  and 
blowing  to  pieces  cone  after  cone  of  moderate  proportions. 

The  unifonnly  bedded  tuffs,  breccias,  and  lava  flows,  which  dip  at 
anffles  not  exceeding  5°  and  form  the  mountains  west  and  southwest  of 
Crandall  Basin,  show  with  equal  clearness  that  they  cover  an  area  of  inac- 
tion, where  the  ejectamenta  and  lava  streams  remained  undisturbed  during 
their  accumulation.  The  same  is?  true  of  the  nearly  horizontal  beds  of  lava 
and  breccia  which  cap  chaotic  breccias,  as  at  Index  Peak.  Since  they 
began  to  accumulate  the  region  beneath  them  must  have  remained  quiet, 
however  active  it  had  been  previously,  for  they  exhibit  no  evidences  of 
upheaval.  These  subaerial  deposits  and  flows  must  have  been  derived  from 
some  neighboring  center  or  centers  of  eruption.  The  slope  of  the  lava 
flows  toward  the  west  and  southwest  and  their  petrographical  character 
prove  conclusively  that  they  have  been  erupted  and  ejected  from  centers 
situated  in  Crandall  Basin.  While  it  is  evident  that  the  breccia  within  this 
basin  and  the  lower  portion  of  the  bedded  breccia  surrounding  it  came 
from  shifting  vents,  it  seems  necessary  to  assume  that  the  lava  streams 
which  occupy  high  positions  near  the  summits  of  the  present  mountains 
must  have  flowed  from  still  higher  vents  on  the  slopes  or  summit  of  some 
great  volcano.  The  exploration  of  the  region  has  led  to  the  discovery 
of  one  large  central  conduit  and  a  multitude  of  radiating  channels  Avhicli 
extend  to  distances  of  from  7  to  ]  2  miles  from  the  center,  besides  another 
smaller  center. 

The  great  conduit  and  its  radiating  channels  belong  to  a  period  suc- 
ceeding that  in  which  the  chaotic  breccia  of  Crandall  Basin  was  thrown 
out,  and  to  one  in  which  the  volcanic  energy  had  concentrated  into  one 
place,  for  the  dikes  from  this  gabbro  core  traverse  the  country  in  nearly 
straight  lines,  and  have  not  been  thrown  into  confusion  b}'  the  breaking 
out  of  new  centers  of  eruption.  They  belong,  in  fact,  to  the  latest  phase  of 
volcanic  activity  in  the  district. 

The  coarsely  crystalline  character  of  the  rock  at  the  top  of  the  core, 
as  it  is  exposed  at  10,200  feet,  as  well  as  the  topography  of  the  country, 
makes  it  clear  that  very  considerable  erosion  has  taken  place  since  the 
volcano  was  active.  Hoav  great  the  erosion  may  have  been  will  appear 
when  the  attempt  is  made  to  combine  the  facts  just  mentioned  and  to  com- 
pare them  with  what  is  known  of  great  volcanoes  which  are  still  active. 


234  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

One  of  the  largest  and  most  thoroughly  investigated  active  volcanoes 
is  Etna,  whose  majestic  cone  rises  from  the  sea  to  a  height  of  10,835  feet. 
According  to  the  elaborate  study  of  Etna  by  Sartorius  von  Waltershauseu, 
as  completed  by  von  Lasaulx,^  the  central  mass  and  basal  portion  of  this 
mountain  consist  of  thick  beds  of  tuff  (or  breccia)  traversed  by  dikes  of 
massive  rock,  filling  clefts  which  are  for  the  most  part  nearly  vertical. 
Between  the  layers  of  tutf  or  breccia  are  sheets  of  crystalline  rock.  These 
are  partly  connected  with  the  dikes,  and  have  been  injected  horizontally  in 
the  tuff,  or  they  are  in  part  surface  flows  of  lava.  The  beds  in  the  central 
jjart  of  the  mountain  dip  as  steeply  as  29°,  and  show  by  their  positions  and 
by  the  different  groups  of  radiating  dikes  that  the  centers  of  eruption 
have  been  shifted  from  southeast  to  northwest.  The  lower  flanks  of  the 
volcano  are  composed  of  more  numerous  lava  flows,  and  slope  at  angles 
of  from  2°  to  5°.  These  lavas  have  been  mostly  erupted  from  lateral  or 
parasitic  cones,  the  arrangement  of  which  on  the  surface  proves  that  they 
all  belong  to  grovips  in  more  or  less  straight  lines  which  exhibit  an  exactly 
radial  direction  from  the  center  of  eruption — that  is,  the  present  crater  of 
the  volcano.  In  the  earlier  period  of  the  building  of  the  mountain,  as  at 
present,  fissures  were  formed  from  the  center  outward,  radially.  These 
fissures  often  lay  close  together,  and  were  then  almost  parallel;  through 
them  the  molten  lavas  rose  and  formed  dikes;  and  where  they  reached  the 
surface  they  gave  rise  to  parasitic  cones.  Modern  fissures  that  are  radial 
to  the  present  crater  are  those  of  1669,  1792,  1811,  1852,  1865,  1874,  and 
1879.  There  are  many  others  which  are  approximately  radial,  and  others 
exhibiting  no  such  arrangement.  The  lava  flows  on  the  flanks  of  the 
volcano  have  reached  the  surface  through  the  radial  fissures  connected  with 
the  central  conduit. 

The  profile  of  Mount  Etna  along  a  vertical  section  through  the  summit, 
from  Catania  to  Randazzo,  drawn  to  natural  scale,  is  shown  in  PI.  XXXII. 
The  scale  is  the  same  as  in  the  profiles  across  Crandall  Basin — i25;ooo. 
The  diameter  of  the  volcano  in  the  direction  taken  is  about  27  miles. 

Etna  is  of  very  recent  age,  geologically  considered,  for  its  lowest  rocks 
rest  on  Diluvial,  or  Pleistocene,  deposits,  since  which  period  it  has  piled 
up  scoria  and  lava  to  a  height  of  nearly  11,000  feet. 

From  the  foregoing  there  appears  to  be  a  close  analogy  between  the 

1  Der  ^tna,  Leipzig,  1880. 


COMPARISON  WITH  OTHER  VOLCANOES.  235 

conditions  at  present  existing-  in  the  active  basaltic  volcano  of  Etna  and 
tliose  which  |)rol)ably  olitained  in  the  basaltic  volcano  of  Craudall  Basin. 
In  the  last-named  region,  as  it  is  now  exposed,  four-fifths  of  the  volcanic 
material  is  fragmentary  ejectamenta,  forming  subaerial  breccias  of  angular 
pieces  of  massive  and.  scoriaceous  lava  with  tuff  or  dust.  But  in  the  upper 
pai"ts  of  the  outlying  mountains  massive  flows  of  lava  predominate.  In  the 
case  of  Mount  Etna  it  is  known  that  the  central  mass,  as  exposed  in  the 
Val  del  Bove,  is  mostly  fragmentary  ejectamenta,  but  the  surface  of  the  vol- 
cano consists  of  lava  flows  to  a  very  great  extent. 

In  Vesuvius  there  is  a  cone  of  nuich  steeper  slope,  consisting  largely 
of  tuff-breccias,  which  dip  at  high  angles  in  the  slopes  of  Monte  Somma. 
The  latest  eruptions,  which  form  the  cone  of  Vesuvius,  have  been  quiet 
outflows  of  lava.  A  meridional  profile  of  Vesuvius  on  the  same  scale  as 
that  of  Etna  is  placed  under  the  latter  for  comparison  (PI.  XXXII). 

It  is  to  be  remarked  that  the  subaerial  breccias  and  tufts  of  Monte 
Somma,  while  differing  in  mineral  and  chemical  comjDosition  from  those  of 
the  Crandall  district,  resemble  them  most  closely  in  outward  appearance 
and  in  the  manner  of  their  agglomeration.  The  subaerial  breccias  of  the 
Yellowstone  Park  and  its  vicinity  are  for  the  most  part  more  compact  than 
those  of  Monte  Somma,  but  exhibit  the  same  structure.  Many  of  them, 
however,  present  the  same  degree  of  cohesion  and  all  the  characteristics  of 
recent  ejectamenta. 

The  volcanoes  of  the  Hawaiian  Islands  are  said  to  be  the  results  of 
non-explosive  eruptive  action,  very  little  fragmentary  material  entering  into 
the  construction  of  the  mountains.  But  it  must  be  borne  in  mind  that  the 
central  portions  of  the  great  volcanoes  there  are  not  exposed  and  their  true 
character  is  not  definitely  known. 

Assuming  that  the  volcano  which  must  have  existed  in  the  region  of 
Crandall  Basin  resembled  closely  the  type  represented  by  Etna,  and  neglect- 
ing the  erosion  which  undoubtedly  removed  material  from  above  the  outlying 
peaks  of  horizontally  bedded  lavas,  we  may  gain  some  idea  of  the  original 
form  and  proportions  of  this  volcano  by  constructing  above  the  profile 
sections  through  its  center  the  outline  of  Etna,  as  represented  in  the  plate 
of  sections.  Placing  the  crater  of  Etna  over  the  center  of  the  dikes  of 
Crandall  Basin  (PL  XXXII),  and  allowing  its  outer  slopes  to  rest  on  the  sum- 
mits of  the  surrounding  mountains,  we  obtain  theoretical  elevations  of  the 


236  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Crandall  volcano,  which,  if  reckcmed  from  the  level  of  the  ancient  surface 
of  the  limestone  in  the  neighborhood  of  the  g-abbro  core,  are  13,000,  13,400, 
and  13,800  feet.  These  results  are  sufficiently  close  to  one  another  when 
it  is  noticed  that  the  jieaks  used  as  datum  points  lie  in  an  arc  of  133°  and 
at  distances  of  from  9  to  14  miles  from  the  center — from  Index  Peak  in  the 
north  to  Pollux  Peak  in  the  south.  Moreo^-er,  the  highest  altitude  is 
obtained  by  using  Pollux  Peak  as  a  base  of  reckoning,  and  this  mountain 
lies  within  the  radius  of  other  volcanic  centers  near  the  head  of  Stinking-- 
water  River,  and  has  probably  been  built  up  by  lavas  from  two  great 
centers. 

A  volcano  13,400  feet  in  elevation  with  a  radius  of  20  miles  is  not  so 
large  as  man}"  in  existence  at  the  present  day.  The  volcanoes  of  Hawaii 
are  familiar  examples.  Of  these.  Manna  Loa,  with  an  altitude  of  13,675 
feet,  has  a  maxinuim  radius  of  about  40  miles  and  a  minimum  radius  of  20. 
Mauna  Kea,  13,805  feet  in  height,  has  an  average  radius  of  20  miles.  These 
estimates,  it  should  be  remembered,  are  taken  from  the  sea  line.  The 
heights  of  these  volcanic  piles  above  their  actual  base,  and  the  real  diameters 
of  their  cones,  are  not  known.  The  profile  of  Kea  is  shown  on  the  same 
scale  as  that  of  Etna  and  has  nearly  the  same  outline  (PI.  XXXII).  A 
volcano  with  the  profile  of  Vesuvius,  if  as  large  in  diameter  as  Etna,  would 
be  5,800  feet  higher,  or  about  16,600  feet  in  height. 

The  conclusion,  therefore,  that  the  ancient  volcano  of  Crandall  Basin 
rose  to  an  elevation  of  13,400  feet  above  the  preexisting  surface  of  the 
limestone  is  within  reasonable  limits,  and  is  probably  too  low.  Upon  this 
basis  we  find  that  the  gabbro  core  in  Hurricane  Mesa  must  have  solidified 
at  a  distance  of  10,000  to  12,000  feet  below  the  level  of  the  ancient  crater. 
Erosion  must  have  removed  10,000  feet  from  the  highest  portion  of  the 
volcano  to  the  level  of  the  mountain  tops,  and  4,000  feet  more  into  the  val- 
leys between  them,  thus  cutting  14,000  feet  vertically  below  what  was 
once  the  summit  of  the  volcano.  At  Index  Peak  the  present  topography 
shows  an  erosion  of  nearly  5,000  feet  from  the  summit  of  the  peak  to  the 
valley  of  Clark  Fork. 

The  foregoing  estimates  were  based  on  the  assumption  that  the  tops 
of  the  highest  mountains  of  horizontal  lava  flows  had  not  been  materially 
afPected  by  erosion;  hence  we  must  regard  the  calculated  amount  of  erosion 
as  a  minimum.     There  seems  to  be  no  way  of  avoiding  this  conclusion, 


EAULY  ACID  BRECCIA.  237 

unless  we  conceive  the  last  act  of  vulcanisin  to  have  been  the  greatest  and 
imagine  a  gigantic  explosion  to  have  blown  the  ui)p(o-  })ai't  of  the  volcano 
into  the  air  and  t(»  have  left  no  evidence  of  such  a  culmination  of  events. 
On  the  contrar}-,  the  evidence  furnished  by  the  structure  of  the  granular 
core  indicates  that  the  last  eruptions  were  feeble,  injecting  narrow  veins  of 
rock  into  the  body  of  the  core. 

It  is  to  be  remembered  that  the  erosion  which  has  thus  laid  bare  a  basal 
section  of  so  great  a  volcano  was  accomplished  after  the  accumulation  of 
this  vast  pile  of  Miocene  ejections  and  before  the  extrusion  of  the  immense 
Hood  of  rhyolitic  lava  forming  the  jdateau  of  the  Yellowstone  Park.  In 
the  region  of  Electric  Peak  and  Sepulchre  Mountain  there  are  evidences  of 
orographic  movement  accompanying  this  period  of  denudation,  shown  in  the 
profound  faulting  which  cut  in  two  that  audesitic  volcano ;  but  the  region 
of  Crandall  Basin  seems  to  have  escaped  serious  orographic  disturbance. 

PETROGRAPHY  OF  THE  ROCKS  OF  THE  DISTRICT. 

The  extn.^sive  rocks  of  the  volcano  of  Crandall  Basin  are  in  the  main 
the  same  as  those  found  in  various  parts  of  the  Yellowstone  Park,  those 
of  Sepulchre  jMountain  having  been  described  in  Chapter  III.  It  will  not 
be  necessary  to  repeat  in  detail  the  characteristics  of  most  of  the  I'ocks,  but 
the  petrographical  features  that  are  distinctive  of  this  volcano  will  ])e  fully 
described. 

EARLY  ACID  BRECCIA. 

The  early  acid  breccia  consists  of  small  fragments  and  dust  of 
hornblende-mica-andesite,  hornblende-andesite,  and  hornblende-pyroxene- 
andesite.  The  microscopical  characters  are  quite  normal.  The  andesites  are 
partly  holocrystalline  and  partly  glassy.  The  structures  of  the  groundmass 
are  typical  of  andesites,  and  the  phenocrysts  of  plagioclase,  hornblende, 
biotite,  hypersthene,  and  augite  exhibit  the  usual  characteristics.  The  color 
of  the  hornblende  varies  from  reddish  brown  and  brown  to  brownish  green, 
green,  and  bluish  green,  and  is  often  strongly  pleochroic.  In  one  occur- 
rence there  is  a  little  quartz  in  microscopic  ^phenocrysts.  There  is  a  consid- 
erable range  of  composition,  and  the  rocks  grade  into  varieties  which  are 
like  the  more  siliceous  andesites  of  the  overlying  breccias,  a  small  portion  of 
which  is  hornblende-pyroxene-andesite.  They  also  appear  to  pass  upward 
into  the  basic  breccias  in  certain  localities,  though  in  others  there  are  evi- 
dences of  an  intermission  accompanied  by  erosion. 


288     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

BASIC  BRECCIA  AND   LAVA  FLOWS. 

The  basic  breccia  is,  with  some  exceptions,  dark  colored,  gray,  and 
reddish  brown,  and  is  as  a  whole  basaltic.  Variations  in  mineral  composi- 
tion occur  within  narrow  limits,  and  are  most  noticeable  in  the  amounts 
of  olivine  and  hypersthene.  All  proportions  ot  olivine  exists.  According 
to  the  preponderance  of  one  or  the  other  the  rocks  may  be  classed  as 
basalts  or  pyroxene-andesites,  though  their  other  characters  remain  much 
the  same.  Variovis  modifications  of  the  rock  are  mingled  in  the  breccias, 
but  to  a  different  extent  in  different  localities.  In  some  cases  the  material  is 
very  uniform  in  its  habit.  Of  the  specimens  collected  two-thirds  are  liasalt. 
Hornblende-bearing  varieties  are  extremely  rare,  and  occur  in  the  neighbor- 
hood of  the  early  acid  breccia. 

In  most  instances  the  rocks  exhibit  no  lai'ge  phenocrysts,  but  carry  a 
nmltitude  of  minute  tabular  feldspars  and  somewhat  larger  pyroxenes,  with 
more  or  less  olivine.  There  are  modifications  of  the  rock — which  are  more 
numerous  within  the  region  of  chaotic  breccia — that  carry  tabular  feldspars 
5  to  8  mm.  long,  and  still  others  with  the  same  form  of  feldspar  30.  mm. 
long,  the  large  feldspars  being  crowded  with  inclusions.  The  rocks  are 
very  generally  vesicular  and  scoriaceous,  but  a  part  are  dense  and  compact. 
In  thin  sections  the  groundmass  possesses  an  andesitic  habit,  and  consists 
of  brown  and  red  globulitic  g-lass,  which  is  occasionally  colorless,  with 
microlites  of  feldspar  and  grains  of  pyroxene  and  magnetite.  In  some 
instances  it  is  opaque  through  an  excess  of  iron  oxide,  and  in  other  cases  it 
is  holocrystalliue.  The  phenocrysts  are  plagioclase,  augite,  magnetite,  and 
more  or  less  hypersthene  and  olivine.  The  microscopical  characters  of 
these  minerals  are  the  same  as  in  other  occurrences  in  this  region.  A  basalt 
with  andesitic  habit  from  Saddle  Mountain  is  shown  in  PI.  XXXIV,  fig.  3. 

Hypersthene  is  more  abundant  as  olivine  is  less  so,  and  is  absent  from 
the  rocks  with  much  olivine.  Occasionally  hypersthene  is  surx'ounded  by 
augite  with  parallel  orientation.  In  some  cases  augite  is  brown  at  the 
center,  with  a  zonal  structure.  In  most  cases  it  is  pale  green.  The  olivine 
is  unaltered  in  many  occurrences  and  completely  serpentinized  in  others. 
In  general  the  rocks  are  very  fresh,  with  slight  indications  of  weathering, 
and  only  an  occasional  development  of  zeolites  An  unusual  and  interesting 
variety  of  the  latter  mineral  was  collected  and  investigated  by  Prof.  L.  V. 


BASALT  FLOWS.  239 

I'irssou,  who  determined  it  to  be  mordeiiite.'  Very  j^lassy  t'onns  of  rock 
are  found  in  the  breccia  on  the  ridge  south  of  Indian  Peak.  Some  are 
fragments  of  black  glass  with  a  few  small  phenocrysts  of  tabular  feldspar. 
Others  are  gray  and  exhibit  spheroidal  cracking,  and  constitute  masses  of 
considerable  size.  The  black  fragments  are  basalt-andesite  glass,  which  is 
dark  brown  and  almost  o]>aqne  in  thin  section,  with  few  scattered  microlites. 
In  some  sections  the  glass  is  mottled  and  streaked  with  light  brown.  The 
microlites  consist  of  feldspar  needles  and  grains  of  magnetite  surrounded 
by  halos  of  colorless  glass,  besides  a  few  small  augite  crystals  and  serpen- 
tinized  olivines.  There  are  somewhat  larger  plagioclases  with  inclusions  of 
brown  glass.  The  chemical  analysis  of  this  rock  (analysis  6  on  page  260) 
proves  it  to  be  intermediate  between  basalt  and  andesite.  The  gray  glassy 
varieties  belong  to  pyroxene-andesite.  In  thin  section  this  glass  is  colorless 
to  light  brown,  Avith  small  crystals  of  plagioclase  and  fewer  of  magnetite, 
augite,  and  hypersthene,  and  in  rare  instances  hornblende. 

The  variety  of  basalt  with  feldspar  phenocrysts  30  mm.  long  is  char- 
acterized by  a  slightly  different  microstructure.  The  groundmass  consists 
of  tabular  feldspars,  composed  of  kernels  of  labradorite  with  margin  of 
orthoclase,  besides  smaller  augites  and  magnetite,  through  which  are  scat- 
tered larger  microscopic  crystals  of  the  same  minerals,  with  patches  of 
serpentine.  The  phenocrysts  are  small  megascopic  labradorite,  augite, 
decomposed  serpentine  and  magnetite,  besides  extremely  large  tabular 
labradorite.  Avith  abundant  inclusions  of  glass  or  groundmass.  These  basalts 
are  intermediate  between  normal  basalts  and  the  shoshonite  described  in 
Chapter  IX. 

BASALT  FLOWS. 

The  lava  flows  intercalated  in  the  breccias  are  all  basalt,  with  variable 
amounts  of  olivine,  judging  from  the  thirty  specimens  of  them  which  were 
collected.  None  proved  to  be  andesite.  In  general  they  come  from  higher 
parts  of  the  volcano,  and  represent  later  phases  of  its  eruption.  But  some 
of  them  occur  among  the  earlier  products,  and  while  it  may  be  said  that 
the  basalts  formed  almost  the  whole  of  the  later  outflows  of  the  volcano, 
and  that  the  magma  became  more  basic  iip  to  this  period,  it  must  not  be 
forgotten  that  the  eruptions  varied  constantly  within  narrow  limits,  and  that 

'  On  mordenite :  Am.  Jour.  Sci.,  3d  series,  Vol.  XL,  Sept.  1890,  pp.  282-237. 


240  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

ill  the  earlier  history  of  the  volcano  this  variation  was  within  such  a  part  of 
the  chemical  scale  of  variation  that  the  resulting  rocks  might  be  called 
andesites  or  basalts,  but  that  this  difterence  of  name  corresponds  to  no 
greater  difference  in  composition  than  that  between  the  varieties  of  basalt 
of  the  later  period.  It  is  also  probable  that  flows  of  pyroxene-andesite 
occur  among  the  lava  streams,  but  that  they  were  not  distinguished  in  the 
field. 

The  greater  part  of  the  basalt  flows  are  andesitic  in  habit — that  is,  in 
microstructure — and  are  like  the  basalts  forming  the  breccias.  None  of  them 
are  ophitic.  The  groundmass  is  in  most  cases  glassy;  in  others,  holocrystal- 
line.  Some  of  them  carry  large  phenocrysts  of  feldspar  and  resemble  the 
same  variety  of  breccia  in  microstructure.  Some  contain  a  little  orthoclase  in 
the  groundmass,  and  are  intermediate  between  normal  basalt  and  shoshonite. 

INTRUSIVE    ROCKS. 
OUTLVlNe    DIKES. 

As  already  pointed  out,  the  dikes  belong  to  several  converging  groups, 
the  largest  of  which  centers  in  the  gabbro  core  and  a  smaller  one  in  a  focus  a 
few  miles  east,  while  a  great  number  of  dikes  in  the  southern  part  of  the 
district  belong  to  an  outlying  volcanic  center  situated  near  the  headwaters 
of  Stinkingwater  River. 

The  rocks  constituting  these  dikes  exhibit  more  variation  than  the  brec- 
cias, though  the  majority  of  them  are  like  the  breccias  in  composition  and 
habit,  being  basalt.  But  toward  the  end  of  the  period  of  volcanic  activity, 
as  we  learn  from  the  structure  of  the  granular  core,  the  composition  of  the 
magma  became  more  and  more  siliceous,  and  the  volume  of  the  lava 
erupted,  or  the  size  of  the  fissures  from  which  we  estimate  this  volume, 
became  smaller.  At  the  same  time  we  learn  from  certain  dikes  that  peculiar 
phases  of  the  magma  made  their  appearance,  the  rocks  of  which  deserve 
special  consideration.  It  is  to  be  remarked  that  while  the  most  siliceous 
modifications  of  the  magma  occur  within  the  core,  the  most  basic  phases  of 
it  are  found  at  considerable  distances  from  the  center,  with  one  exception. 
This  accords  with  the  idea  that  the  more  siliceous  products  of  differentiation 
will  occur  near  the  center  of  the  reservoir  in  which  differentiation  takes  place, 
presumabl}'  beneath  the  crater  of  a  volcano,  while  the  less  siliceous  products 


BASALT  DIKES.  241 

will  occur  near  the  niarjicin  of  the  reservoir,  away  from  the  crater.'  More- 
over, it  is  to  be  noted  that  while  many  of  the  exceptional  modifications  of 
the  magma  appear  to  be  connected  with  the  center  of  eruption  in  Crandall 
Basin,  they  are  more  numerous  in  the  southern  district,  about  the  head  of 
Stinkingwater  River.  In  describing  the  intrusive  rocks  we  shall  com- 
mence with  those  which  resemble  most  closely  the  breccias  and  surface 
flows. 

Basalts. — The  basalts  of  the  dikes  exhibit  the  same  megascopical  habit 
and  variability  as  those  of  the  breccias.  Part  of  them  have  a  multitude  of 
small  pheliocrysts  of  tabular  labradorite  and  augite,  and  part  carry  very 
large  labradorites.  They  appear  to  be  the  same  varieties  of  magma  which 
have  cooled  in  dikes,  and  consequently  possess  a  slightly  different  ground- 
mass.  In  a  large  number  of  cases  the  groundmass  consists  of  lath-shaped 
labradorite  and  crystals  of  augite  and  magnetite  in  a  small  amount  of 
microlitic  base.  The  augite  is  occasionally  slightly  pleochroic.  The  pheno- 
crysts  are  tabular  labradorite,  augite,  and  olivine,  with  magnetite  and  stout 
colorless  apatite.  In  a  number  of  dikes  the  groundmass  contains  orthoclase 
as  margins  around  the  microlites  of  labradorite.  One  of  the  most  pro- 
nounced of  these  varieties  (1325)  forms  a  dike  on  the  ridge  south  of  Closed 
Creek.  Its  chemical  composition  is  given  by  the  third  analysis  on  page  260. 
It  is  closely  related  to  shoshonite,  as  pointed  out  in  Chapter  IX.  Others 
contain  less  orthoclase  and  are  intermediate  between  shoshonite  and  normal 
basalt.  To  this  variety  belong  most  of  the  dikes  at  the  head  of  Miller 
Creek  and  those  cutting  the  summit  of  Saddle  Mountain. 

In  some  cases  the  groundmass  contains  microlitic  and  globulitic  glass 
base;  in  others  it  is  holocrystalline.  A  glassy  basalt  from  Hunter  Peak 
contains  microlitic  needles  of  feldspar,  slightly  curved,  and  magnetite  grains 
pointed  at  the  corners,  besides  augite  microlites  with  magnetites  attached. 
In  some  occurrences  these  needles  are  coated  with  magnetite  and  resemble 
thin  black  lines. 

It  is  often  observed  that  the  face  of  a  dike  along  the  plane  of  contact 
is  glassy,  while  the  center  is  holocrystalline.  In  one  instance  this  contact 
facies  consists  of  almost  opaque  brown  globulitic  glass  with  much  iron 
oxide  in  minute  rods,  and  thin  feldspar  needles  with  long  forked  longitudinal 
sections  shaped  like  an  H,  the  groundmass  extending  to  near  the  middle  of 

'  L.  V.  Pirsson,  ComplemeDtary  rocks  ami  railiatinj;  dikes :  Am.  Jour.  Sci.,  3d  series,  Vol.  L,  1893,  p.  120. 
MON  XXXII,  PT  II 10 


242  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  crystal.  Cross  sections  are  square,  with  large  square  inclusions  of 
groundmass.  Ilmenite  occurs  in  many  of  the  rocks  in  rod-like  crystals,  and 
a  small  amount  of  serpentine  is  present  in  most  of  the  groundmasses. 

Olivine  is  decomposed  to  serpentine  in  most  instances,  and  originally 
formed  small  as  well  as  large  crystals.  In  one  of  the  fresher  rocks  the 
groundmass  contains  many  small  olivines,  which  are  probably  the  mineral 
from  which  the  serpentine  in  the  groundmass  of  the  more  altered  rocks  was 
derived.  As  a  whole,  the  basaltic  dikes  are  not  so  fresh  as  the  breccias 
surrounding  them,  although  they  are  the  younger  rocks.  Those  with  large 
tabular  feldspars  acquire  a  very  characteristic  appeai-ance  through  the 
whitening  of  these  crystals,  which  are  strongly  contrasted  with  the  dark 
dense  groundmass.  The  large  dark- colored  augites  are  also  distinctly 
noticeable. 

Gabbro-   and   diorite-porphyries   and   andesites. The     rOCks     wllicll     WOuld     be      plaCed 

under  this  division  in  consequence  of  a  microscopical  examination  jjrobably 
belong  quite  as  closely  to  the  basalts.  With  one  exception  they  all  occur 
in  close  proximity  to  the  granular  core,  and  some  of  them  are  included  in 
it.  The  one  exception  is  a  narrow  dike  of  pyroxene-andesite,  the  ground- 
mass  of  which  is  filled  with  serpentine,  indicating  the  former  presence  of  a 
magnesian  mineral,  possibly  olivine. 

The  rocks  of  this  division  exhibit  all  of  the  modiiications  of  mega- 
scopical  habit  shown  by  those  just  described,  and  resemble  them  closely  in 
hand  specimens.  They  are,  however,  more  crystalline  and  present  micro- 
structures  both  distinctive  and  characteristic,  which  are  related  to  differences 
in  mhieral  composition.  A  few  of  the  andesitic  dikes  which  cut  the  summit 
of  the  plateau  west  of  the  core  are  very  fine  grained  and  are  considerably 
altered,  and  contain  chlorite  and  epidote. 

The  absence  of  olivine  from  most  of  the  more  crystalline  forms  of 
these  rocks  appears  to  be  due  to  the  causes  which  influenced  the  crystalli- 
zation of  the  rocks  and  not  to  their  chemical  composition,  for  the  hand 
specimens  in  some  cases  show  what  seem  to  be  decomposed  crystals  of 
olivine,  which  in  thin  section  are  found  to  be  paramorphs  after  this  mineral. 

This  group  of  rocks  includes  the  intrusive  sheets  on  top  of  Hurricane 
Mesa  and  certain  dikes.  In  the  immediate  neighborhood  of  the  core  and 
within  the  zone  of  indurated  breccia  the  massive  sheet  of  intrusive  rock 
appears  dense  and  aphanitic  (1359, 1361,  1369),  and  carries  abimdant  tabu- 


GABBRO  AND  DIOUlTE-rOKPUYRIES.  243 

lar  feldspars  5  mm.  lon<i^  and  laro^e  augites.  In  tliin  section  it  is  holociystal- 
line,  the  groundniass  consisting-  of  short  tabidar  and  indistinctly  outlined 
plagioclase,  with  low  double  refraction  and  moderately  low  extinction  angles, 
besides  considerable  magnetite  and  minute  gi-ains  of  epidote  and  chlorite, 
which  appear  to  replace  pyroxene.  The  degree  of  crystallization,  compared 
with  the  rocks  of  Electric  Peak,  varies  from  grade  8  to  16.  Throughout 
the  description  of  the  more  crystalline  rocks  of  this  district  it  has  been 
found  convenient  to  refer  to  the  grades  of  crystallization  established  for  the 
series  of  rocks  at  Electric  Peak  and  Sepulchre  Mountain  (Table  XVII, 
Chapter  III).  This  serves  to  correlate  the  various  phases  of  crystalliza- 
tion of  the  rocks  of  Crandall  Basin,  not  only  with  one  another,  but  also 
with  those  of  the  district  just  named. 

In  the  more  crystalline  forms  of  this  rock  the  feldspars  are  more  lath- 
shaped,  magnetite  is  abundant,  and  the  ferromagnesian  minerals  are  pale- 
green  augite,  some  hypersthene,  a  little  biotite,  pale-green  amphibole,  and 
a  little  quartz.  Apatite  occurs  in  stout  crystals.  The  phenocrysts  are 
large,  and  are  mostly  labradorite  in  idiomorphic  crystals  and  augite  in  less 
regularly  defined  ones.  The  labradorite  is  especially  noticeable  on  account 
of  clouds  of  dust-like  and  rod-shaped  inclusions,  Avhich  give  it  a  brown- 
ish tint,  besides  clusters  and  rows  of  rounded  grains  of  magnetite,  augite, 
and  biotite.  Immediately  surrounding  these  larger  inclusions  is  a  zone  of 
feldsiDar  substance,  free  from  the  cloud  of  minute  inclusions,  indicating  that 
the  material  composing  the  minute  inclusions  is  the  same  as  that  forming 
the  larger  ones,  which  has  been  concentrated  in  certain  spots  into  the 
minerals  mentioned.  This  phenomenon  appears  in  perfectly  fresh  feldspars 
which  exhibit  no  cracks  or  signs  of  alteration,  and  in  those  which  are 
greatly  cracked  there  is  no  relation  between  the  position  of  the  cracks  and 
the  distribution  of  the  inclusions,  which  frequently  lie  in  crystallographic 
zones.  They  are  unquestionably  primary  microlitic  bodies,  inclosed  at  the 
time  of  the  crystallization  of  the  feldspar,  and  are  not  of  secondary  origin, 
like  those  described  by  Judd  in  the  minerals  of  cei-tain  peridotites.^  In  the 
unaltered  rock  the  augite  is  fresh,  and  biotite  appears  as  a  primary  crystal- 
lization, but  not  in  phenocrysts.  The  amphibole  is  secondary  and 
accompanies  the  uralitization  of  the  augite.     There  are  patches  of  irregularly 

'J.  W.  Judd,  On  the  Tertiary  and  older  peridotites  of  Scotland:  Quart.  Jour.  Geol.  Soc,  Aug. 
1885,  pp.  371-389;  also.  On  the  relations  between  the  Bolution  planes  of  crystals  and  those  of  secondary 
twinning,  etc. :  Min.  Mag.,  Vol.  VII,  pp.  81-92. 


244     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

oriented  augite,  magnetite,  and  biotite,  which  correspond  to  more  definite 
paramorphs  after  ohvine  in  some  of  the  other  rocks. 

Similar  rocks  occur  in  dikes  within  .he  margin  of  the  core.  They  ai-e 
shghtly  coarser  grained.  One  (1378)  forms  a  4-foot  dike  near  the  base  of 
the  pinnacled  spur  on  the  west,  and  a  still  coarser-grained  form  (1418) 
occurs  in  a  12-foot  dike  on  the  same  spur,  somewhat  nearer  the  center  of 
the  core;  its  grade  of  crystallization  is  about  20.  The  microstructure 
becomes  more  pronounced  as  the  constituent  crystals  are  larger  and  more 
distinct.  The  labradorite  has  the  same  kinds  of  inclusions,  but  the  outlines 
are  in  part  serrated  by  the  interference  of  adjacent  grains  in  the  groundmass. 
The  rusted  paramorphs  have  outlines  more  characteristic  of  olivine.  The 
massive  intrusive  sheet  on  the  eastern  side  of  the  core  (1372)  is  like  the  last 
in  composition  and  mici'ostnicture,  but  there  is  a  little  more  biotite.  There 
is  some  orthoclase  as  margins  around  prisms  of  labradorite,  precisely  like 
the  occurrence  of  orthoclase  in  shoshonite,  but  its  amount  is  small.  The 
chemical  anal3^sis,  No.  II  on  page  261,  shows  a  relatively  high  percent- 
age of  potash,  and  the  rock  is  closely  related  to  shoshonite,  .but  is  a  little 
higher  in  lime  and  magnesia  and  a  little  lower  in  alkalies.  It  is  almost  a 
shoshonite-porphyry  or  monzonite-porphyry.  The  two  rocks  are  quite  fresh, 
and  exhibit  no  signs  of.  crushing  or  other  indications  of  alteration,  the  large 
feldspars  being  glass}^  and  not  cracked.  The  microstructure  of  1372  is 
shown  in  PI.  XXXVII,  fig.  2.  This  rock  is  pyroxene-diorite-porphyry 
approaching  monzonite-porphyry. 

Another  variet}*  of  massive  intrusive  rock  is  exposed  at  the  bottom  of 
the  southwest  spin-  of  the  core  (1377,  1379,  1383).  It  appears  to  be  a  dense 
aplianitic  form  of  the  gabbro,  and  is  probably  an  apophysis  or  the  margin 
of  the  core.  It  is  a  basalt- porphyry.  The  poi'phyritical  crystals  of  augite 
rise  above  the  gi'oundmass  of  the  rock  on  weathered  and  fractured  surfaces. 
It  is  to  be  borne  in  mind  that  the  chemical  composition  of  this  rock  (analysis 
4  on  page  260)  is  the  same  as  that  of  some  of  the  basalts  of  the  district, 
so  that  the  rock  is  a  special  phase  of  crystallization  of  this  magma. 

In  thin  section  the  finest-grained  forms  have  an  andesitic  structure  in 
the  groundmass.  A  slightly  more  crystalline  variety  is  still  andesitic,  but 
consists  of  lath-shaped  and  rectangular  plagioclase  in  a  matrix  of  grains  of 
feldspar,  augite,  hypersthene,  and  magnetite,  besides  minute  crystals  of 
light-brown  biotite.     In  places  the  feiTomagnesian  minerals  preponderate. 


GABBKO  AND  DIOKITE-I'ORPHYKIES.  245 

In  some  cases  the  small  plagioclases  are  clouded  brown  in  the  same  manner 
as  the  larger  ones  already  described.  The  jjhenocrysts  are  light-green 
augite  and  paramorphs  after  (?)  olivine.  The  augite  j)henocrysts  contain 
nnich  magnetite  in  minute  grains,  which  are  sometimes  arranged  zonally. 
One  of  the  thin  sections  contains  several  clusters  of  grains  of  grass-green 
augite,  slightly  pleochroic,  which  form  borders  around  other  minerals.  In 
one  instance  they  inclose  grains  of  quartz,  calcite,  and  pale-yellow  garnet, 
the  grains  of  garnet  being  mingled  with  those  of  augite. 

A  question  now  presents  itself  which  is  interesting  because  of  its 
importance  in  discussions  regarding  systems  of  classification  of  igneous 
rocks,  all  of  which  systems  are  designed  to  be  as  natural  as  possible.  The 
question  is.  Which  of  two  lines  of  relationship  is  to  be  followed  in  a 
particular  instance?  We  have  described  the  subaerial  breccias  and  lava 
flows  together  in  a  group,  and  then  given  with  a  description  of  the 
dikes  and  sheets  of  intrusive  rocks  of  similar  character.  Shall  we  continue 
the  description  of  the  remainder  of  the  rocks  occurring  in  dikes,  which 
exhibit  a  wider  range  of  variation  than  those  just  described,  or  shall  we 
follow  the  dikes  continuously  a  few  feet  farther  into  the  granular  core  and 
take  up  the  consideration  of  their  more  crystalline  forms?  In  the  first 
instance  we  have  a  natural  grouping  based  on  similarity  of  occurrence  and 
of  outward  petrographical  habit — that  is,  of  general  aspect  derived  from 
their  phase  of  crystallization,  which  is  combined  with  variations  in  mineral 
and  chemical  composition.  In  the  second  case  we  have  a  natural  connec- 
tion based  on  actual  continuity  of  mass,  and  when  this  is  not  directly 
traceable  in  the  field  the  connection  is  one  of  identity  of  chemical  composi- 
tion. With  these  constant  factors  are  combined  the  variable  ones  expressed 
by  differences  in  mineral  composition  and  in  degree  of  crystallization.  In 
nature  these  relationships  either  exist  as  accomplished  facts  in  regions  of 
extinct  volcanoes  or  they  are  in  process  of  development  in  regions  of  active 
ones.  In  the  foi'mer  they  exist,  not  in  two  groupings  such  as  we  have 
depicted,  but  as  one  great  complex  system  of  relationships,  involving  varia- 
tions in  chemical  composition  and  crystalline  structure  and  still  more 
intricate  variations  in  minei'al  composition.  While  in  regions  of  active 
vulcanism  we  may  readilj^  conceive  of  a  number  of  processes  of  rock- 
making  being  in  action  in  difi'erent  places  at  one  time,  in  the  vast  com- 
plexity of  rocks  resulting  from  the  working  out  of  these  pi'ocesses  it  is  the 


246  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

variable  characters  which  express  the  active  principles  of  vulcanism  whose 
laws  are  the  ultimate  object  of  our  investigations.  Hence  it  is  that  in  the 
treatment  of  intricate  groups  of  rocks  belonging  to  any  one  region  we  are 
constantly  confronted  by  questions  as  to  the  best  methods  of  studying  and 
of  describing  the  variability  of  the  rocks.  In  the  present  instance  it  will 
be  most  advantageous  to  proceed  with  a  consideration  of  the  development 
of  crystalhzation  in  the  core  of  the  volcano,  postponing  the  description  of 
the  remaining  dikes  in  order  to  connect  them  more  closely  with  other 
bodies  of  similar  rocks  from  different  parts  of  the  Yellowstone  Park,  which 
will  be  described  collectively  in  another  chapter  (Chapter  IX). 

GRANULAR   CORE   AND   INTERSECTING  DIKES. 

Gabbro  and  gabbro-porphyry. — Tlie  westcm  aiid  cciitral  portlous  of  the  granular 
core  have  been  explored  with  as  much  care  as  the  time  allowed,  but  the 
eastern  part  below  the  summit  of  the  plateau  was  not  visited.  The  main 
mass  consists  of  coarsely  granular  rock  intersected  by  dikes  or  veins  from 
20  feet  to  10  inches  in  width,  which  are  more  noticeable  in  the  margin  of 
the  core,  where  they  exhibit  a  radial  arrangement.  The  character  and 
composition  of  the  granular  rock  vary  to  some  extent.  It  is  a  gabbro — 
that  is,  it  consists  primarily  of  labradorite-bytownite  and  pyroxene,  with 
biotite  an4  very  little,  if  any,  hornblende,  with  some  orthoclase  and  a  little 
quartz,  and  grades  into  facies  which  are  quartz-diorite.  In  places  the 
alkalies  are  higher  tlian  in  normal  gabbro  or  diorite  and  lead  to  the  produc- 
tion of  considerable  orthoclase,  yielding  varieties  of  rock  approaching 
monzonite,  and  in  some  cases  being  monzonite.^  It  becomes  finer  grained 
toward  the  margin  of  the  core,  and  an  idea  of  its  microscopical  character- 
istics is  best  obtained  by  following  the  changes  from  fine  to  coarse  grain 
through  two  series  of  specimens  collected  for  the  purpose. 

One  series  of  nine  specimens  represents  the  modifications  which  have 
taken  place  within  a  distance  of  100  feet.  The  finest-grained  form  (1388) 
is  near  the  southwest  margin  of  the  core  on  the  southwest  spur,  at  a  spot 
225  feet  higher  up  the  slope  than  the  specimen  (1383)  already  described, 
which  was  collected  from  the  massive  exposures  and  which  has  been  called 
a  basalt-porphyry.  The  two  rocks  resemble  each  other  in  the  character  of 
their  phenocrysts,  but  the  latter  has  a  finer-grained  groundmass. 

'  Brogger,  W.  C,  Die  Eruptivgesteine  des  Kristianiagebietes:  II.  Die  Eruptionsfolge  der  tria- 
dischen  Eruptivgesteiue  bei  Predazzo  in  SUdtyrol,  CUristiania,  1895. 


GRANULAR  CORE  AND  DIKES.  247 

The  first  two  rocks  of  tlie  series  (1388,  1389)  are  yellowisli  gray  and 
crystalline,  plainly  composed  of  feldspar  and  ferroniagnesian  silicates,  partly 
biotite,  with  small  phenocrysts  of  augite.  In  thin  section  they  are  medium 
grained,  grade  23  of  Table  XVII,  Chapter  III,  and  consist  of  lath-shaped, 
and  also  short,  rounded  jjlagioclase  crystals  and  some  of  orthoclase.  The 
feldspars  are  very  fresh,  ])ut  contain  a  crowd  of  minute  crystals  of  magnetite, 
biotite,  pyroxene,  and  apatite.  There  is  a  large  amount  of  ferroniagnesian 
minerals  in  the  rock.  Tliey  are  augite  and  hypersthene  in  rounded  and 
irregidar  grains  of  variable  size,  besides  biotite  in  very  irregularly  shaped 
individuals,  and  much  magnetite.  There  are  a  few  phenocrysts  of  augite 
crowded  with  magnetite  grains  in  clouds  and  zones,  and  in  some  cases  there 
are  characteristic  rod-like  inclusions.  Magnetite,  pyroxene,  and  biotite 
frequently  occur  in  irregular  aggregations.  Olivine  is  present  in  partly 
serpentinized  individuals.  The  resemblance  of  many  of  these  character- 
istics to  those  already  described  for  some  of  the  intrusive  masses  imme- 
diately connected  with  the  core  will  be  recognized.  The  chemical 
composition  of  this  modification  of  the  rock  (analysis  1  on  page  260)  is  like 
that  of  basalt.  The  next  two  varieties  (1390,  1391)  are  coarser  grained, 
grade  27,  with  a  slight  modification  of  the  previous  structure,  caused  by 
the  presence  of  abundant  phenocrysts  of  tabular  labradorite  in  a  ground- 
mass  with  the  structure  just  described.  In  places  there  is  a  poikilitic 
structure,  occasioned  by  small  rounded  plagioclases  and  pyroxenes  being 
inclosed  in  a  broad  hidividual  of  unstriated  feldspar,  which  is  undoubtedly 
ortlioclase.  These  poikilitic  feldspars  act  as  the  cement  for  the  idiomorphic 
jjlagioclases  and  often  equal  the  feldspar  phenocrysts  in  size.  Tliere  are 
traces  of  a  graphic  intergrowth  of  quartz  in  orthoclase.  The  rock  is  very 
fresh  and  unaltered.  There  is  much  hypersthene,  augite,  and  magnetite, 
some  biotite,  and  a  little  green  hornblende.  The  labradorite  is  very  clear 
and  fresh,  with  some  transparent  rectangular  inclusions  resembling  glass, 
and  in  some  cases  with  many  inclusions  of  mici'ocrystals  of  pyroxene, 
biotite,  and  magnetite.  Tlie  augite  has  a  purplish  tone,  is  light  colored, 
with  many  rod-  or  needle-like  inclusions  in  the  larger  individuals.  Besides 
the  prismatic  cleavage  there  is  distinct  jjinacoidal  cleavage.  The  hyper- 
sthene is  light  colored,  with  the  usual  pleochroism.  It  is  occasionally  in 
long  prisms,  with  the  color  stronger  along  the  margin.  Some  of  the  crystals 
have  needle-like  inclu.sions.     In  both  pyroxenes  these  inclusions  exhibit  no 


248  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

connection  with  the  cracks  in  the  crystals,  and  are  undoubtedly  primary. 
The  biotite  frequently  suiTounds  mag-netite  and  is  attached  to  it  and  the 
pyroxene.  In  one  of  the  rocks  there  is  a  moderate  amount  of  compact 
green  hornblende,  which  forms  borders  and  intergrowths  with  pyroxene  in 
exactly  the  same  manner  as  in  the  diorite  of  Electi'ic  Peak.  In  one  of  these. 
forms  of  the  rock  one  augite  has,  besides  the  rod-like  inclusions  character- 
istic of  this  occurrence,  others  which  are  immediately  connected  with  distinct 
cracks  and  are  undoubtedly  secondary.  This  was  the  only  instance  of  the 
kind  noticed  in  these  remarkably  fresh  rocks. 

The  next  two  modifications  of  the  rock  (1392,  1393)  are  still  coarser 
grained,  but  have  the  same  microstructure.  Tlie  outline  of  the  porphyritical 
feldspars  is  lost  in  an  irregular  interlocking  of  adjacent  crystals.  The 
poikilitic  orthoclase  is  more  distinct.  In  the  next  two  phases  of  the  rock 
(1394,  1395)  the  grain  is  still  coarser,  resembling  that  of  a  fine-grained 
granite.  They  have  a  saccharoidal  texture  in  hand  specimens,  which  is 
characteristic  of  the  greater  ilumber  of  all  of  the  rocks  of  the  core.  When 
broken  they  appear  loosely  coherent,  tlie  crystals  parting  along  faces  and 
cleavage  planes  rather  than  in  smooth  j)lanes  across  the  rock.  The  micro- 
structure  of  these  forms  of  the  rock  resembles  that  of  the  preceding,  without 
the  porphyritic  development.  The  feldspathic  minerals  are  in  excess  of  the 
ferromagnesian.  Tlie  largest-sized  individuals  of  feldspar  are  the  poikilitic 
orthoclases,  but  the  lath-shaped  plagioclase  is  far  more  abundant.  Some 
individuals  of  orthoclase  have  a  marked  micrographic  and  plumose  arrange- 
ment of  quartz  inclusions,  associated  with  which  are  long  hair-like  needles, 
which  in  places  pass  into  lines  of  black  dots.  They  also  contain  some 
microcrystals  of  mica.  The  ferromagnesian  minerals  are  partly  idiomorphic 
and  consist  of  augite,  hypersthene,  green  hornblende,  and  biotite  in  about 
equal  proportions.  It  is  to  be  remarked  that  in  these  gabbros  the  color 
of  the  hornblende  is  generally  stronger  and  purer  green  than  in  the 
diorite  of  Electric  Peak.  The  crystals  of  apatite  and  zircon  are  noticeably 
larger  in  these  modifications  of  the  rock  than  in  the  finer-grained  ones.  In 
specimen  1395  biotite  occurs  in  large  interrupted  patches.  This  is  charac- 
teristic of  the  coarsest-grained  member  of  the  series  (1396),  which  is  a  gray 
granular  rock  that  is  exposed  in  large  rounded  masses,  weathering  into  sand 
and  resembling  a  crumbling  gi-anite  supei-ficially.  In  thin  section  it  exhibits 
the  same  microstructure  as  the  previous  variety,  but  is  still  coarser,  being 


OUTIIOCLASE-GABBUO.  249 

grade  43,  nearly  that  of  the  coarsest  rock  found  at  Electric  Peak.  The 
minerals  are  the  same  as  in  the  last  variety,  but  the  ferromagnesian  silicates 
are  more  abundant,  especially  biotite.  The  pyroxenes  do  not  carry  many 
microlitic  inclusions.  The  raicrographic  structui-e  in  scattered  patches  is 
pronounced.  Olivine  is  absent  from  the  more  crystalline  members  of  this 
series  of  specimens,  and  the  chemical  analysis  (No.  8  on  page  260)  shows  that 
the  most  crystalline  portion  of  the  rock  is  more  siliceous  and  feldspathic 
than  that  nearer  the  margin  of  the  core.  These  rocks  are  orthoclase-gabbro 
and  orthoclase-gabbro-diorite,  approaching  monzonite. 

Along  the  crest  of  the  spur  towai'd  the  northwest  the  gabbro  becomes 
less  coarse  and  more  porphyritic,  with  abundant  tabular  feldspars  (1397), 
and  assumes  the  phase  of  crystallization  represented  by  1392,  already 
described. 

Another  series  of  specimens  represents  the  gabbro  just  south  of  the 
lake  at  the  head  of  the  west  gulch.  The  coarsest- grained  variety  (1430, 
1431),  near  the  outlet  of  the  lake,  is  dark  colored  and  granular,  but  not 
saccharoidal.  It  is  like  1395,  the  coarsest-grained  form  in  the  series  first 
described,  in  degree  of  crystallization  and  microstructure,  but  contains  more 
ferromagnesian  silicates,  and  its  chemical  analysis  (No.  5  on  page  260) 
places  it  between  the  extremes  of  the  other  series.  There  is  much  augite 
with  pinacoidal  cleavage  and  characteristic  needle-like  inclusions,  and  less 
hypersthene,  but  numerous  serpentinized  olivines.  There  is  considerable 
biotite  and  magnetite,  a  little  orthoclase,  and  very  little  quartz.  Its  micro- 
structure  is  shown  in  PI.  XXXIII,  fig.  1. 

The  finest-grained  member  of  this  series  is  porphyritic  and  medium 
grained.  The  plagioclases  are  dusted  with  black  dots  and  rods,  the  margin 
of  the  crystals  and  the  smaller  grains  being  free  from  them.  The  dots 
appear  to  be  magnetite  in  large  part,  for  when  recognizable  grains  of  mag- 
netite occur  in  the  feldspar  they  are  surrounded  by  halos  of  clear  feldspar 
substance. 

Slightly  different  modifications  of  the  gabbro  occur  in  various  parts  of 
the  core,  some  of  which  have  been  analyzed  chemically,  and  should  there- 
fore be  described  in  more  detail  than  would  otherwise  be  necessary,  in 
order  that  the  analyses  may  gain  greater  significance.  The  gabbro  becomes 
still  coarser  grained  down  the  west  gulch,  and  a  short  distance  below  the 
lake  is  quite  micaceous  (1412).     This  rock  and  a  large  body  of  gabbro- 


250  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

diorite  (1399)  on  the  southwestern  spur  have  the  same  degree  of  crystalli- 
zation and  the  same  characteristics.  The  microstructure  is  like  that  of  the 
coarsest  variety  already  described.  The  essential  feldspar  is  labradorite  with 
a  small  amount  of  orthoclase  and  little  micrographic  quartz.  There  are  also 
allotriomorphic  grains  of  quartz,  against  which  the  orthoclase  is  idiomorphic. 
There  is  much  hypersthene,  augite,  biotite,  and  magnetite,  with  some  pri- 
mary green  hornblende.  The  hypersthene  in  certain  sections  exhibits  a 
very  fine  microscopic  lamination,  produced  by  the  parallel  intergrowth  of 
monoclinic  and  orthorhombic  pyroxene,  as  the  optical  behavior  proves. 
This  lamination  is  found  throughout  the  hypersthene  of  this  gabbro,  but  is 
recognizable  only  in  certain  sections  and  may  be  easily  overlooked.  The 
pyroxenes  have  the  characteristic  inclusions  and  pinacoidal  cleavage. 
Apatite  and  zircon  occur  in  comparatively  large  crystals.  The  chemical 
composition  of  this  rock,  shown  in  analysis  7  on  page  260,  is  like  that  of 
1396,  No.  8  of  the  same  table. 

The  lowest  exposure  of  gabbro  in  the  west  gulch  is  about  1,000  feet  lower 
than  the  lake.  It  is  compact  (1437)  and  dark  colored,  and  is  like  that  near 
the  outlet  of  the  lake,  but  is  coarser  grained,  being  higher  than  the  highest 
grade  of  crystallization  found  at  Electric  Peak.  One  of  the  coarsest-grained 
varieties  (1411)  occurs  near  the  lake  (PI.  XXXIII,  fig.  2).  It  is  once  and 
a  half  as  coarse  as  the  most  crystalline  diorite  at  Electric  Peak;  and  on 
the  crest  of  the  west  spur,  at  about  10,000  feet  altitude,  a  variety  (1436) 
is  found  which  is  twice  as  coarse  grained  as  that  at  Electric  Peak.  The 
feldsiiai's  are  from  2  to  3  nun.  long.  The  structure  is  like  that  Jast  described, 
but  there  is  more  feldspar,  and  biotite  and  hornblende  predominate  over 
the  pyroxene  and  magnetite.  By  its  mineral  composition  as  well  as  its 
chemical  (analysis  9  on  page  261)  it  is  shown  to  be  a  diorite  facies  of  the 
gabbro.  In  some  parts  of  the  core  the  dark-colored  gabbro  carries  small 
light-colored  masses,  which  are  highly  feldspathic. 

In  this  connection  may  be  described  a  remarkable  variety  of  crystalline 
rock  which  does  not  occur  within  the  gabbro  core,  but  is  found  on  the 
northeastern  spur  of  Hurricane  Mesa,  near  the  center  toward  which  the 
second  group  of  dikes  converge.  It  is  a  special  phase  of  crystallization  of 
the  magma,  whose  chemical  composition  (analysis  10  on  page  261)  corre- 
sponds to  certain  diontic  facies  of  the  gabbro  in  the  core.  The  rock  (1442) 
is  compact  and  fine  grained,  with  a  crystalline  luster  and  brilliant  reflections 


U.  S.  QEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.  XXXIII 


(A)  »    13 


( B)  X    12 


(Cj    <■    12 


(D)  X    13 


PHOTOMICROGRAPHS    OF    GABBRO,    DIORITE,    AND    GRANITIC    APLITE 


THE  MELIOTYP£  PRINTING  CO..  BOSTON 


U.  8.  OeOLOQICAL   SURVEY 


MONOGRAPH    XXXII     PART   II     Pt.  XXXIV 


(Cj  X  7a 


(D)  X   28 


PHOTOMICROGRAPHS    OF  MONZONITE,    DIORITE,   AND    BASALT 


THE  HELIOTYPE  PRINTINQ  CO.,  BOSTON 


GABBKO.  251 

from  mottled  feldspars  3  mm.  long,  which  are  poikilitir.  There  are  no 
phenocrvsts.  Tii  tluu  section  it  consists  of  small,  stftut  idiomorphic  prisms 
of  plagioclase  which  ha\-e  the  optical  characters  of  labradorite,  besides  stout 
prisms  of  augite  and  hypersthene,  jiartly  idiomorphic,  together  with  magnetite 
and  a  very  small  amount  of  biotite.  These  minerals  are  scattered  irregu- 
larly in  broad  allotriomorphic  individuals  of  orthoclase,  which  act  as  a 
cementing  matrix,  but  do  not  equal  the  plagioclase  in  amount.  It  is  nearly 
a  monzonite.  There  is  a  very  little  quartz.  Its  structure  is  shown  in  PI. 
XXXIV,  fig.  1.  Apatite  occurs  in  stout  and  in  slender  prisms.  The 
hypersthene  is  very  slightly  altered  in  places ;  otherwise  the  rock  is 
extremely  fresh.  The  small  amount  of  biotite  is  specially  noteworthy 
when  the  chemical  composition  of  the  rock  is  compared  Avith  that  of  1396 
and  1399  (analyses  8  and  7  on  page  260),  both  of  which  are  rich  in  biotite. 

Returning  to  the  gabbro  core,  we  have  to  consider  a  number  of  intru- 
sions within  the  main  body  of  granular  gabbro  and  in  the  aphanitic 
marginal  zone  which  form  dikes  representing  finer-grained  and  porphyritic 
modifications  of  the  gabbro  magma.  The  size  and  distribution  of  the 
phenocrysts  of  feldspar  and  pyroxene  show  their  relation  to  the  rocks  of 
the  outlying  dikes  with  porphyritical  feldspars  and  pyroxene,  as  well  as  to 
those  of  the  breccias  and  flows,  while  their  microstructure  connects  them 
with  the  gabbro.  They  present  intermediate  phases  of  crj^stallization 
between  the  two,  and  if  followed  continuously  into  the  surrounding  country ' 
would  connect  the  granular  gabbro  with  the  basalt. 

Of  these  intnisions  or  dikes  one  (1398)  occurs  on  the  west  spur,  at 
8,650  feet  altitude,  cutting  the  granular  gabbro.  In  thin  section  it  consists 
of  labradorite  with  irregular  outlines  in  a  groundmass  of  rounded  crystals 
of  feldspar,  augite,  hypersthene,  and  magnetite,  with  some  biotite  and 
orthoclase  and  a  little  quartz.  The  structure  is  similar  to  that  of  1383,  but 
is  coarser  grained.  The  phenocrysts  of  labradorite,  augite,  and  hyper- 
sthene have  the  inclusions  characteristic  of  the  gabbro-porphyries. 

Another  dike  of  this  rock  (1413)  cuts  the  gabbro  near  the  outlet  of 
the  lake.  The  dike  is  6  inches  wide,  and  the  rock  is  dark  gray  and  crys- 
talline, with  the  same  microscopical  habit  as  the  one  just  described.  The 
microstructure  is  intermediate  between  the  latter  and  1388.  The  feldspars 
are  dusted  at  the  center,  the  outer  portion  carrying  many  small  crystals  of 
biotite,  which  is  specially  abundant  in  this  rock.     The  third  occurrence  is 


252     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

a  2-foot  dike  (1387)  in  the  aphanitic  zoue.  It  resembles  the  preceding 
rock  in  outward  appearance  and  has  the  same  microstructure,  but  is  coarser 
grained. 

Diorite,  quartz-mica-diorite,  and   diorite-porphyry. The       graUular      rOCk      of     thc       COre 

changes  to  a  more  siUceous  facies  on  the  southern  slope  of  the  central 
round-topped  spur.  The  structure  of  this  part  of  the  core  will  be  better 
understood  if  its  description  is  commenced  at  the  base  of  the  middle  spur, 
where  the  lowest  exposures  of  massive  rock  are  dense  and  aphanitic  and 
dark  coloi'ed,  like  the  rock  at  the  base  of  the  southwest  spur.  This  is  cut  by 
dikes  with  parallel  walls,  but  higher  up  the  slope  their  form  is  not  so  regu- 
lar and  they  widen  out  toward  the  center  of  the  core,  the  rocks  composing 
them  becoming  coarse  grained  (1419,  1420).  The  structure  of  this  part  of 
the  middle  spur  is  obscured  by  slide  rock,  so  that  any  one  body  can  not 
be  traced  far.  Higher  up  the  core  is  well  exposed  and  the  rock  is  found  to 
be  lighter  colored,  with  a  strong  resemblance  to  medium-grained  diorite. 

The  rocks  from  above  9,000  feet  (1425,  1427),  when  studied  in  thin 
section,  prove  to  be  quartzose  and  feldspathic  facies  of  the  gabbro,  with 
less  ferromagnesian  minerals,  which  have  the  same  characteristics  as  those 
in  the  gabbro  proper.  Their  degree  of  crystallization  is  about  40,  and  the 
structure  is  more  nearly  granular,  since  the  orthoclase  and  quartz  nearly 
equal  the  lime-soda  feldspar  in  amount.  They  correspond  to  Brogger's 
banatite.^  The  last-nalned  mineral  is  almost  idiomorphic  and  appears  to 
be  andesine.  There  is  no  micrographic  structure.  The  rock  at  9,300  feet 
altitude  (1425)  contains  biotite,  augite,  hypersthene,  magnetite,  and  a  little 
hornblende.  There  is  much,  magnetite  in  the  pyroxenes  and  biotite,  but 
the  rod-like  inclusions  are  less  common. 

The  rock  (1427)  100  feet  higher  up  has  the  same  grain  and  structure 
as  the  last,  but  has  less  ferromagnesian  minerals.  The  andesine,  orthoclase, 
and  quartz  are  the  same,  except  that  there  is  a  little  micrographic  inter- 
growth  of  quartz  and  orthoclase.  The  orthoclase  frequently  surrounds 
plagioclase  in  parallel  orientation.  The  ferromagnesian  minerals  are  horn- 
blende, biotite,  magnetite,  and  a  little  pyroxene,  which  is  inclosed  and 
intergrown  in  the  hornblende.  The  latter  is  idiomorphic  and  has  an  olive- 
green  color,  which  is  like  that  of  the  hornblende  in  the  diorite  of  Electric 
Peak.     There   are  numerous  stout  crystals  of  apatite  and   zircon.     One 

'  Brogger,  W.  C,  Die  Eruptivgesteine  des  Kristianiagebietes :  II.  Die  Enipciousfolge  der  tria- 
discheu  Eruptivgesteine  bet  Prodazzo  in  Siidtyrol,  Cbristiania,  1895,  p.  65. 


DIORITE  AND  DIOKlTE-POKPnYKY. '  253 

zircon  inclnsod  in  lu)rnl)k>n(le  is  surrounded  by  a  pleochroic  halo.  The 
chemical  composition  of  this  rock  (analysis  14  on  pa<)e  2()1)  is  that  of  a 
(piartz-mica-diorite  rich  in  orthoclase — that  is,  banatite. 

iri<;her  up  the  spur,  at  10,000  feet,  the  main  body  of  rock  (1429) 
becomes  finer  p-aiued,  the  feldspars  are  more  nearly  idiomorphic,  and  the 
quartz  forms  large,  irregular  individuals  with  raicropoikilitic  structure, 
inclosing  small  felds])ars  (PI.  XXXIII,  fig.  4).  The  plagioclase  is  andes- 
iue,  and  contains  rectangular  inclusions  resembling  glass.  Orthoclase  is 
not  so  abundant.  Tliere  is  considerable  biotite,  with  augite,  hypersthene, 
and  magnetite,  but  no  hornblende. 

A  still  finer-g-rained  form  of  this  quartzose  facies  of  the  core  occurs 
north  of  the  top  of  the  middle  spur.  It  is  a  very  fine-grained  gray  rock 
(1414),  without  phenocrysts.  In  thin  section  it  exhibits  a  structure  similar 
to  that  last  mentioned,  the  idiomorphic  labradorite-andesine  having  a  border 
of  allotriomorphic  feldspar.  There  is  a  moderate  amount  of  augite  and 
hypersthene,  which  occur  in  groups  of  small  grains  rather  than  in  compact 
individuals,  besides  magnetite  and  very  little  biotite.  The  chemical  analysis 
(No.  13  on  page  261)  shows  its  resemblance  to  1427,  as  well  as  the 
chemical  differences  between  them,  which  correspond  to  difference  in  min- 
eral composition,  the  latter  rock  being  richer  in  biotite,  orthoclase,  and 
quartz,  with  more  hornblende  than  pyroxene. 

In  some  of  the  thin  sections  from  the  body  of  the  core  there  are  traces 
of  decomposition,  producing  a  little  chlorite  and  serpentine,  and  in  some 
cases  uralite  accompanying  evidences  of  slight  crushing  in  the  feldspars. 
But  the  rocks  are  to  a  very  great  extent  perfectly  fresh  and  unaltered.  The 
quartzose  facies  of  the  gabbro  is  younger  than  the  main  mass  of  more 
basic  I'ock,  for  it  is  found  cutting  it  as  dikes.  Thus,  a  fine-grained  variety 
(1419),  with  the  same  microsti'ucture  and  composition  as  the  fine-grained 
form  (1414)  on  top  of  the  core,  cuts  the  aphanitic  zone  of  more  pyroxenic 
rock  at  the  base  of  the  middle  spur.  It  grades  directly  into  more  granular 
rock  (1420),  which  has  the  structure  and  composition  of  the  lower  part  of 
the  main  mass  of  the  spur  represented  b}'  1 425. 

There  is  also  a  20-foot  dike  of  this  quartzose  variety  which  cuts  the 
gabbro  on  the  southwest  spur  at  9,100  feet  and  trends  toward  the  southwest, 
while  a  body  of  similar  rock,  whose  form  was  not  observed,  occurs  on  the 
crest  of  the  same  spur,  more  within  the  core.  The  rock  from  this  body 
(1400)  has  the  same  composition  as  that  at  the  base  of  the  middle  spur 


254     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

(1425),  with  more  hornblende  intergrowths.  The  pyroxenes  have  the  char- 
acteristics of  those  in  the  gabbro.  The  microstructure  is  coarser  than  that 
of  the  20-foot  dike,  which  is  represented  by  specimens  1407,  1405,  the 
finer-grained  form  (1405)  being  about  grade  28.  Rock  1400  has  less  ferro- 
magnesian  minerals  and  resembles  in  outward  appearance  the  fine-grained 
rock  from  the  top  of  the  core  (1414).     Its  structure  is  shown  in  PI.  XXXIV, 

Two  small  dikes  of  similar  quartzose  diorite-porphyry  cut  the  aphanitic 
zone  at  the  base  of  the  west  spur.  They  are  dense  and  crystalline,  without 
noticeable  phenocrysts  (1385,  1386).  The  coarser  of  the  two  resembles 
the  rock  last  mentioned  in  mici-ostructure,  and  is  about  grade  27.  It  has 
the  same  mineral  composition  as  the  finer-grained  rock  which  occurs  in  a 
dike  1  foot  wide.  The  latter  (1385)  differs  from  it  slightly  in  microstruc- 
ture, and  is  about  grade  18.  Its  phase  of  crystallization  is  specially  inter- 
esting. In  thin  section  it  consists  of  lath-shaped  feldspars  of  varioiis  sizes, 
and  small  grains  of  feldspar,  with  considerable  quartz,  which  has  a  micro- 
poikilitic  structure.  The  groundmass  also  contains  magnetite,  biotite, 
augite,  and  altered  hypersthene.  Its  most  notable  characteristic  is  the 
development  of  small  phenocrysts  of  orthoclase  in  Carlsbad  twins  with 
irregular  outlines.  The  outer  portion  of  these  crystals  incloses  the  ferro- 
magnesian  minerals,  and  occasionally  plagioclase.  There  are  few  pheno- 
crysts of  plagioclase.  The  orthoclase  appears  to  belong  to  the  period  of 
crystallization  when  the  quartz  formed  in  poikilitic  individuals  of  nearly  the 
same  size  as  the  orthoclase,  but  inclosing  more  plagioclase.  The  outline 
between  the  quartz  and  the  orthoclase  is  irregular.  Thus  the  porphyritical 
orthoclase  crystals  are  younger  than  the  lath-shaped  plagioclase  and  ferro- 
magnesian  minerals  of  the  groundmass  of  the  rock.  The  rocks  are  banatite- 
porphyry. 

There  are  still  more  quartzose  facies  of  the  magma,  which  cut  the 
dioritic  facies  of  the  middle  spur  in  dikes  or  veins.  A  coarsely  crystalline 
variety  (1428)  forms  a  4-foot  dike  cutting  the  main  body  of  rock  (1429), 
which  is  somewhat  finer  grained  and  has  been  described.  The  dike  rock 
is  about  grade  40,  and  is  like  the  main  part  of  the  spur  lower  down  (1425), 
being  of  the  same  degree  of  crystallization.  The  microstructure  is  like 
that  of  the  latter  rock,  but  there  is  more  quartz  and  feldspar  and  less 


DIOIUTE  AND  DIOlUTE-rOKPHYKY.  255 

ferromag'nesian  minerals,  which  are  liiotite  and  a  Httle  chlorite,  but  no 
pyroxene.  Some  of  the  chlorite  carries  zircon  with  i)leochroic  lialos,  and 
bunches  of  rutile  needles.  Magnetite,  zircon,  sphene,  and  stout  apatite 
crystals  are  the  accessory  minerals.  The  rock  is  a  quartz-mica-diorite, 
approaching  granite  in  composition.  It  has  the  same  microstructure,  degree 
of  crystallization,  and  mineral  composition  as  the  quartz-mica-diorite  or 
honiblende-granite  (323)  which  occurs  at  Electric  Peak.  The  latter, 
however,  contains  hornblende  besides  biotite,  and  has  no  chlorite,  which  in 
the  rock  in  Hurricane  Mesa  may  in  part  replace  hornblende.  The  chemical 
composition  of  the  rock  at  Electric  Peak  has  been  determined.  Its  silica 
percentage  is  66.05. 

A  still  more  quartzose  and  feldspathic  variety  (1424)  forms  a  vein  10 
inches  wide  on  the  middle  spur.  It  has  the  general  habit  of  the  rocks  of 
this  facies,  but  is  lighter  coloi'ed  and  carries  less  ferromagnesian  minerals. 
Its  texture  is  saccharoidal.  In  thin  section  it  has  a  granular  structure  about 
grade  40,  and  is  composed  of  quartz,  orthoclase,  and  oligoclase,  with  biotite 
and  magnetite,  very  little  hornblende,  and  some  chlorite.  The  accessory 
minerals  are  the  same  as  in  the  previous  variety.  It  is  a  fine-grained 
granite,  whose  chemical  composition  is  shown  in  analysis  16  on  joage 
261.  Its  microstructure  is  shown  in  PI.  XXXIII,  fig.  3.  There  are  also 
narrow  veins  of  white  rock,  composed  of  quartz  and  feldspar,  with  little  ferro- 
magTiesian  minerals,  and  numerous  small  cavities  lined  with  crystals  of 
quartz  and  feldspar.  These  veins  present  the  most  highly  siliceous  facies  of 
the  rock. 

A  porphyritic  form  of  the  very  quartzose  facies  also  occurs  on  the  mid- 
dle spur.  It  is  not  noticeably  porphyritic  in  the  hand  specimen  (1423),  but 
in  thin  section  is  distinctly  so,  with  a  granular  quartzose  groundmass,  grade 
23.  It  exactly  cori-esponds  in  microstructure  and  degree  of  crystallization, 
as  well  as  in  mineral  composition,  to  the  quartz-mica-diorite-jjorphyry 
(331)  of  Electric  Peak.  The  phenocrysts  are  biotite,  andesine,  and  quartz, 
and  occasionally  orthoclase.  Their  outlines  are  nearly  idiomorphic,  but  the 
quartz  in  some  individuals  loses  its  proper  form  by  merging  into  the  smaller 
quartzes  of  the  gi-oundmass  in  the  manner  described  for  the  rocks  at  Elec- 
tric Peak.  There  is  considerable  sphene  and  zircon.  Its  chemical  compo- 
sition (analysis  15  on  page  261)  is  like  that  of  the  rock  (329)  of  Electric 


256  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Peak,  and  is  quite  the  same  as  that  of  the  quartz-mica-diorite  (1427)  in 
which  it  occurs.  From  its  chemical  composition  it  should  be  classed  with 
banatite. 

Less  quartzose  dioi'ite-porphyries  were  collected  from  talus  at  the  south- 
western base  of  the  southwest  spur,  and  from  that  under  the  cliff  west  of  the 
lake  at  the  head  of  the  west  gulch. 

Having  been  led  from  the  petrographical  study  of  the  breccias  and 
flows  of  glassy  basalt  and  pyroxene-andesite  along  the  converging  lines 
of  microcrystalline  dikes  of  like  composition  to  the  coarsely  granular  core 
of  gabbro  of  the  same  chemical  composition  which  rei:)resents  the  highest 
phases  of  crystallization  of  these  basaltic  magmas,  and  having  found  the 
gabbro  passing  into  more  siliceous  facies  which  have  been  erupted  after  the 
main  mass  of  gabbro,  and  from  which  have  proceeded  dikes  of  finer-grained 
rocks  of  similar  composition,  we  may  follow  these  more  siliceous  dikes  out 
into  the  surrounding  country,  and  consider  in  connection  with  them  the  less 
numerous  dikes  whose  variations  of  mineral  composition  express  a  still  fur- 
ther development  of  facies  of  the  basaltic  magma. 

These  dike  rocks  exhibit  a  wide  range  of  composition,  and,  together 
with  the  dikes  already  described,  form  a  natural  group.  The  latter  repre- 
sent the  main  body  of  magma  in  this  region,  of  which  the  rocks  to  be 
described  may  be  considered  facies  by  differentiation,  the  variations  being, 
on  the  one  hand,  toward  more  siliceous  and  more  feldspathic  rocks,  and,  on 
the  other  hand,  toward  less  siliceous  rocks,  some  of  which  are  highly  feld- 
spathic, while  others  are  high  in  ferromagnesian  minerals.  These  dikes 
appear  to  have  been  erupted  after  the  greater  number  of  basalt  dikes  Avere 
formed,  but  the  exact  relationship  between  them  was  not  observed  in  every 
case. 

Hornbiende-mica-andesite-porphyries. — Commeuciug  witli  tlic  more  siliceous  Varie- 
ties, we  have  a  group  of  light-colored  rocks  in  various  tones  of  gray,  which 
are  compact,  and  are  filled  with  small  plienocrysts  of  feldspar,  hornblende, 
and  biotite.  There  is  a  striking  similarity  of  habit  throughout  the  rocks  of 
the  group,  which  corresponds  to  the  habit  of  the  fine-grained  quartz-mica- 
diorite -porphyries  already  described. 

Within  the  granular  core  they  form  a  few  dikes,  one  of  which  cuts  the 
gabbro  on  the  crest  of  the  southwest  spur,  and  another,  10  feet  wide,  cuts  it 
a  little  higher  and  trends  west.    These  hornblende-mica-andesite-porphyries 


HORNBLENDE  MICA-ANDESITE-rORPHYKIES.  257 

(1401,  1408)  are  not  quite  so  rieh  in  quartz  as  the  diorite-poqihyries  of  the 
core,  l)ut  tlun'  carry  consiih'ralile  tjuartz  in  tlie  ground inass,  and  a  few 
crystals  of  it  occur  as  phenocrysts.  Their  crystallization  is  fii'rade  23  in  the 
first  case,  and  grade  IH  in  the  second. 

Near  the  base  of  the  west  spur  there  is  an  S-foot  dike  of  this  rock 
(1 384),  trending  west  of  south,  and  still-  lower  down  the  slope  there  is  another 
(1381).  A  small  dike  of  this  rock  cuts  the  soutliAvestern  edge  of  the  top 
i>f  the  middle  spur,  and  in  the  cliff  west  of  the  lake  thei'e  is  a  15-foot  dike  of 
it  (1367),  trending  N.  45°  W.  Besides  these  there  are  indications  of  other 
bodies  of  the  same  kind,  fragments  of  which  are  found  in  the  talus  in 
various  places.  These  rocks  are  fine  grained,  and  resemble  the  remainder 
of  the  dikes  of  hornblende-mica-andesite-porphyry  so  closely  that  a  general 
description  will  serve  for  all  of  them. 

The  outlying  dikes  of  this  character  are  found  in  the  immediate  neigh- 
borhood of  the  core,  the  longest  noted  extending  about  5  miles  to  the  south- 
west. A  10 -foot  dike  of  it  forms  the  saddle  northwest  of  the  plateau  of 
Hurricane  Mesa  and  trends  northwest,  being-  in  line  with  the  15-foot  dike 
west  of  the  lake. 

On  the  narrow  ridge  south  of  Closed  Creek  there  are  a  nuinber  of 
these  dikes,  which  cut  the  ridge  at  a  ^jlnce  southwest  of  the  core.  Five 
were  noted,  three  of  which  are  10,  18,  and  20  feet  wide  and  trend  toward 
the  south  and  southwest.  They  fork  and  branch  out  in  these  directions, 
and  dikes  of  identical  rock  are  exposed  on  the  southern  slope  of  the  ridge, 
having  the  same  general  trends.  They  may  be  traced  almost  continuously, 
in  some  instances  diagonally,  across  the  steep  spurs. 

In  thin  section  the  rocks  are  holocrystalline  and  fine  grained,  ranging 
from  grade  18  in  the  dike  (1381)  at  the  base  of  the  southwest  spur  of  the  core 
to  grade  10  in  the  most  remote  dike  (1319),  which  is  4  or  5  feet  wide.  The 
habit  of  the  rocks  is  andesitic,  passing  into  that  of  andesite-porphyry  at  the 
more  crystalline  end  of  the  series.  The  groundmass  consists  of  tabular 
plagioclase  in  a  matrix  of  irregular  grains  of  feldspar  with  a  little  quartz, 
besides  idiomorphic  crystals  of  magnetite,  biotite,  hornblende,  and  pyroxene. 
Through  this  are  scattered  larger  crystals  of  the  same  minerals.  The  mega- 
scopic crystals  are  abundant,  and  are  andesiue-labradorite  .with  zonal  struc- 
ture and  variable  amounts  of  inclusions;  and  idiomorphic  hornblende,  brown- 
ish green  with  a  brown  Ijorder,  in  places  intergi'own  with  augite  in  the 

MON  XXXII,  PT  II 17 


258  GEOLOGY  OF  THE   YELLOWSTONE  NATIONAL  PARK. 

same  manner  as  in  the  rocks  of  Electric  Peak.  Augite  is  pale  gi'een,  and 
occurs  in  small  amounts.  Hypersthene  is  often  decomposed.  Biotite  is 
abundant  in  the  groundmass  of  some  of  the  rocks  when  it  does  not  form 
large  cr^-stals.  In  other  cases  it  is  abundant  as  phenocrysts.  Some  of 
the  more  altered  rocks  carry  chlorite  and  epidote.  Apatite  and  zu'con 
appear  as  accessory  minerals.  When  the  biotite  has  been  altered  to  chlorite 
the  zircon  inclusions  are  sometimes  surrounded  by  pleochroic  halos. 

There  are  more  siliceous  and  feldspathic  varieties  of  the  rock,  in  which 
biotite  preponderates  over  hornblende.  The  groundmass  carries  less  ferro- 
magnesian  minerals,  and  a  distinctly  micropoikilitic  structure  is  recognized 
in  the  quartz. 

From  the  foregoing  it  is  evident  that  we  have  followed  this  fades  of 
the  magma  from  the  core  out  int(i  microcrystalline  forms,  which  may  be 
classed  as  andesitic  forms  of  hornblende-mica-andesite-porphyry,  or  as 
holocrystalline  andesites.  The  chemical  analysis  of  the  most  distant  dike 
of  this  rock  (1319)  (analysis  12  on  page  261)  shows  that  it  belongs  to  a 
less  siliceous  phase  of  the  general  magma  than  the  quartz-mica-diorite  of  the 
core.  No  highly  siliceous  dikes  were  found  outside  of  the  core  in  connection 
with  this  system  of  intrusions.  Similar  rocks  occur  in  the  neighborhood 
of  Cook  City  in  such  a  ma;mier  as  to  indicate  the  presence  of  another  center 
of  eruption  near  that  place. 

The  more  basic  dikes  which  remain  to  be  described,  though  they  are 
scattered  over  the  district  and  are  somewhat  sporadic,  may  properly  be 
considered  to  belong  to  the  Crandall  center,  since  varieties  of  them  occur 
within  the  core,  although  the  extreme  forms  do  not.  They  are  less  numerous 
than  those  just  described,  and  vary  considerably  in  mineral  composition. 

Hornbiende-pyroxene-andesite. — There  are  ouly  two  of  thcsc  dlkcs  wliicli  may 
be  classed  as  hornblende-pyroxene-andesite,  but  dikes  of  this  rock  are  more 
numerous  in  the  neighborhood  of  Cook  City.  One  of  these  rocks  (1317) 
forms  a  dike  on  the  ridge  northeast  of  Indian  Peak  and  trends  toward  the 
gabbro  core.  The  other  (1368)  was  found  on  the  top  of  Hurricane  Mesa 
east  of  the  core,  but  not  in  place.  It  carries  large  black  crystals  of  horn- 
blende from  10  to  20  mm.  long.  Both  of  the  rocks  mentioned  are  compact, 
with  hornblende,  as  the  only  prominent  phenocrysts.  In  thin  section  the 
groundmass  is  andesitic  and  holocrystalline,  and  consists  of  lath-shaped 
plagioclase  microlites  with  tluidal  arrangement,  besides    small  patches  of 


MINERAL  AND  CHEMICAL  VAKIATIONS  OF  KOCKS.  259 

quartz  with  iiiayiietite  aiul  altered  pynixeiie.  Tlio  plieuocrysts  vary  in 
aiiu»uut  and  size,  and  are  plagioclase,  auyite,  and  lijperstliene,  witli  larger 
crj'stals  of  hornblende,  which  is  brown  and  brownish  green  and  in  one  of 
the  rocks  has  a  narrow  border  of  magnetite. 

Lamprophyric  rocks. — The  remaining  dikes  do  not  constitute  a  distinct  group 
which  may  be  sharply  separated  fntm  the  majority  of  the  rocks  of  the  dis- 
trict, though  certain  of  them  possess  marked  characteristics.  Their  chiet 
distinction,  is  an  unusual  mineral  combination,  but  they  are  connected  with 
the  ordinary  rocks  of  the  district  by  mineralogically  interniediate  varie- 
ties. In  general  appearance  they  resemble  the  rocks  with  which  they  are 
associated. 

They  are  fine-grained  rocks,  characterized  by  an  abundance  of  biotite 
and  other  ferromagnesian  minerals,  including  augite  and  olivine,  with  feld- 
spar subordinate  in  some  cases,  and  partly  alkaline,  while  analcite  appears 
as  a  secondary  mineral  in  some  modifications  of  the  rock.  In  other  cases 
the  rocks  are  distinctly  feldspathic.  Because  of  their  unusual  composition, 
and  of  the  occun-ence  of  similar  rocks  in  dikes  and  lava  flows  in  other  parts 
of  the  Yellowstone  Park,  their  petrographical  description  is  deferred  to  Chap- 
ter IX,  where  they  are  classed  as  absarokites,  shoshonites,  and  banakites,  and 
are  considered  as  exceptional  facies  of  the  normal  magma  of  the  region. 
They  seem  to  represent  less  common  differentiations  of  this  magma  than 
the  more  numerous  varieties  of  igneous  rocks  do,  and  for  this  reason  may 
be  discussed  separately. 

MINERAL  AND  CHEMICAL  VARIATIONS  OF  THE  ROCKS. 

The  variations  in  minei'al  composition  of  the  igneous  rocks  of  this  dis- 
trict are  evidently  dependent  on  more  than  the  chemical  composition  of  the 
magmas  from  which  they  have  crystallized,  rocks  of  the  same  or  of  similar 
chemical  composition  ha^'ing  diff'erent  mineral  components,  which  has  also 
been  shown  to  be  the  case  at  Electric  Peak  and  Sepulclu'e  Mountain. 

The  range  of  mineral  variation  among  the  extrusive  rocks,  when  con- 
sidered in  the  order  of  their  eruption,  is  from  siliceous  andesites  with  biotite 
and  hoi-nblende,  through  those  with  hornblende  and  pyroxene,  to  pyroxene- 
andesites,  which  grade  into  basalt  by  decreasing  percentages  of  hypersthene 
and  increasing  amounts  of  olivine. 

This  is  succeeded  in  a  neighboring  part  of  the  country  by  a  recuiTence 
of  the  same  series  from  hornblende-mica-andesite  to  basalt,  and  finally  by 


260 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 


rhyolite  and  basalt.  There  are  three  distinct  periods  of  basaltic  eruptions 
and  an  indefinite  number  of  minor  outbursts  of  the  same  rock.  The  study 
of  the  whole  region  shows  the  frequent  recurrence  of  certain  lavas. 

Among  the  intrnsive  rocks  the  mineralogical  variations  differ  according 
to  the  phase  of  crystallization  of  the  rock.  In  the  finer-grained  dike  I'ocks 
they  range  from  olivine-augite-labradorite-basalts,  through  those  with  little 
or  no  olivine,  to  hornblende-pyroxene-andesites  and  to  still  more  siliceous 
mica-hornblende-pyroxene-andesite-porphyries,  and  in  another  direction  to 
more  basic  rocks,  which  range  from  olivine-augite-mica  rocks,  through 
augite-mica  rocks,  to  augite-hornblende-mica  rocks  with  orthoclase  and 
plagioclase. 

There  is  also  a  mineral  variation  which  accompanies  the  degree  or 
phase  of  crystallization  of  the  rock.  It  is  illustrated  by  the  transition  from 
basalt  to  gabbro.  The  character  of  the  variation  will  be  shown  by  a  com- 
parison of  the  mineral  composition  of  rocks  whose  chemical  composition  has 
been  determined  to  be  similar. 


An 

alynes  0 

f  rochs 

from  th 

e  Cranilall  volt 

ano. 

Constituent. 

1 

2 

3 

i 

5 

6 

7 

8 

SiO, 

51.81 

.77 

52.09 
.39 

52.11 

.53 

53.56 
.68 

53.71 
.74 

53.89 
.49 

55.93 

.81 

56.21 

.88 

TiOa 

AI5O3 

15.24 

17.84 

16.58 

16.07 

18.00 

18.81 

18.32 

18.24 

Fe^O:, 

3.66 

4.27 

3.66 

3.21 

3.99 

4.92 

2.39 

3.26 

FeO 

4.86 

4.36 

4.99 

5.29 

4.05 

2.81 

4.91 

3.69 

MuO 

.08 

.14 

.23 

.11 

.24 

.17 

.14 

.17 

MgO 

8.89 

5.33 

6.87 

7.23 

5.19 

3.29 

3.97 

3.38 

CaO  

9.06 

8.03 

6.43 

8.77 

6.88 

5.42 

6.17 

5.91 

NajO 

2.83 

3.39 

3.25 

3.06 

3.50 

3.65 

4.29 

4.15 

KiO 

2.08 

1.98 

3.20 

1.94 

3  10 

2.98 

2.62 

3.02 

p„05 

.18 

.27 

.63 

.18 

.38 

.52 

.56 

.64 

NiO 

CI 

1 

1 

H:0 

Total 

.67 

1.77 

1.99 

.19 

.55 

2.99 

.22 

.78 

100. 13 

100.06 

100. 47 

100. 29 

100.33 

99.94 

100.33 

100.  33 

1.  Gabbro-porphyry ;  core  ou  Hurricane  Mesa,  CrandaU  Basin  (1388). 

2.  Basalt;  flow,  north  side  of  Timber  Creek.  C'raudall  Basiu  (1252). 

3.  Basalt;  dike,  ridge  south  of  Hurricane  Mesa,  CrandaU  Basin  (1325). 

4.  Basalt-porphyry;  core.  Hurricane  Mesa,  CrandaU  Basin  (1383). 

5.  Gabbro  (with  raica) ;  core,  Hurricane  Mesa,  CrandaU  Basiu  (1430). 

6.  Basalt-andesite  glass,  breccia;  ridge  south  of  Indian  Peak,  CrandaU  Basin  (1241). 

7.  Orthoclase-gabbro-dioriti;  (rich  in  raica) ;  core,  Hurricane  Mesa,  Crandal]  Basin  (1399). 

8.  Orthoclase-gabbro-diorite  (rich  in  mica);  core,  Hurricane  Mesa,  CrandaU  Basiu  (1396). 


OHliMlCAL  ANALYaKS  OF  KOOKS. 
Analyses  of  rockn  from  the  Crandall  volcano — Continued. 


261 


CoDStltuent. 

9 

10 

11 

12 

61.  16 

.23 

16.17 

2.89 

2.18 

Truce. 

3.89 

4.26 

3.87 

3.20 

.13 

13 

63.42 

.35 

17.16 

3.09 

1.50 

.04 

1. 64 

4.65 

4.  .51 

3.04 

.26 

.19 

14 

15 

16 

SiO.                                

57.26 

.76 

19.40 

2.49 

3.29 

.16 

2.57 

5.68 

4.21 

2.95 

.51 

57.32 

.62 

17.29 

3.89 

3.03 

.06 

3.50 

5.81 

3.89 

3.04 

.50 

.10 

57.64 

.77 

18.43 

3.63 

2.84 

.10 

3.32 

5.49 

4.03 

3.33 

.34 

63.97 

.4X 

15.78 

2.  35 

1.87 

.05 
2.84 
8.71 
4.36 
4.01 

.40 
Trace. 

64.40 

.40 

15.77 

2.47 

1.15 

.04 

2.12 

3.54 

4.10 

3.  HI 

.16 

.17 

71.62 

TiO. 

.08   ; 

14.99    , 

1.27    j 

1.01 

.17 

.74 

1.33 

3.62 

4.81 

Trace. 

AliOj 

Fe  Oj 

KeO                   

MnO       

MgO 

CaO  

Na.O 

K.O 

p  .0, 

NiO   

CI 

Trace. 
.51 

HO  

.86 

.63 

2.09 

.44 

.58 

2.  24 

.41 

- 

Total 

100. 14 

99.74 

100. 43 

100.07 

100.  29 

100.40 

100.  37 

100. 05 

9.  Dioritic  facies  of  gabbro;  core,  Hurricane  Mesa,  Crandall  Basin  (1436). 

10.  Monzonite;  east  core.  Hurricane  Mesa,  Crandall  Basin  (1442). 

11.  Pyroxene-diorite-porphyry.  approaching  iiiouzonite-porpliyry;  intrusive  sheet,  Hurricane  Mes.i, 

Crandall  Basin  (1372). 

12.  Honibleudemioa-andesite-porpbyry ;     dike,    ridge   south   of    Hurricane    Mesa,    Crandall    B.TSin 

(1319). 

13.  Quartzdiorite  (tine  grained) ;  core.  Hurricane  Mesa,  Crandall  Basin  (1414). 

14.  Quartz-mica-diorite;  core.  Hurricane  Mesa,  Crandall  Basin  (1427). 

15.  Quartz-niica-diorite-porphyry ;  core.  Hurricane  Mesa.  Crandall  Basin  (1423). 

16.  Aplite;  dike  in  core.  Hurricane  Mesa,  Crandall  Basin  (1424). 

The  chemical  analyses  show  what  is  known  of  the  composition  of 
the  sm'face  flows,  dikes,  and  stock  rocks  of  this  district,  exclusive  of  those 
classed  as  absarokites,  etc.  Of  these  analyses,  Nos.  1,  2,  3,  4,  5,  6,  7,  8, 
9,  11,  12,  and  16  were  made  by  Mr.  L.  G.  Eakins,  and  Nos.  10,  13,  14, 
and  15  by  the  late  Dr.  W.  H.  Melville,  in  the  chemical  laboratory  of  the 
United  States  Geological  Survey.  They  are  arranged  according  to  the 
increasing  percentage  of  silica,  which  varies  from  51.81  to  71.62.  The 
range  of  silica  is  greater  than  in  the  rocks  of  Electric  Peak  and  Sepulchre 
Mountain,  most  of  the  analyses  showing  less  than  58  per  cent  silica.  The 
more  siliceous  rocks  in  both  localities  are  similar.  The  variability  of 
the  chemical  composition  of  the  rocks  of  this  district  has  been  discussed 
in  another  place.^  The  analyses  shoAv  that  the  basalts  of  the  district  vary 
in  composition  within  certain  limits. 

'Iddings,  J.  p.,  The  origin  of  igneous  rocks:  Bull.  Philos.  Soc.  Washington,  Vol.  XII,  1892,  p.  151. 


262  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Comparin^'^  the  first  three  analyses  (1,  2,  3),  it  is  seen  how  closely  they 
agree  with  one  another.  The  first  has  slightly  less  alumina  and  somewhat 
more  magnesia  and  lime.  The  second  and  third  are  of  basalts,  the  second 
being  a  surface  flow,  and  the  third  a  dike.  They  are  rich  in  olivine,  augite, 
and  magnetite,  without  hypersthene.  The  third  contains  large  pheno- 
crysts  of  labradorite,  and  can'ies  a  little  orthoclase  in  the  groundtnass. 
The  first  of  the  three  analyses  is  of  the  finest-grained  form  of  one  of  the 
series  of  specimens  from  the  core,  and  is  a  gabbro-porphyry.  Its  compo- 
nent minerals  are  plagioclase  with  much  augite,  hyperstliene,  biotite,  and 
magnetite,  and  a  little  olivine.  Although  it  is  richer  in  magnesia  and  has 
only  two-thirds  as  much  potash  as  the  third  rock,  it  has  developed  a  great 
amount  of  biotite,  much  hypersthene,  and  onl}-  a  little  olivine,  while  the 
third  rock  has  abundant  olivine  and  no  biotite  or  hypersthene. 

Comparing  the  next  three  analyses  (4,  5,  6),  we  find  a  close  corre- 
spondence in  chemical  composition,  with  a  smaller  amount  of  alumina  and 
alkalies  in  the  first  and  a  greater  amount  of  iron,  lime,  and  magnesia.  The 
fifth  analysis  holds  an  intermediate  place  between  the  fourth  and  sixth. 
The  greatest  variation  is  in  the  magnesia,  which  is  twice  as  great  in  the 
fourth  as  in  the  sixth.  The  rocks  represent  three  very  different  phases  of 
consolidation.  The  sixth  (1241)  is  a  glass  with  few  crystals  of  olivine, 
augite,  and  plagioclase,  and  microlites  of  magnetite,  augite,  and  feldspar. 
The  fourth  is  a  fine-grained  basalt-porphyry,  composed  of  plagioclase, 
augite,  hypersthene,  biotite,  and  magnetite,  with  no  olivine.  The  fifth  is 
coarsely  granular  gabbro,  composed  of  plagioclase  with  some  orthoclase,  a 
little  quartz,  much  augite  (diallage),  some  hypersthene,  considerable  biotite 
and  magnetite,  and  a  few  crystals  of  olivine. 

The  next  two  analyses  (7,  8)  are  only  a  little  higher  in  silica  than  the 
previous  three,  and  are  very  similar  to  that  of  the  basalt-andesite  glass 
(1241)  in  all  other  respects.  They  are  analyses  of  coarsely  crystalline 
gabbro-diorite,  which  grades  into  less  siliceous  rock  (1388)  within  a  short 
distance.  There  are  no  analyses  of  extrusive  rocks  from  this  district 
with  the  same  percentage  of  silica  with  which  to  compare  them,  but  at 
Sepulchre  Mountain  there  are  andesites  whose  chemical  composition  has 
been  determined,  and  with  which  these  may  be  compared. 


CHEMICAL  ANALYSES  OF  ANDliSITES. 


263 


Analygcx  of  andesUen  from  Seiinlclirf  Mountain. 


CoilMf  itiU-llt. 

4'JI 

171 

407 

388 

SiO- 

55.83 
1.05 

17.11 

4.07 

3.75 

Niine. 

7.40 

55.92 

.94 

17.70 

3.16 

4.48 

Trace. 

5.90 

56.61 

.79 

13.62 

r..  89 

2.  60 
.35 

6.61 
.14 

5.48 
Trace. 

57.17 
1.03 

17.25 

2.48 

4.  .31 

None. 

6.61 

TiO. 

AU> 

Fe.-O:, 

FcO 

MuO 

CaO 

BaO 

Mg( » 

5.05 

4.34 

4.83 

.SrO 

LiO 

Nunc. 

2.  94 

1.71 

.21 

Trace. 

None. 

.09 

4.08 

2.28 

.18 

Trace. 

None. 

Trace. 

3.44 

2.03 

.05 

Trace. 

Trace. 

Na,0 

K,0 

3.13 

2.71 

.06 

P,Or, 

SO:, 

CI 

CO. 

None. 
2.27 

HO 

1.28 

1.42 

1.20 

LessO  forC'l 

100.  40 

100. 45 

100.26 

100.40 

These  analyses  are  liig-her  in  magnesia  and  lime  and  a  little  lower  in 
alumina  and  alkalies.  The  rocks  from  wliich  they  were  made  are  pyroxene- 
andesite  and  hornblende-pyroxene-andesite,  without  mica  or  olivine.  Their 
coarsely  crystalline  equivalents  at  Electric  Peak  are  pyroxene-andesite- 
porphyry  and  pyroxene-mica-diorite.  The  rocks  from  which  analyses 
7  and  8  were  made  are  orthoclase-gabbro-diorite.  They  consist  of  plagio- 
clase  with  some  orthoclase  and  a  little  quartz,  much  biotite,  augite,  hyper- 
sthene,  and  magnetite,  and  a  little  hornblende,  but  no  olivine.  When 
compared  with  the  corresponding  granular  rocks  at  Electric  Peak,  they  are 
found  to  differ  from  them  in  having  less  hornblende  and  more  augite  and 
hypersthene,  with  less  quartz  and  considerable  orthoclase. 

The  next  three  analyses  in  the  table  (9,  10,  11)  are  .shghtly  more 
siliceous,  and  are  all  from  intrusive  bodies.  They  are  similar  to  the  pre- 
vious analyses,  but  the  ninth  shows  more  alumina  and  less  magnesia.  This 
rock  is  very  coarse  grained  and  feldspathic,  and  is  a  diorite  facies  of  the 
gabbro.  The  tenth  is  the  fine-grained  monzonite  with  the  poikilitic  ortho- 
clase and  little  biotite,  besides  much  augite,  hypersthene,  and  magnetite,  and 


264     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

very  little,  if  any,  quartz.  The  eleventh  is  a  pyroxene-diorite-porphyry 
approaching  monzonite-porphyry,  which  is  very  fine  grained  and  is  com- 
posed of  plagioclase,  augite,  h}-persthene,  magnetite,  and  some  biotite  and 
a  little  quartz,  Avith  no  olivine,  but  paramorphs  after  olivine,  now  consisting 
of  augite,  l^iotite,  and  magnetite.  It  also  contains  microscopic  feldspars, 
which  are  in  part  orthoclase. 

The  twelfth  analysis  is  still  higher  in  silica,  with  somewhat  lower 
alumina,  lower  lime,  and  about  the  same  alkalies.  The  rock  is  a  dike  of 
hornblende-mica-andesite-porphyry  with  phenocrysts  of  andesine-labra- 
dorite,  hornblende,  and  biotite,  besides  a  small  amount  of  augite  and 
hypersthene.  The  groundmass  is  microcrystalline,  and  consists  of  feldspar 
and  the  ferromagnesian  minerals  just  named,  with  considerable  magnetite. 
There  is  a  little  chlorite  or  ser[)entine.  It  is  interesting  to  compare  this 
rock  with  that  of  the  Indian  Creek  laccolith. 

The  next  three  analyses  (13,  14,  15)  are  of  diorites  that  form  part 
of  the  core  of  the  volcano.  They  have  nearly  the  same  percentage  of 
silica,  but  that  with  lowest  silica  has  highest  alumina  and  lime  and  low- 
est magnesia  and  potash.  This  rock  also  differs  from  the  others  miner- 
alogically.  It  is  a  very  fine-grained  rock  without  phenocrysts.  It  consists 
of  labradorite-andesine  and  a  small  amount  of  orthoclase  and  quartz, 
besides  a  moderate  amount  of  augite,  hyjjersthene,  and  magnetite,  and 
very  little  biotite.  The  second  of  the  three,  with  G3.97  per  cent  of  silica, 
is  of  a  coarser-grained  quartz-mica-diorite,  composed  of  andesine  with  a 
nearly  equal  amount  of  orthoclase  and  quartz,  besides  considerable  biotite 
and  hornblende,  some  magnetite,  and  a  little  pyroxene.  The  third  of  these 
three  analyses  is  of  a  quartz-mica-diorite-porphyry,  with  abundant  quartz. 
The  phenocrysts  are  biotite,  andesine,  and  quartz,  and  occasionally  ortho- 
clase. 

It  corresponds  chemically  to  the  diorite  last  described,  and  is  almost 
exactly  the  same  mineralogically  and  structurally  as  one  of  the  quartz- 
mica-diorite-porphyries  (331)  of  Electric  Peak,  and  chemically  it  resembles 
another  of  those  rocks  (329). 

The  sixteenth  analysis  is  of  a  fine-grained  granite  which  forms  a 
10-inch  vein  in  the  diorite.  It  consists  of  quartz,  orthoclase,  and  oligo- 
clase,  with  biotite  and  magnetite,  besides  a  very  little  hornblende  and  some 
chlorite. 


CHYSTALLIZATION.  265 

From  till'  t'orcji'dinji-  it  is  evident  that  magmas  which  may  crystallize 
into  extrusive  mcks  whose  essential  minerals  are  plagioclase,  augite,  and 
olivine  may  crystallize  into  coarsely  granular  rocks  with  plagioclase, 
augite,  Inpersthene,  and  biotite,  with  a  small  amount  of  orthoclase  and 
quartz,  with  or  without  hornblende;  and  that  olivine  may  be  present  in 
some  cases,  when  the  other  magnesian  nu'nerals  will  be  less  abundant. 

Hornblende,  which  is  so  important  a  constituent  of  the  diorite  of 
Electric  Peak,  jdays  a  very  subordinate  role  in  the  granular  rocks  of  Hurri- 
cane Mesa.  Biotite  becomes  more  pronounced  as  the  rocks  become  more 
granuhu'.  Hypersthene  also  develops  under  the  same  conditions.  And 
orthoclase  and  quartz  make  their  apjjearance  in  the  granular  equivalents  of 
many  basalts.  Thus  we  find  minerals  that  are  chai'acteristic  of  more  and 
more  siliceous  members  of  the  series  of  extrusive  rocks  developed  in  basic 
magmas  under  conditions  which  render  the  magmas  more  highly  crystalline 
and  more  or  less  granuhir. 

These  minerals,  then,  are  in  part  functions  of  the  chemical  composition 
of  igneous  magmas,  while  in  part  they  are  functions  of  the  phase  of  crystal- 
lization of  chemically  identical  or  similar  magmas.  This  is  another  demon- 
stration of  the  law  that  "the  molecules  in  a  chemically  homogeneous  fluid 
magma  combine  in  various  ways  and  form  quite  different  associations  of 
silicate  minerals,  producing  mineralogically  different  rocks." 

CRYSTALLIZATION. 

It  may  be  well  to  call  attention  to  some  of  the  conditions  under  which 
the  molten  magmas  within  the  dikes  and  the  core  of  the  Crandall  volcano 
must  have  solidified.  Referring  to  the  profile  sections  of  the  district  and 
the  probable  outline  of  the  ancient  volcano  (PI.  XXXII),  it  is  evident  that 
the  magmas  which  cooled  within  that  portion  of  the  core  which  is  now 
exposed,  and  those  in  the  dikes  within  a  radius  of  2  miles,  must  have  occu- 
pied positions  at  nearly  the  same  distance  beneath  the  surface  of  the  volcano. 
And  if  the  former  may  be  considered  to  have  solidified  10,000  feet  below 
this  surface,  then  the  latter  must  have  solidified  10,000  feet  below  the  surface. 
The  one  is  as  deep  seated  as  the  other,  and  yet  their  degrees  of  crystallization 
range  from  glassy  to  coarsely  granular.  The  influence  of  jjressure  alone  on 
the  crystallization  of  these  rocks  is  not  recognizable  in  the  size  of  the  grain 
or  in  the  phase  of  crystallization. 


266     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

The  changes  of  crystallization  may  be  traced  horizontally  in  the  imme- 
diate vicinity  of  the  core,  increasing  from  the  outlying  bodies  toward  the 
core,  the  change  being  rapid  near  the  core  and  accompanied  by  induration 
and  metamorphism  of  the  surrounding  rocks.  It  is  in  great  measure  inde- 
pendent of  the  size  of  the  body,  since  nari'ow  dikes  within  the  core  are 
coarsely  crystalline,  while  much  broader  ones  in  the  surrounding  country 
are  very  fine  grained. 

It  was  unquestionably  the  diiferences  in  the  temperature  of  the  core 
rocks  and  of  the  outlying-  breccias  which  determined  the  degree  of  crystal- 
lization. The  core  was  undoubtedly  much  more  highly  heated  than  the 
surrounding  rocks,  and  the  bodies  of  magma  that  solidified  within  it  cooled 
much  more  slowly  than  those  injected  into  the  outlying  parts  of  the  vol- 
cano, or  even  within  a  mile  of  the  central  conduit. 

From  this  it  follows  that  the  application  of  the  terms  "deep-seated" 
and  "  abyssal "  to  coarsely  crystalline  rocks  is  misleading,  since  it  is  not 
distinctive  and  applies  equally  well  to  rocks  of  totally  different  crystalline 
characters.  The  depth  at  which  a  magma  has  solidified  appears  to  be  of 
little  moment  in  comparison  with  the  temperature  of  the  rocks  surrounding  it. 

DEVELOPMENT  OF  PHENOCRYSTS. 

A  consideration  of  the  various  mineralogical  phases  of  rocks  which 
have  the  same  chemical  composition,  as  they  occur  in  this  district,  leads  to 
important  conclusions  regarding  the  crystallization  of  phenocrysts.  The 
great  majority  of  the  basaltic  dikes  carry  porphyritical  crystals  of  olivine, 
augite,  and  plagioclase  in  a  microcrystalline  groundmass  of  plagioclase, 
augite,  and  magnetite.  In  other  varieties  the  phenocrysts  are  almost 
wholly  olivine  and  augite.  Within  the  core  there  are  rocks  with  pheno- 
crysts of  augite  and  plagioclase,  sometimes  with  olivine,  sometimes  with 
paramorphs  after  olivine.  The  outlines  of  these  crystals  show  that  their 
crystallization  continued  uninterruptedly  into  the  period  of  crystallization 
of  the  groundmass.  These  rocks  are  more  generally  the  fine-grained 
forms.  The  greater  part  of  the  gabbro  does  not  carry  olivine,  or  at  least 
oidy  in  occasional  crystals,  while  the  augites  possess  characters  different 
from  those  in  the  basalt;  besides  which,  hypersthene  and  biotite  have 
developed  in  crystals  as  large  as  those  of  augite.  It  is  also  observed  that 
the  apatite  and  magnetite  ai-e  differently  developed,  being  in  larger  and 
fewer  individuals  in  the  coarse-grained  rocks. 


DEVELOPMENT  OF  PHEXOCRYSTIS.  2H7 

From  this  it  is  evident  that  inrt«i:inas  of  similar  cliomical  comjiositinii, 
which  were  erupted  at  diti'ereut  times,  reached  positions  of  Hke  elevation 
within  the  volcano  in  different  stages  of  crystallization.  8ome  can-ied 
large  crystals  of  plagioclase,  augite,  and  olivine,  some  only  aiigite  and 
olivine,  and  others  had  no  crystals  developed  in  them.  For,  as  shown  in 
the  chapter  on  Electric  Peak  (Chapter  III),  the  molten  magmas  must  have 
been  completely  fluid  when  they  reached  those  places  in  the  conduit  where 
the  character  of  crystallization  referable  to  the  surrounding  conditions 
affected  all  of  the  constituent  minerals,  including  the  apatite  and  zircon. 

From  the  fact  that  the  magma  which  was  forced  into  the  outlying 
dikes  nuist  have  been  the  advanced  portion  of  that  which  stopped  in  the 
conduit  in  any  particular  eruption,  and  since  the  dike  rocks  are  more 
usually  porphyritic,  and  the  core  or  stock  rocks  show  by  their  micro- 
structure  and  mineral  development  that  they  Avere  generally  completely 
fluid  when  they  came  to  rest  in  the  conduit,  it  may  be  inferred  that  the 
phenocrysts  of  the  dike  rocks  were  formed  in  the  advanced  portion  of  the 
magma  of  a  particular  eruption,  and  that  the  rear  part  of  the  magma  was 
in  most  cases  free  from  them. 

The  magma  having  been  assumed  to  be  chemically  homogeneous,  and 
the  influence  of  pressure  not  being  recognized  in  the  crystallization  of 
these  rocks,  the  most  variable  condition  which  remains  is  the  temperature  of 
the  rocks  through  which  the  magma  flowed,  and  the  consequent  difference 
in  the  rate  of  cooling  of  the  advanced  portion  of  the  magma  and  of  the  rear 
portion.  The  former  would  cool  more  rapidly.  While  the  magma  advances 
through  hot  rocks  it  may  cool  gradually,  but  when  it  enters  less  highly 
heated  rocks  the  cooling  will  be  more  rapid. 

There  are  many  reasons  for  concluding  that  the  phenocrysts  of  porphy- 
ritic rocks  are  the  result  of  crystallization  which  has  taken  place  very  shortly 
before  the  final  solidification  or  crystallization  of  the  whole  rock  mass,  and 
that  they  are  comparatively  rapid  growths,  and  are  not  minerals  that  have 
existed  within  the  molten  magma  for  any  considerable  length  of  time  prior 
to  its  solidification. 

As  indicating  their  rapid  growth,  we  may  cite  the  abundant  inclusions 
of  mother  liquor  with  gas  cavities,  which  are  of  common  occurrence  in 
phenocrysts  in  extrusive  rocks;  and  that  they  could  not  have  existed  for 
any  great  length  of  time  within    the  molten  magma   is   proved  by  the 


268     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

uniform  distribution  instead  of  the  segregation  of  the  heavier  minerals 
in  feldspathie  magmas,  such  as  j^henoerysts  of  augite  and  magnetite  in 
rhyohte.  Tlie  specific  gravity  of  the  former,  about  3.3  and  6,  is  so  much 
greater  than  that  of  even  the  sohdified  magma  in  the  form  of  obsidian,  2.3, 
that  it  is  difficuh  to  imagine  how  fairly  large  crystals  of  these  minerals  could 
have  remained  suspended  for  any  length  of  time  in  this  matrix  when  it  was 
in  a  fluid  state. 

Cross '  has  called  attention  to  certain  large  crystals  of  orthoclase  in 
dacite-porphyries  ("quartz-porphyrites  ")  and  in  granular  diorites  in  Colo- 
rado, which  appear  to  have  crystallized  after  the  magmas  of  tliese  rocks  had 
been  erupted  and  had  come  to  rest.  And  Pirsson  has  presented,  in  a  paper 
read  before  the  eleventh  annual  meeting  of  the  Greological  Society  of 
America,  further  evidence  of  the  relatively  late  growth  of  phenocrysts  in 
many  por^jhyritic  rocks. 

'  Cross,  W.,  The  laccolitic  mountain  grouiisoi  Colorado,  Utah,  ami  Arizona  :  Fourteenth  Ann. 
Kept.  U.  S.  Gcol.  Survey,  1895,  p.  229. 


CHAPTER    VIII. 

THE  IGNEOUS  KOCKS  OF  THE  AH8AR0KA  RANGE  AND 
TWO  OCEAN  PLATEAU  AND  OF  OUTLYING  PORTIONS 
OF   THE    YELLOWSTONE   NATIONAL   PARK. 


By  JosETH  Paxson  Iddings. 


INTRODUCTION. 

The  volcanic  lavas  that  were  erupted  from  the  chain  of  ancient  vol- 
canoes situated  along  the  eastern  border  of  the  Yellowstone  Park,  and  from 
minor  vents  lying  outside  of  this  range,  were  to  a  very  great  extent  tuffs 
and  fragrnental  material.  They  were  thrown  over  large  areas  of  country, 
and  often  traveled  long  distances,  so  that  after  erosion  had  reduced  the 
size  of  these  vast  accumulations  of  tuff- breccia,  not  only  wei'e  the  original 
forms  of  the  bodies  destroyed,  but  deposits  that  may  have  been  at  one  time 
connected  have  become  separate.  Thus,  it  is  not  always  possible  to  decide 
whether  isolated  areas  of  volcanic  breccia  belong  to  neighboring  larger 
bodies  or  are  the  result  of  local  eruptions. 

In  the  present  chapter  no  attempt  will  be  made  to  describe  the  mode 
of  formation  or  the  history  of  the  lavas  of  these  portions  of  the  Park,  or 
the  topographic  features  of  the  Absaroka  Mountains.  Descriptions  of 
these  will  be  found  in  chapters  by  Mr.  Arnold  Hague  in  Part  I.  I'he 
petrographic  treatment  of  the  rocks  in  this  chapter  will  be  confined  to  an 
account  of  their  field  occurrence  and  distribution  and  to  a  systematic 
description  of  their  mineralogical  characteristics  and  composition.  The 
account  of  their  occurrence  and  distribution  must  of  necessity  proceed 
along  geographical  lines,  which  may  be  followed  either  upon  the  map  of 
the  Yellowstone  Park  accompanying  this  monograjjh  or  on  the  atlas  sheets 
of  folio  30  of  the  Geologic  Atlas  of  the  United  States,  issued  by  the  Geo- 
logical Survey.     For  convenience,  we  shall  start  at  the  northern  boundary 

269 


270  GEOLOGY  OF  THE  YELLOWSTOJS^E  ^^ATIOJSTAL  PAEK. 

of  the  Park,  and  mentiou  the  lavas  forming  the  mountains  east  of  the 
Yellowstone  River,  from  the  northern  boundary  southward.  Those  in  the 
vicinity  of  Soda  Butte  Creek  and  east  of  Lamar  River  have  been  described 
in  connection  with  the  dissected  volcano  of  Crandall  Basin,  but  their  men- 
tion again  here  will  serve  to  make  clear  the  connection  of  that  volcano 
with  others  that  combined  to  form  the  Absaroka  Range.  In  proceeding 
from  the  north  southward,  the  rocks  encountered  will  follow  one  another 
more  nearly  according  to  the  order  of  their  eruption,  the  youngest  being 
found  farthest  south. 

EARXrY  ACID  BRECCIA. 

The  volcanic  ejectamenta  of  the  Absaroka  Range  rest  upon  crystalline 
schists  and  sedimentary  rocks  in  the  vicinity  of  the  northern  border  of  the 
Yellowstone  Park.  The  contact  is  exposed  along  the  valley  of  Clark  Fork, 
Soda  Butte  Creek,  Slough  Creek,  and  lower  Lamar  and  Yellowstone  rivers. 
In  all  of  these  localities  there  are  exposures  of  light-colored  andesitic 
breccia,  often  variegated  in  color.  These  represent  masses  of  various 
dimensions,  sometimes  very  large.  They  rest  immediately  upon  the  schists 
and  sedimentary  rocks,  and  are  overlain  by  dark-colored  breccia.  In  some 
places  the  two  grade  into  each  other  gradually;  in  others  there  is  a  well- 
defined  plane  of  contact,  and  evidences  of  a  period  of  erosion,  between  the 
deposition  of  the  two  breccias.  The  gradation  between  the  two  indicates 
continuous  deposition,  or  that  both  belong  to  a  prolonged  series  of  erup- 
tions, during  which  the  composition  of  the  lavas  changed.  A  precisely 
similar  relation  between  lower  acid  and  upper  basic  breccias  obtains  at 
Sepulchre  Mountain,  where  the  volcanic  activity  was  synchronous  with 
that  of  the  volcanoes  of  the  Absaroka  Range. 

Exposures  of  the  early  acid  breccia  are  few,  and  their  areas  are  com- 
paratively small,  in  the  region  about  to  be  described  In  the  vicinity  of  Junc- 
tion Butte,  immediately  over  the  gneiss  there  is  tuff-breccia  of  light-colored 
acid  andesite  and  trachytic  rhyolite,  quite  the  same  as  those  west  of  Yellow- 
stone River  in  the  neighborhood  of  Crescent  Hill,  and  undoubtedly  part  of 
the  same  formation.  These  breccia  deposits  have  been  more  or  less  worked 
over  by  water  and  rearranged,  and  include  many  fragments  of  gneiss  and 
schist.  Similar  lavas  and  Ijreccia  with  buff-colored  tuff  (1025,  1026,  1032) 
and  some  massive  hornblende-andesite  (1024)  form  the  top  of  the  north- 
western end  of  Specimen  Ridge.     The  trachj'te  is  brecciated  with  lumps  of 


EARLY  ACID  lUtKOOlA,  ABSAKOKA  KANGE.  2'('l 

turt'  and  iilteivd  pcrlite  liavinfr  distinct,  perlitic  stnictnre  (1027,  102«,  1031, 
10i{2).  Trarlivtt'  also  tornis  the  base  ot"  Junction  Uutte,  and  rests  upon 
the  ••neiss  directh'  noith.  It  also  forms  the  banks  of"  the  river  at  the 
mouth  of  Slou"h  Creek.  The  acid  andesitic  breccia  extends  several  miles 
farther  up  the  Lamar  Kivcr  and  is  o\erlain  by  a  lava  sheet  of  j)orphyritic 
basalt  (112!l).  The  ])reccia  is  dense  and  dark  colored  and  might  be 
mistaken  for  l)asic  breccia,  but  contains  nuich  biotite  and  even  minute 
phenocrvsts  of  (juartz.  The  acid  breccia  is  cut  by  a  3-foot  dike  of  pyroxene- 
andesite,  which  is  dark  colored  and  has  small  phenocrysts  of  pyroxene  and 
feldspar  (1038),  The  relative  age  of  these  rocks  is  thus  plainly  shown  in 
this  locality. 

Mica-bearing  andesitic  breccia  occurs  at  the  northern  base  of  Speci- 
men Ridge,  about  a  mile  west  of  Crystal  Creek.  It  is  green,  com])act,  and 
carries  dark-colored  frag-ments.  It  may  be  a  mixture  with  more  basic 
andesites.  The  onh-  other  exposures  of  the  earliest  acid  .breccia  in  this 
viciuit)'  are  in  Cache  Creek  and  near  Cook  City.  These  have  been 
described  in  connection  with  the  Crandall  volcano.  The  acid  breccias  in 
all  of  these  localities  are  the  same.  But  in  some  cases  thei'e  is  more  or  less 
of  an  admixture  of  basic  material.  Of  course  there  are  localities  where 
the  basic  breccia  rests  directl}'  upon  the  nonvolcanic  rocks.  Either  the 
first  acid  breccia  was  not  so  extensive  as  the  basic  breccia  or  it  was  com- 
pletely removed  by  erosion  in  some  places. 

The  microscropical  study  of  specimens  collected  from  bodies  of  the 
earliest  acid  breccia  shows  it  to  var}*  in  mineral  composition,  the  varieties 
falling  under  three  classes :  Hornblende-mica-andesite,  hornblende-andesite, 
and  hornblende-pyroxene-andesite.  The  fragments  constituting  any  large 
mass  often  differ  considerably  among  themselves  iu  habit,  color,  and  min- 
eral composition.  Sometimes  their  characters  are  nearly  constant  for  large 
bodies  of  breccia.  Massive  bodies  occur  either  as  lava  streams  or  as  intru- 
sive masses.  In  most  places  mica-bearing  varieties  abound.  They  are 
seldom  absent.  But  the  relative  proportions  of  the  different  varieties  is  not 
constant  enough  to  permit  a  close  estimate  to  be  made  of  the  average  com- 
position of  the  whole.  The  following  analyses  represent  the  chemical 
composition  of  the  three  varieties,  one  of  which  has  been  already  given  in 
connection  with  the  description  of  the  Electric  volcano. 


272 


GEOLOGY  OF  THE  YELLOWSTONE  I^'ATIONAL  PARK. 

Analyses  of  rocks  occur  rim/  in  early  acid  breccia,  Absaroka  Range. 


Constituent. 

1 

2      ' 

3 

SiOi 

61.56  ; 

.87 

14.73 

4.47 

1.23 

.34 
3.57 
4.87 

64.61 

Noue. 

18.62 

2.78 

.95 

Trace. 

.85 

4.20 

67.95 

.45 

14.98 

2.33 

.95 

.09 

1.42 

3.98 

.23 

4.39 

2.86 

TiO 

A1>0,.--     -                        

YeiO:, 

FeO 

MnO 

MgO 

CaO 

BaO  

Na.O 

.5.10 
2.24 

4  37 

2.36 

.01 

.30 

KO 

LiO 

PO, 

.04 

.07 
.11 
.37 
.61 

SO 

Loss  lit  105° 

H,0 



1.42 

.93 

100.44     : 

1 

99. 88 

100.  79 

The  first  is  a  massive  rock  iu  the  early  acid  breccia  near  the  head  of 
Tower  Creek.  The  second  is  from  the  breccia  of  Crescent  Hill,  and  is 
above  the  average  in  percentage  of  silica,  jvidging  from  the  mineral  com- 
position of  the  breccia  as  a  whole.  The  third  is  from  early  acid  breccia  of 
Sepulchre  Mountain,  and  is  considerably  above  the  average  for  silica.  It 
is  probable  that  the  average  percentage  of  silica  for  the  whole  of  these 
earlv  acid  breccias  is  62  or  63. 

These  rocks  are  usually  lig-ht  gray,  with  greenish,  reddish,  and  purplish 
tones,  sometimes  having  darker  colors.  The  appearance  of  the  breccia  is 
g-enerally  variegated.  It  may  be  loosely  aggregated,  but  is  oftener  com^iact 
and  indurated.  The  habit  of  the  andesite  fragments  varies  from  those  with 
aljundant  small  phenocrysts  of  feldspar,  biotite,  hornblende,  and  pyroxene 
to  those  with  fewer  and  larger  phenocrysts  of  the  same  minerals,  which 
seldom  exceed  5  mm. 

The  groundmass  is  glassy  in  some  cases,  usuall}'  colorless  glass  filled 
with  rectangular  and  prismatic  crystals  of  feldspar  and  fewer  microscopic 
crystals  of  the  other  constituent  minerals,  including  pyroxene  in  many  cases. 
C)r  the  groundmass  may  be  microlitic  with  little  or  no  glass,  or  holocrystal- 


EARLY  AUID  BRECCIA,  ABSAROKA  RANGE.  273 

line  ofi'i^'liiij?  into  niicropoikilitic  structures,  wliicli  indicate  that  the  rock  frag- 
ments are  broken  portions  of  voU-anic  cones  where  the  hivas  had  crystal- 
lized us  dikes  and  other  intrusive  bodies.  The  shape  of  the  fragments, 
usuallv  angular,  is  such  as  to  show  that  most  of  the  breccia  was  formed  by 
the  explosion  of  ah-eady  solidified  lavas,  which  had  consolidated  near  the 
centers  of  volcanic  action.     Few,  if  any,  exhil)it  the  slaggy  surface  of  bombs. 

The  phenocrvsts  are  sharply  idiomorphic,  and  zonal  structure  is  well 
developed  in  the  felds[)ars,  wliich  often  contain  numerous  glass  inclusions. 
The  feldsjiars  are  almost  wholly  polysynthetic  twins,  in  the  lime-soda 
feldspar  series,  their  optical  properties  indicating  oligoclase  and  oligoclase- 
andesine.  Sanidine  is  seldom  present;  in  fjict,  is  almost  entirely  absent. 
It  is  found  in  some  associated  tufts,  but  may  have  been  derived  from  the 
trachytic  lava  occun-ing  in  the  vicinity  of  Junction  Valley.  The  feldspars 
are  sometimes  quite  free  froni  inclusions;  in  other  cases  they  contain  minute 
crystals  of  the  other  constituent  minerals,  as  well  as  portions-  of  the 
gToundmass. 

Biotite  forms  six-sided  plates,  often  rather  thick.  Its  color  is  brown  to 
red,  with  marked  absorption  parallel  to  the  plane  of  cleavage,  and  some- 
times with  strong  pleochroism  between  orang-e,  red,  and  light  yellow. 
Grreenish  yellows  also  occur.  Frequently  the  hornblende  exhibits  the  same 
colors  as  the  biotite  in  the  same  rock,  both  being  red,  or  both  brown  or 
greenish  brown.  Apparently  tlie  same  cause  affected  the  color  of  both 
minerals  at  the  same  lime.  Often  the  biotite  is  brown  when  the  hornblende 
is  greenish  brown,  or  even  green.  Biotite  resists  decomposition  longer 
than  hornblende  in  many  cases.  It  is  often  free  from  inclusions,  but  fre- 
quently contains  magnetite,  apatite,  or  zircon,  and  less  often  the  other 
mineral  constituents.  In  some  cases  it  has  a  border  of  magnetite  grains, 
or  may  be  more  or  less  completely  changed  to  a  pseudomorph  of  magnetite 
with  or  without  pyroxene.  This  is  usually  accompanied  by  like  changes  in 
the  hornblende. 

Hornblende  has  its  customary  stoiit  prismatic  forms,  usually  with  colors 
like  those  of  biotite,  but  green  tones  occur  more  frequently  than  in  biotite. 
The  pleochroism  is  that  ordinarily  observed.  Often  free  from  inclusions,  it 
sometimes  abounds  in  them,  glass  and  magnetite  being  the  common  kinds. 
Paramorphism  to  magnetite  and  augite  occurs,  as  with  biotite.  Intergrowths 
with  pyroxene  are  occasionally  seen.     Pyroxenes  are  more  numerous  in 

-18 


274  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

those  rocks  in  which  biotite  is  scarce,  but  both  also  occur  together,  accom- 
panying' hornblende.  The  pyroxenes  are  nionoclinic  and  orthorhombic 
species.  Malacolite  or  augite  is  pale  green  in  thin  section,  with  no  ple- 
ochroism.  Hypersthene  is  more  or  less  pleochroic  with  pale  colors  in  thin 
section;  green  parallel  to  the  prismatic  axis,  and  reddish  perpendicular  to 
it.  The  optical  characters  are  the  same  as  those  of  these  minerals  in  the 
pyroxene-andesites,  and  they  will  be  more  particularly  described  under 
that  heading. 

Quartz  phenocrysts  are  occasionally  seen  in  the  more  siliceous  rocks 
approaching  dacite  in  composition.  Microscopic  quartz  is  abundant  in  the 
groundmass  of  the  more  crystalline  varieties. 

Magnetite  is  always  present  in  microscopic  crj'stals,  and  a^jjjears  to  be 
the  form  of  iron  oxide  common  to  this  group  of  andesites.  Titanium  oxide 
is  present  in  only  small  amounts.  It  is  to  be  remarked  in  this  connection 
that  titaniferous  iron  oxide  occurs  in  the  rhyolites  of  this  region,  where  it 
shows  itself  in  the  cb.aracter  of  the  alteration  product,  which  appears  to  be 
leucoxene.  Apatite,  in  short  stout  crystals,  is  usually  colorless,  but  is 
sometimes  gray,  yellowish,  or  red.  The  latter  colors  occur  when  the  bio- 
tites  and  hornblendes  are  more  or  less  reddened.  Zircon  is  always  present 
in  small  amounts  and  in  minute  crystals. 

The  subdivision  of  rocks  into  hornblende-mica-andesites,  hornblende- 
andesites,  and  hornblende-pyroxene-andesites  is  based  on  the  relative  pro- 
portions of  the  ferromagnesian  minerals.  All  three — biotite,  hornblende, 
pyroxene — may  be  present  together,  those  in  very  small  amounts  being 
left  out  of  the  name  of  the  rock.  In  general,  the  first  group  is  the  most 
siliceous,  the  second  next,  and  the  third  least  of  the  three.  But  the  tran- 
sition through  the  mineralogical  series  is  not  strictly  coordinate  with  the 
transition  in  the  chemical  series,  so  far  as  the  silica  is  concerned.  More- 
over, we  know  that  the  mineral  composition  of  a  rock  is  not  rigidly  con- 
cordant with  the  chemical  composition.  So  that  rocks  that  might  be  classed 
as  hornblende-andesite  and  others  that  are  hornl^lende-pyroxene-andesite 
may  be  alike  chemically. 

As  already  said,  some  fragments  of  the  overlying  breccia  are  mingled 
in  places  with  the  acid  breccia;  hence  the  collections  from  these  masses  in 
some  cases  contain  basic  andesites,  such  as  pyroxene-andesite. 


EARLY  BASIC  liRKCCIA  AND  FLOWS.  275 

EARLY  BASIC  BRECCIA  AND  ASSOCIATED  BASALTIC  FLOWS. 

This  breccia  includes  all  of  the  darker-colored  breccia,  with  some  light- 
colored  breccia,  which  directly  overlies  the  early  acid  breccia  and  which 
consists  mainly  of  pyroxene-andesites,  with  some  hornblende-pyroxene- 
andesites  and  basaltic  andesites  and  l)asalts. 

By  correlation  it  corresponds  to  the  basic  breccia  of  Sepulchre  Moun- 
tain and  that  west  and  south  of  the  Gallatin  Mountains.  It  constitutes  the 
great  accumulation  of  basic  breccia  that  formed  the  bulk  of  the  volcano  of 
Crandall  Basin,  including  the  mountain  masses  from  Index  Peak,  through 
those  on  both  sides  of  Soda  Butte  Creek  to  Sloug-h  Creek,  south  through 
Fossil  Forest  and  Slirror  Plateau,  to  the  mountains  surrounding  the  drain- 
age of  Lamar  River  and  the  drainage  of  Crandall  Creek.  Basic  breccia 
connected  with  this  extends  along  the  mountain  range  east  of  the  head  of 
the  Stinkingwater  River  and  west  up  to  the  tributary  canyons,  and  under- 
lies the  summits  of  the  northern  half  of  the  Absaroka  Range  within  the 
boundary  of  the  Yellowstone  Park. 

Basic  breccia  forms  the  mountains  north  of  Lamar  River,  including 
Bison  and  Druid  peaks  and  the  high  ridges  on  both  sides  of  Pebble  Creek 
and  Soda  Butte  Creek,  the  bedding  in  all  of  these  masses  being  nearly 
horizontal,  with  a  slight  dip  toward  the  south.  They  appear  to  be  continu- 
ous with  the  breccia  south  of  Lamar  River,  and,  as  akeady  pointed  out  in 
Chapter  VII,  they  may  be  considered  as  the  outlying  base  of  the  Crandall 
A'olcano.  In  these  breccias  pyroxene-andesite  is  the  prevalent  rock,  horn- 
blendic  varieties  being  less  common,  and  basaltic  varieties  subordinate. 

Associated  with  these  breccias — that  is,  intercalated  in  them  at  the  base — 
are  several  sheets  of  basaltic  rock,  which  are  exposed  in  disconnected 
bodies  along  the  bottom  of  the  valley  of  Lamar  River  and  Soda  Butte 
Creek.  They  distinctly  underlie  the  great  mass  of  the  basic  breccia  where 
they  are  exposed  on  Soda  Butte  Creek  and  near  its  junction  with  Lamar 
River.  They  also  overlie  some  of  the  same  kind  of  breccia.  The  charac- 
teristics of  these  basaltic  rocks  are  sufficiently  pronounced  to  distinguish 
them  from  a  much  more  recent  basalt,  whose  eruption  was  posterior  to  the 
excavation  of  the  present  valley  of  Lamar  River,  and  which  will  be 
described  later  on.  The  older  basaltic  rock  is  found  over  the  acid  breccia 
and  trachytic  breccia  in  the  vicinity  of  Junction  Butte  and  about  the  mouth 


276  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  Slough  Creek.  A  remnant  caps  the  breccia  on  the  east  side  of  Yellow- 
stone Canyon,  opposite  the  hot  springs  above  Baronett  Bridge  (1126).  It 
is  dark,  dense,  and  crystalline,  with  a  slightly  resinous  luster.  It  has  large 
tabular  phenocrysts  of  plagioclase,  some  8  or  10  mm.  long,  but  none  of  augite 
or  olivine.  Another  sheet  of  basalt  at  the  north  base  of  Specimen  Ridge 
is  dark  and  dense,  with  many  medium-sized  phenocrysts  of  tabular  plagio- 
clase, and  fewer  of  augite  (1127).  A  somewhat  similar  basalt  overlies  the 
acid  breccia  just  east  of  the  mouth  of  Crystal  Creek.  It  is  dense  and  full 
of  medium  and  large  phenocrysts  of  feldspar  and  augite.  It  is  partly 
amygdaloidal  with  agate  and  quartz  (1128).  Over  it  is  another  sheet  of 
dense  basalt,  dark  and  crystalline,  with  many  large  phenocrysts  cf  rec- 
tangular and  tabular  feldspars,  and  fewer  and  less  noticeable  augites  (1130). 

A  similar  basaltic  rock  occurs  farther  east,  at  the  south  base  of  Bison 
Peak.  It  is  dense,  has  a  slightly  resinous  luster,  and  is  filled  with  large 
brilliant  feldspars  and  numerous  smaller  augites,  and  contains  some  amj^g- 
dules  of  zeolite  (1131).  Similar  basalt  occurs  at  the  southwestern  base  of 
Druid  Peak  (1132).  It  is  underlain  by  a  massive  sheet,  which  is  dense  and 
crystalline,  with  abundant  large  phenocrysts  of  tabular  plagioclase  10  mm. 
long,  and  fewer  and  smaller  augites  (1133).  Farther  east,  at  the  first  gulch 
below  the  mouth  of  Soda  Butte  Creek,  basalt  similar  to  the  last  is  exposed 
200  feet  above  the  river  (1135).  Three  miles  up  Soda  Butte  Valley  a  basalt 
cliff  exposes  a  sheet  of  dense  black  rock,  with  abundant  small  phenocrysts 
of  feldspar  and  augite  (1137). 

These  rocks  have  a  peculiar  mineral  composition  that  distinguishes 
them  from  ordinary  basalts.  They  are  like  some  of  the  basaltic  lavas 
occun-ing  in  the  upper  parts  of  this  breccia,  or  overlying  it,  which  are  char- 
acterized b}^  a  varying  content  of  orthoclase,  and  since  they  have  never 
been  described  in  detail  their  specific  characters  will  be  given  in  Chapter 
IX,  which  is  devoted  to  a  general  description  of  all  similar  rocks  occurring 
within  the  Yellowstone  Park. 

The  basic  breccias  belonging  to  the  main  mass  of  the  Crandall  volcano, 
and  forming  the  mountains  on  Cache  and  Calfee  creeks  and  the  body  of 
Saddle  Mountain,  extend  across  Lamar  River  toward  the  west  and  south 
and  constitute  the  basal  portion  of  Mirror  Plateau  and  of  the  mountains 
between  Lamar  River  and  the  head  of  Stinkingwater  River. 

Overlying  this  breccia  in  Mirror  Plateau  are  numerous  sheets  of  basalt, 


EARLY  BASIC  BKEOOIA  AND  FLOWS.  277 

with  some  intercalated  layers  of  scoria  and  breccia,  forming  a  compound 
sheet  700  to  1,000  feet  thick.  This  massive  sheet  caps  the  northeastern 
spurs  of  Mirror  I'lateau  and  forms  the  eastern  half  of  its  top,  passing  west- 
ward under  rhyolite.  The  basalts  of  this  sheet  differ  somewhat  in  outward 
appearance.  Some  are  dark  and  dense,  with  small  phenocrysts.  Others 
have  a  semi  waxy  luster  and  belong  to  the  orthoclase-bearing  varieties 
already  mentioned. 

West  of  the  mouth  of  Cold  Creek  irregularly  bedded  basic  breccia 
forms  the  lower  thousand  feet  of  the  ridge  between  this  creek  and  Willow 
Creek.  Immediately  over  it  is  a  sheet  of  porphyritic  basalt,  with  pheno- 
crysts of  felds})ar  and  jDyroxene.  This  sheet  is  200  feet  thick,  and  consti- 
tutes the  base  of  the  broad  shoulder  which  sets  back  from  the  steep  face  of 
the  ridge. 

East  of  the  mouth  of  Cold  Creek  basic  breccia  fomns  the  lower  1,500 
feet  of  the  northern  end  of  the  flat-topped  mountain  east  of  Pyramid  Peak, 
and  rises  still  higher  in  the  next  peak  east,  which  is  just  beyond  the  one 
hundi-ed  and  tenth  meridian.  Here,  at  9,850  feet  elevation,  it  forms  the 
northern  summit  of  the  peak,  the  breccia  being  rough  and  ulibedded  and 
dark  gray  in  color  (1472).  The  northern  face  of  the  peak  is  precipitous, 
and  consists  of  rudely  bedded  breccia  can-3'ing  masses  3  feet  in  diameter. 
The  rock  bears  abundant  phenocrysts  of  pyroxene  and  feldspar,  and  is 
mostly  dark  colored,  in  places  red.  On  the  southern  slope  of  this  ^^eak  it 
is  composed  of  very  small  fragments  (1473)  in  a  jnn-plish-red  matrix. 

Horizontal  basalt  flows  cap  the  next  peak  south,  whose  summit  is 
about  10,025  feet  in  altitude,  and  also  form  the  top  of  the  ridge  to  the  east 
and  the  smooth  table-topped  mountain  lying  southeast.  The  basalt  on  the 
peak  is  dense,  with  few  phenocrysts  of  olivine  (1475,  1476).  It  proves  to 
be  a  leucite-bearing  shoshonite,  described  in  Chapter  IX.  Other  flows  of 
basalt  in  this  neighborhood  are  more  porphyritic. 

The  precipitous  exposures  on  the  ridge  east,  and  on  the  south  face  of 
the  twin  peaks  Castor  and  Pollux,  show  the  lower  .parts  of  these  mountain 
masses  to  be  made  of  similar  dark,  rough,  and  rudely  bedded  or  unbedded 
breccia.  But  the  upper  thousand  feet,  above  the  10,000-foot  line,  consists 
of  nearly  horizontal  sheets  of  basalt  of  various  thicknesses.  The  slope  of 
the  top  of  the  table  mountain  south  is  at  a  slight  inclination  westward. 

The  basalt  sheets  extend  westward  across  the  saddle  at  the  southeastern 


278  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

end  of  the  flat-topped  mountain  east  of  Pyramid  Peak,  and  form  the  upper 
600  feet  of  this  mountain,  the  bottom  of  the  sheets  lying'  at  about  9,000 
feet  altitude,  and  resting  on  basaltic  breccia.  The  character  of  the  different 
sheets  varies  somewhat,  a  highly  vesicular  and  strongly  porphyritic  basalt 
(1477)  being  found  at  the  northern  end. 

Glaciation  has  left  its  marks  upon  the  surface  of  these  table-lands, 
having  planed  out  lake  basins  and  deposited  rounded  drift.  The  extension 
of  the  basalt  sheets  westward  is  clearly  indicated  by  the  topography  of 
Pyramid  Peak.  From  the  saddle  northward  there  is  a  flat  bench  or  series 
of  benches  along  the  eastern  base  of  the  pyramidal  peak,  which  Ijroaden  out 
into  a  flat-topped  spur  between  the  branches  of  Cold  Creek.  The  basalt 
passes  beneath  the  upper  thousand  feet  of  this  mountain  and  descends  steeply 
into  the  valley  of  Cold  Creek,  thence  across  a  broad  spur  into  Mist  Creek, 
north  of  which  it  forms  the  basalt  ledges  already  noticed,  which  are  con- 
tinuous with  those  of  Mirror  Plateau. 

The  same  or  similar  basic  breccia,  topped  by  sheets  of  massive  basalt, 
continues  southward  along  the  base  of  the  mountain  forming  the  west  wall 
of  Stinkingwater  Canyon,  and  extends  far  up  the  valleys  draining  the 
region  lying  east  of  the  watershed  of  the  Yellowstone  Lake.  As  in  the 
vicinity  of  Lamar  River,  these  breccias  and  lava  flows  I'epresent  the  ancient 
slopes  of  basaltic  volcanoes  lying  east  of  the  one  hundi'ed  and  tenth 
meridian.  Along  Jones  Creek,  Crow  Creek,  and  Middle  Creek  basaltic 
breccia  forms  the  lower  portion  of  the  eastern  end  of  the  mountain  ridges. 
It  is  overlain  by  successive  sheets  of  porphyritic  basalt,  which,  on  the 
northern  side  of  Middle  Creek,  attain  a  total  thickness  of  between  900  and 
1,000  feet.  In  each  of  these  three  valleys  the  basalt  ledges  have  given 
rise  to  high-shouldered  spurs  and  benches  on  either  side  of  the  valleys,  in 
the  same  manner  as  on  Cold  Creek.  The  surface  of  the  basalt  flows 
descends  gradually  to  the  westward,  and  disappears  beneath  more  recent 
breccia  in  the  heads  of  the  valleys.  The  character  of  the  basalt  is  similar  to 
that  near  Lamar  River.  Some  of  the  flows  are  full  of  large  phenocrysts  of 
feldspar  and  pyroxene  (1530);  others  exhibit  only  large  olivines  (1527). 

This  early  basic  breccia,  with  its  associated  basaltic  lavas  of  peculiar 
composition,  continues  beyond  the  divide  at  the  head  of  Middle  Creek, 
through  Sylvan  Pass,  and  forms  the  mountains  and  ridge  as  far  as  the  shore 
of  Yellowstone  Lake  at  Signal  Point.     It  also  occurs  in  isolated  patches  at 


EARLY  BASIC  BRECCIA  AND  FLOWS.  279 

the  head  of  the  southwestern  brancli  of  ^MicUHe  Creek,  and  on  the  other 
side  of  the  divi(U'  at  the  head  of  Hocky  Creek,  beneath  more  recent  Hght- 
coh>red  acid  brt^ccia. 

On  the  southern  side  of  Sylvan  Pass  breccia  of  pyroxene-andesite  is 
highly  indui'ated  by  the  many  dikes  that  traverse  it,  and  the  pyroxenes  are 
more  or  less  iiralitized.  At  the  forks  of  Middle  Creek,  east  of  this,  it  is 
full  of  larjji'e  ])hent)crysts  of  pyroxene  and  resembles  much  of  the  basalt  of 
the  Crandall  Basin,  and  at  Si<>nal  Point  and  near  Park  Point,  on.  Yellow- 
stone Lake,  there  are  basalts  and  breccia  of  this  type  (1616-1619).  Signal 
Ridge  and  the  mass  of  Grizzly  Peak  are  composed  of  pyroxenic  breccia 
without  prominent  phenocrysts,  with  some  olivine  and  little  or  no  horn- 
blende, while  hornblende  ajipears  in  the  breccia  at  the  summit  of  Grizzly 
Peak  (1521-1625). 

An  isolated  exposure  of  basaltic  rocks  belonging  to  this  series  occurs  at 
the  head  of  the  southeastern  branch  of  Beaverdam  Creek  and  just  north  of 
Coulter  Creek.  At  this  place  there  are  two  horizontal  sheets  of  porphyritic 
basalt,  one  upon  the  other,  and  over  them  is  a  light-colored  tuff  of  trachytic 
rock,  with  many  inclosed  fragments  of  basalt  and  andesite.  This  tuff  cor- 
responds to  the  trachytic  tuff  in  the  neighborhood  of  Junction  Butte. 

Almost  precisely  similar  basaltic  lavas  and  trachytic  tuff  occur  at  Two 
Ocean  Pass,  beneath  the  basic  andesitic  breccia  which  forms  Two  Ocean 
Plateau,  and  though  the  exact  period  of  eruption  of  these  basaltic  lavas,  as 
compared  with  the  basalts  of  the  Crandall  volcano,  is  a  matter  of  uncertainty, 
still  on  purely  petrographical  grounds  they  may  be  described  in  this  con- 
nection. 

On  the  northern  side  of  Two  Ocean  Pass  there  is  a  ledge  of  basaltic 
rocks  conaposed  of  five  sheets  resting  directly  one  on  another.  The  basalt 
of  the  different  sheets  varies  somewhat  and  belongs  to  the  group  of  sho- 
shonites.  That  of  the  top  one  is  a  dark,  dense  rock,  with  rather  small 
phenocrysts  of  feldspar,  augite,  and  decomposed  olivine  (1715).  The  top 
surface  is  red,  the  middle  of  the  flow  dense,  and  the  bottom  somewhat 
vesicular.  The  top  has  probably  been  eroded.  The  sheet  below  is  similar, 
with  numerous  large  feldspars  and  altered  olivines  (1716).  ■  It  is  vesicular 
in  the  upper  portion,  dense  in  the  middle,  and  slightly  vesicular  at  the  bot- 
tom, and  is  25  feet  thick.  Beneath  this  is  a  layer  of  scoria  2  or  3  feet  thick, 
having  the  character  of  the  imderlying  flow,  which  is  full  of  large  feldspars, 


280  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

is  dense  in  the  middle,  but  vesicular  for  2  or  3  feet  at  the  bottom  (1717). 
It  is  about  20  feet  thick  and  is  filled  with  zeolites  (1722)  and  calcite,  which 
line  cavities  and  cracks. 

This  sheet  rests  directly  on  the  slaggy,  scoriaceous  top  of  the  next 
lower  one,  which  is  a  basalt  with  only  a  few  phenocrysts  of  pyroxene 
(1718).  It  is  distinctly  vesicular  for  some  depth  (1719).  The  lowest  sheet 
is  a  dark,  dense  basalt  with  numerous  phenocrysts  of  augite  and  olivine 
(1720).  The  top  and  bottom  of  the  sheet  are  vesicular  (1721).  This 
basalt  extends  across  the  valley  south.  It  rests  on  assorted  basic  breccia, 
and  may  be  traced  west  along  the  northern  side  of  the  valley  for  2  miles 
(1724),  where  it  is  similar  to  the  upper  two  sheets  at  Two  Ocean  Pass. 
The  more  crystalline  forms  of  these  basalts  have  a  slightly  resinous  luster. 

The  petrographical  character  of  the  rocks  constituting  the  early  basic 
breccia  is  variable  within  limits,  and  is  slightly  different  in  the  two  princi- 
pal localities  mentioned,  Sepulchre  Mountain  and  Crandall  volcano.  In  all 
cases  it  is  pyroxeue-andesite  in  large  part,  grading  into  hornblende- 
pyroxene-andesite  on  the  one  hand  and  into  olivine-bearing  andesite  and 
basalt  on  the  other.  At  Sepulchre  Mountain  the  hornblendic  end  of  the 
series  is  more  pronounced  and  the  basaltic  end  is  subordinate.  But  it  is 
to  be  remembered  that  the  size  of  the  mass  of  this  mountain  is  insignificant 
when  compared  with  that  of  the  groups  of  mountains  embraced  in  the 
Crandall  volcano.  The  breccias  more  directly  connected  with  the  Crandall 
volcano  are  largely  pyroxene-audesites,  only  a  very  small  jJi'opoi'tion  of 
which  carry  hornblende.  Basaltic  forms  are  very  abundant,  and  true 
basalts  preponderate  in  the  upper  parts  of  the  volcano.  The  bulk  of  this 
breccia  lies  within  the  district  already  described  as  the  dissected  volcano  of 
Crandall  Basin,  and  its  petrographical  characters  have  been  given  in 
Chapter  VII. 

The  basaltic  lava  flows  or  streams  connected  with  this  breccia,  as 
already  pointed  out,  occur  partly  near  its  base,  as  do  the  flows  ex2)osed  in 
the  lower  Lamar  River  Valley  and  in  the  valley  of  Soda  Butte  Creek.  The 
greater  part  constitutes  the  thick  accumulation  of  lava  sheets  forming  Mirror 
Plateau  and  the  summits  of  the  mountains  immediately  south  of  Lamar 
River.  The  petrographical  character  of  these  rocks  is  somewhat  variable. 
A  large  number  of  sheets  consist  of  normal  andesitic  basalt — that  is,  basalts 
with  abundant  phenocrysts  of  lime-soda  feldspar  (labradorite-bytownite), 


ACID  BRECCIA  OF  PYRAMID  PEAK.  281 

aufjite,  ami  olivine,  and  occasionally  hyperstliene,  in  different  proportions 
in  different  cases.  In  some  rocks  the  phenocrysts  are  large;  in  others,  small. 
Augite  is  usually  tlie  most  prominent  mineral.  The  groundmass  is  glassy 
and  microlitic,  or  holocrystalline,  with  lime-soda  feldspar,  augite,  and  mag- 
netite, and  having  the  various  modiiications  of  microstructure  characteristic 
of  basic  andesitic  lavas.  Olivine,  which  is  abundant,  is  in  some  cases  partly 
decomposed  to  green  serpentine,  in  others  to  orange  or  red  serpentine,  which 
apjK'ars  to  pass  into  the  mica-like  mineral  having  similar  colors  and  indices 
of  refraction,  but  marked  pleochroism,  with  strong  absorption  for  rays 
vibrating  parallel  to  the  plane  of  perfect  cleavage.  The  perfect  cleavage 
appears  to  be  parallel  to  some  plane  in  the  prismatic  zone  of  olivine. 

Other  bodies  of  these  rocks  have  an  exceptional  composition,  and  for 
this  reason  will  be  described  in  detail  in  Chapter  IX,  together  with  other 
similar  rocks  in  the  region. 

XiATE  ACID  BRECCIA. 

Overlying  the  massive  basalts  that  top  the  early  basic  breccia,  and  in 
marked  contrast  to  their  dark-gray  or  black  color,  are  breccias  and  tuffs  of 
light-colored  and  brightly  variegated  andesites.  This  superposition  is 
clearly  shown  in  Pyramid  Peak  and  on  the  flat-topped  mountain  east  of  it. 
West  of  the  ponds  on  the  latter  mountain  there  are  scattered  exposures  of 
compact  and  also  of  friable  beds  of  light-gray  tuff,  composed  of  small  frag- 
ments of  horubleude-mica-andesite  and  hornblende-andesite,  with  larger 
rounded  and  subaugular  pieces  of  the  same  kinds  of  rock  (1481,  1482). 

Just  west  of  the  saddle  east  of  Pj'-ramid  Peak  the  basalt  is  exposed 
with  overlying  beds  composed  of  fine  grains  of  hornblende-mica-andesite, 
acting  as  a  cement  for  fragments  and  rounded  masses  of  vesicular  basalt, 
similar  to  the  basalt  of  the  neighborhood.  Above  this  the  pyramidal 
mountain  is  formed  of  light-colored  andesitic  breccia  and  tuff  to  its  summit. 
The  whole  mass  is  exposed  in  bold  escarpment,  and  consists  of  nearly  hori- 
zontal beds  of  tuff  and  breccia,  with  layers  of  large  fragments  that  are 
subangular,  rounded,  and  also  angular.  There  is  great  variety  of  color 
and  habit  in  the  andesite.  The  greater  part  is  hornblende-andesite,  some  is 
hornblende-mica-andesite,  and  some  pyroxene-andesite ;  portions  of  it  are 
dense  and  compact,  other  portions  porous.  The  beds  are  brown  and  gray, 
some  being  very  thick  without  distinct  bedding.     At  the  southern  end  of 


282  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK, 

the  escarpment  there  is  much  gray  ash  with  leaf  impressions  (1478,  1479, 
1480). 

Similar  liarht-colored  breccia  extends  south  and  west  and  forms  the 
upper  part  of  the  mountain  ridge  through  Cathedral  Peak,  lying  between 
Cold  Creek  and  Jones  Creek.  It  constitutes  the  main  mass  of  Mount 
Chittenden  and  the  low  mountains  north  to  Raven  Creek,  and  beyond  to 
Pelican  Cone  and  the  ridge  west  (1160,  1161). 

In  these  low  mountains  the  character  of  the  andesites  constituting  the 
breccia  varies  considerably,  and  acid  and  basic  andesites  are  often 
intimately  mingled,  many  fragments  being  hornblendic,  while  others  are 
wholly  pyroxenic.  However,  it  is  evident  in  numerous  places  that  the 
more  siliceous  and  hornblendic  andesites  predominate  in  the  lower  parts  of 
the  mass,  and  are  overlain  by  distinctly  later  accumulations  of  basic  andesite. 
Thus,  at  the  falls  on  Raven  Creek,  at  about  the  8,200-foot  contour  of  the 
map,  and  within  a  short  distance  of  the  limits  of  the  older  basalt,  hornblende- 
andesitic  breccia  is  exposed  in  indurated  beds  which  cany  rounded  bowlders 
of  the  same  rock.  It  is  also  found  iimnediately  south  of  this  point  on  the 
summit  of  the  ridge,  where  it  is  capped  by  dai'k-colored  basic  breccia, 
which  is  well  bedded  in  places. 

On  the  southern  side  of  the  meadow  at  the  head  of  Mist  Creek  and 
near  the  limits  of  the  older  basalt,  compact  breccia  of  hornblende-andesite 
is  exposed  in  such  a  manner  as  evidently  to  be  over  the  basalt,  although  an 
immediate  contact  was  not  discovered.  Similar  breccia,  not  so  indurated, 
however,  forms  the  ridge  south  of  this  locality.  Many  of  the  fragments 
are  hght  colored,  with  phenocrysts  of  feldspar  and  hornblende;  others  are 
darker,  have  less  noticeable  phenocrysts,  and  are  more  pyroxenic  (1483). 
At  the  knob  about  the  middle  of  this  ridge  the  hornblendic  breccia  is 
capped  by  a  remnant  of  dark-red  basic  breccia,  the  line  of  contact  between 
the  two  being  plainly  visible  (1484).  Similar  relations  exist  between  horn- 
blendic breccia  and  basic  breccia  on  the  ridge  across  the  head  of  Mist  and 
Cold  creeks  (1485,  1486).  The  various  altitudes  at  which  the  overlying 
basic  breccia  is  found  indicate  a  very  irregular  surface  for  the  previously 
accumulated  hornblendic  breccia. 

Tiie  breccia  west  of  Raven  Creek  forms  the  mass  of  Porcupine  Cone, 
which  is  hornblende-pyroxene-andesite  at  its  summit  (1159),  mostly  light 
colored.     West  of  the  mud  springs  on  Pelican  Creek  similar  andesite  occurs, 


ACID  BKECOIA  OF  MOUNT  CHITTENDEN.  283 

that  on  the  top  of  the  ridge  bein}^-  liornblenfle-mica-andcsite  (1160,  llGl). 
Hestin<;'  upon  the  <iTeat  sheet  of  basalt  on  top  of  31iiTor  riateau  are  areas  of 
andesitic  breccia  with  light-g'ray  tntf.  In  the  vicinity  of  Mirror  Lake  the 
light-gray  tuff  is  composed  of  bits  of  hornblende-mica-andesite  (1158),  bio- 
tite  not  being  veiy  plentiful.  Near  the  falls  on  Raven  Creek  the  tuff  is  gray 
and  fine  grained  (1157),  and  consists  of  j)articles  of  homblende-pyroxene- 
andesite  with  nuich  hornblende.  The  light-colored  breccia  of  Mount  Chit- 
tenden is  bedded  in  its  northern  spur,  and  can-ies  hornblende  and  some 
biotite.  The  andesitic  fragments  are  subangular;  many  are  glassy  and 
light  colored;  some  are  pyroxenic  and  vesicular  (1487).  Similar  breccia 
forms  the  western  spur  (1492).  At  the  northern  part  of  the  summit  of  the 
peak  the  breccia  contains  many  large  masses  of  hornblende-andesite  with 
abundant  hornblendes  (1488  to  1497).  The  acid  breccia  in  the  eastern 
base  of  the  niountain  summit  and  around  the  head  of  Jones  Creek  is  without 
bedding  and  occurs  in  irregularly  accumulated  bodies.  It  is  overlain  by 
dark-colored,  well-bedded  basic  breccia,  consisting  of  small  angular  frag- 
ments. This  is  distinct  along  the  crest  of  the  ridge  east  toward  Cathedral 
Peak  and  on  the  southern  slope  of  the  summit  of  Mount  Chittenden  and 
along  the  crest  of  the  ridge  to  the  south  and  southeast.  A  broad  dike  of 
hornblende-andesite-porphyry  cuto  the  southern  summit  of  Mount  Chitten- 
den, and  will  be  described  with  other  dike  rocks. 

The  character  of  the  upper  basic  breccia  is  basaltic  on  the  summit  of 
Mount  Chittenden  (1504  to  1507),  without  prominent  pheuocrysts.  Farther 
south,  beyond  the  pass,  it  is  dark  pyroxene-andesite  (1514).  The  under- 
lying unbedded  breccia  at  the  top  of  tlie  ridge  south  of  Mount  Chittenden 
is  mostly  pyroxene-andesite  (1513,  1515)  with  little  or  no  hornblende.  It 
extends  down  the  long  spur  westward  to  Lake  Butte,  where  it  overlies  mas- 
sive hornblende-mica-dacite  (1509,  1510).  This  rock  is  light  colored,  gray 
and  red,  with  abundant  small  phenocrysts  of  quartz,  feldspar,  hornblende, 
and  biotite.  It  is  extremely  porous  and  appears  to  have  been  a  surficial 
lava. 

Homblende-andesitic  breccia  forms  the  ridge  aroinid  the  head  of  Crow 
Creek  to  Avalanche  Peak  and  its  western  spur,  which  lies  north  of  Clear 
Creek.  Just  north  of  Avalanche  Peak  the  breccia  is  dark  colored  and 
hornblendic,  without  bedding,  and  carries  large  blocks  of  hornblende- 
andesite  from  3  to  8  feet  long  (1511).     Northward  it  passes  into  lighter- 


284  GEOLOGY' OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

colored  breccia.  The  uorthern  face  of  Avalanche  Peak  is  composed  of 
uubedded  breccia,  while  the  breccia  of  the  northwestern  spur  is  bedded. 
At  the  northern  end  of  the  sunmiit  of  the  peak  it  is  variegated  and  full  of 
hornblende  phenocrysts  (1516).  Honiblende-andesitic  breccia  forms  the 
main  mass  of  the  peak  southeast  of  Avalanche  Peak,  and  extends  along  the 
crest  of  the  mountain  ridge  eastward  between  Crow  and  Middle  creeks. 
Here  it  rests  upon  the  basalt  sheets  already  mentioned.  South  of  the  peak 
on  this  ridge,  1|  miles  west  of  the  one  hundred  and  tenth  meridian,  it  is 
well  exposed  in  bare  bluffs  and  spurs.  It  is  light-colored,  variegated,  and 
well-bedded  breccia,  mostly  hornblendic,  some  fragments  having  abundant 
pyroxene  phenocrysts  (1528,  1529). 

It  is  ovei-lain  by  massive  laminated  andesite,  which  is  rudely  columnar, 
and  forms  the  high  peak  just  mentioned.  This  mass  was  undoubtedly  a 
surficial  flow  over  an  uneven  surface  of  breccia  which  sloped  to  the  north 
and  also  to  the  south  at  this  point.  The  mass  is  at  present  about  400  feet 
thick,  and  at  its  base  is  dense,  gray,  and  crystalline,  with  no  prominent 
phenocrysts  (1614).  Farther  east  on  the  crest  of  the  ridge,  and  400  feet 
lower,  the  same  massive  andesite  forms  a  capping  to  the  breccia.  It  is 
laminated  and  finely  columnar,  having  large  vertical  columns  in  the  middle, 
and  smaller  ones  beneath,  with  irregular  parting  at  the  top  (1615).  Near 
it  the  breccia  consists  of  similar  pyroxene-andesite.  It  can  be  seen  from 
this  ridge  that  light-colored  breccia  forms  the  crest  of  the  ridge  north  of 
Crow  Creek  and  overlies  the  basic  breccia  and  basalt  sheets  constituting  the 
base  of  the  ridge.  The  light-colored  breccia  is  in  turn  capped  by  massive 
columnar  lava  on  Silver  Tip  Peak  and  on  the  next  peak  east.  Another 
remnant  of  massive  andesite  rests  on  the  breccia  at  the  head  of  Crow  Creek. 
It  is  about  200  feet  thick,  is  jointed  horizontally,  and  consists  of  hornblende- 
andesite  with  inconspicuous  phenocrj'sts  (1512). 

From  the  summit  of  the  ridge  north  of  Middle  Creek  it  also  appears 
that  the  mountain  mass  south  of  this  creek  is  similarly  constructed,  its 
lower  portion  of  basic  breccia,  with  basalt  sheets,  forming  high,  flat-topped 
spm-s  about  1,000  feet  above  the  valley.  The  upper  portion  consists  of  a 
high  ridge  of  light-colored,  well-bedded  breccia,  with  a  number  of  pinnacles 
on  its  northern  slopes,  the  pinnacles  being  beautifully  columnar,  dark-colored 
rock.  The  southwestern  end  of  the  upper  part  of  this  ridge  has  been  visited, 
and  consists  of  hght-colored  breccia  of  hornblende-andesite.     The  high  peak 


ACID  BRECCIA  OF  MOUNT  LANGFORD.  285 

1)11  tliis  ridj^e  4  iiiik's  uurtlit'iist  of  Blount  Lau^^fonl,  wlien  seen  from  the 
southwest,  appears  to  consist  of  indurated  light-colored  breccia,  traversed 
by  munerous  dikes.  The  same  ridge  a  mile  southwest  of  this  point  is  cut  by 
ten  dikes  within  a  distance  of  a  mile,  and  the  breccia  composing  the  ridge 
at  this  place  is  hornblende-andesite,  with  abundant  hornblende  in  most  cases, 
and  ofti'U  with  very  light-colored  tutF.  The  dikes  of  this  vicinity  will  be 
descril)eil  in  connection  with  the  great  system  of  dikes  at  Sylvan  Pass.  The 
light-colored  hornblendic  breccia,  which  has  been  traced  from  its  northern 
limit  in  the  neighborhood  of  Lamar  River,  continues  southward  as  far  as 
Mountain  Creek.  It  forms  the  mountain  ridges  around  the  southern  head 
of  Middle  Creek,  being  well  exposed  in  precipitous  amphitheaters  on  either 
side  of  Mount  Langford.  The  rude  bedding  of  the  mass  east  of  the  latter 
peak  is  about  horizontal.  The  character  of  the  breccia  in  places  is  very 
variable,  but  is  distinctly  hornblendic  (1634,  1635).  Mount  Langford  con- 
sists of  nearly  horizontal  beds  of  light-colored  breccia,  and  the  same  is 
true  of  its  northeastern  spur  and  the  ridge  west  to  Mount  Doane  and  north 
around  the  head  of  Middle  Creek.  On  the  summit  of  Mount  Langford  the 
breccia  consists  of  andesites  of  various  colors  and  habits,  with  small  or  large 
phenocrysts,  mostly  hornblendic.  Some  fragments  are  pyroxene-andesite 
(1632,  1633).  On  the  west  slope  of  Mount  Doane,  above  the  saddle,  the 
light-colored  hornblende-andesitic  breccia  contains  masses  of  hornblende- 
mica-andesite,  very  light  gray  and  pink,  with  abundant  phenocrysts  (1636, 
1637).  This  breccia  also  forms  the  southern  base  of  Mount  Stevenson,  the 
bedding  being  about  horizontal. 

The  mountain  ridge  from  Mount  Stevenson  as  far  as  the  Yellowstone 
Lake  is  composed  of  dark-colored  breccia,  in  part  hornblendic,  but  mostly 
of  basic  audesite  (1623,  1624).  The  andesitic  breccia  in  the  ridge  between 
Rocky  and  Beaverdam  creeks  is  similar  to  that  of  Mount  Langford ;  light 
colored,  in  places  dark;  largely  composed  of  hornblende-andesites  of 
various  habits,  together  with  some  basic  pyroxene-andesites  (1625  to  1631 
and  1447  to  1449).  The  same  light-colored  breccia  forms  the  ridge  east  of 
Beaverdam  Creek,  from  the  stream  bed  to  its  summit,  except  in  the  peak  of 
Mount  Humphreys  and  that  northwest  of  it,  where  the  light-colored  breccia 
is  capped  by  dark  breccia.  Bold  escarpments  on  the  northwest  side  of  the 
last-mentioned  mountain  exhibit  nearly  horizontal  beds  of  light  breccia 
overlain  by  similarly  bedded  dark  breccia,  the  bedding  of  the  two  being 


286  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

continuous  and  not  interrupted.  Occasionally  one  passes  into  the  other 
horizontally  near  the  line  of  contact.  The  dark  upper  breccia  consists  of 
basic  andesites  with  more  or  less  hornblende  in  phenocrysts.  The  greater 
number  are  very  dark,  with  minute  phenocrysts  of  feldspar  and  pyroxene 
(1638,  1639). 

Light-colored  breccia  forms  the  ridge  southwest  of  this  mountain, 
through  Coulter  Peak,  being  overlain  along  the  crest  by  a  horizontal  layer 
of  basic  breccia.  The  light-colored  breccia  passes  beneath  basic  breccia  at 
the  eastern  base  of  the  peak  south  of  Beaverdam  Creek,  the  lower  breccia 
being  pink  and  hornblendic,  the  upper  breccia  dark  colored  and  pyroxenic, 
with  a  little  hornblende  and  some  olivine  (1642,  1643).  It  is  distinctly 
bedded,  and  dips  about  20°  W.  At  the  head  of  the  south  fork  of  Beaver- 
dam Creek  the  light-colored  breccia  overlies  two  superimposed  sheets  of 
basalt,  over  which  is  a  deposit  of  trachytic  breccia,  already  referred  to.  The 
petrographical  character  of  these  basalts  and  the  trachyte,  as  well  as  their 
D-eological  position  with  respect  to  the  hornblende-andesite,  relates  them 
to  the  older  basaltic  period  of  the  Crandall  volcano,  though  they  probably 
were  emptied  from  some  other  center. 

The  light-colored  breccia  continues  around  the  eastern  head  of  Trappers 
Creek,  from  Mount  Humphreys  to  Table  Mountain  and  the  Turret.  At 
the  head  of  Mountain  Creek,  northwest  of  Eagle  Peak,  the  light-colored 
breccia  consists  of  light-gray  tuff  and  various-sized  fragments  of  horn- 
blende-andesite (1655  to  1660).  These  andesites  differ  in  color  and  habit, 
a  few  having  large  phenocrysts  of  hornblende.  There  is  occasionally  some 
mica.  In  places  the  rock  over  considerable  areas  is  all  of  the  same  mate- 
rial, though  apparently  brecciated,  solid  angular  masses  being  cemented 
by  crumbling  material  of  the  same  character.  There  are  also  large  masses 
of  somewhat  fissile  andesite,  but  nothing  resembling  intrusive  rock  in  place. 
Similar  andesite  forms  the  northern  spur  of  the  peak  at  the  head  of  Mountain 
Creek,  and  is  well  exposed  in  the  ridge  west  of  the  creek  to  Table  Mountain. 
It  is  but  rudely  bedded,  and  is  capped  by  well-bedded,  dark,  basic  breccia, 
which  forms  the  plateau  of  Table  Mountain.  It  is  also  overlain  by  patches 
of  basic  breccia  on  the  peak  at  the  head  of  Mountain  Creek,  and  passes 
beneath  the  mass  of  Eagle  Peak. 

At  the  southern  end  of  the  ridge  of  Table  Mountain  the  light-colored 
breccia  is  well  exposed.     It  is  like  that  farther  north  and  is  highly  varie- 


ACID  BRKCCIA  OF  MOUNTAIN  CKEEK.  287 

{jjiU'd  (lf)52  to  1654).  It  carries  lar<?e  inasses  of  audessite,  from  1  to  8  feet 
in  diameter.  The  beddiny  is  irregular — in  some  places  horizontal,  in  others 
dipping  20°  W.  It  is  topped  by  well-bedded  basic  breccia,  which  forms 
the  summit  of  the  Turret  and  covers  what  was  once  a  very  uneven  surface 
of  older  breccia.  The  light-colored  breccia  extends  down  to  the  valley  of 
Trappers  Creek  on  the  west  and  down  t<t  the  bott(im  of  Mountain  Creek  on 
the  east,  but  the  scmthern  end  of  the  ridg-e  for  1,000  feet  above  the  creek 
is  pyroxene-andesitic  breccia,  whose  relation  to  the  hornbleudic  breccia  was 
not  discovered. 

The  most  southern  exposure  of  what  has  been  definitely  recognized  as 
the  light-colored  hornblende-andesitic  breccia  is  in  the  vicinity  of  the  forks 
of  Mountain  Creek.  On  the  eastern  bank  of  the  north  fork  it  appears  to 
be  somewhat  indurated  in  places.  It  has  abundant  hornblendes,  and  some 
fragments  are  liornblende-biotite-andesite  (1661  to  16C6).  At  one  place  it 
consists  of  horizontal  layers  of  tuif  with  intercalated  layers  of  large  water- 
worn  and  rounded  fragments.  It  is  cut  by  small  bodies  of  intrusive  andes- 
ite.  It  forms  the  lower  end  of  the  spur  between  the  main  forks  of  the 
creek,  extending  up  it  to  a  point  500  feet  above  the  stream,  where  there  is 
an  exposure  of'  massive  hornblende-andesite,  porous  and  light  I'ed,  with 
some  large,  stout  hornblende  phenocrysts  and  segregations  of  red  horn- 
blende and  biotite  (1664,  1667).  In  this  vicinity  the  hornblendic  breccia  is 
overlain  by  dark-colored  basic  breccia,  the  superposition  being  shown  in  a 
number  of  places. 

South  of  this  point  no  distinct  accumulation  of  light-colored  hornblende- 
andesitic  breccia  has  been  observed.  It  is  possible,  however,  that  the  light- 
colored  layer  of  breccia  at  the  western  base  of  the  most  northern  prong  of 
The  Trident  may  represent  this  series  of  breccias.  It  is  not  separated  into 
thin  layers  or  beds,  but  weathers  into  a  massive  cliff  with  vertical  jjrisms. 
The  exposed  layer  is  over  100  feet  thick,  and  consists  of  light-colored  tuffs 
and  breccia,  with  andesitic  fragments  of  various  kinds.  They  are  mostly 
pyroxene-andesite,  but  many  carry  a  little  hornblende  and  others  a  little 
mica,  while  some  are  decidedly  hornblendic,  as  is  also  the  light-gray  tuff 
(1683,  1684).  This  layer  is  overlain  by  distinctly  bedded,  dark-colored 
breccia,  which  continues  up  to  the  summit  of  The  Trident. 

The  tuff-breccia  and  occasional  lava  flows  that  have  just  been  described 
consist  of  andesites,  for  the  most  part  light  colored  and  hornblendic.     By  far 


288  GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

the  larger  number  of  rocks  are  hornblende-pyroxene-andesites.  With  these 
are  intimately  mingled  hornblende-andesites  and  hornblende-mica-andesites, 
and  in  a  few  instances  dacites.  In  some  places  pyroxene-audesites  are 
abundant,  so  that  there  is  a  transition  into  the  overlying  basic  breccia.  In 
fact,  a  distinction  between  the  two  is  hardly  possible  except  in  a  broad  way, 
the  upper  breccia  being  prevailingh'  dark  colored,  and  the  predominant 
kinds  of  rock  being  pyroxene-andesite  and  basaltic  varieties,  with  basalt, 
and  much  less  hornblende-pyroxene-andesite. 

In  the  acid  Ijreccia  there  are  places  where  fragments  of  basaltic  andes- 
ite  occur  sparingly.  Such  a  mingling  of  varieties  is  nati;ral  because  of  the 
occurrence  t)f  this  breccia  iipon  the  flanks  of  volcanoes  which  are  composed 
of  basic  andesites  and  basalts.  Curiously  enough,  there  is  less  mingling 
than  might  be  expected,  and  the  contrast  between  the  underlying  basalts 
and  the  overlying  acid  breccia  is  well  mark  id  in  many  places.  The 
uncei-tainty  of  limits  and  the  transitional  character  of  the  breccia  are  most 
marked  between  this  upjjer  acid  breccia  and  the  overlying  upper  basic  breccia. 

In  describing  the  microscopical  characters  of  these  rocks,  it  seems  best 
to  follow  a  mineralogical  sequence,  rather  than  to  treat  the  rocks  in  the 
order  of  their  relative  abundance.  In  the  first  case  the  order  would  be: 
Dacite,  hornblende-mica-andesite,  hornblende-andesite,  hornblende-pvrox- 
ene-andesite,  pyroxene-andesite  (basaltic  andesite). 

Dacite. — The  only  rocks  belonging  to  this  terrane  that  are  clearly  dacite 
occur  in  two  localities  some  distance  apart:  Lake  Butte,  on  the  northeast 
shore  of  Yellowstone  Lake,  and  the  north,  base  of  Mount  Doane.  At  the 
first  locality  the  rock  is  massive,  and  is  exposed  for  only  a  short  distance, 
so  that  the  geological  character  of  the  mass  is  not  evident.  It  was 
probably  a  lava  flow  of  considerable  thickness,  for  the  sections  examined 
microscopically  are  holocrystalline.  The  rock  is  light  colored,  gray  and 
red,  and  extremely  porous,  but  not  pumiceous,  and  has  abundant  small 
phenocrysts  of  quartz,  feldspar,  hornblende,  and  biotite.  The  quartzes  are 
first  recognized  under  the  microscope,  when  they  are  found  to  be  very 
abundant.  The}'  are  partly  idiomorphic,  in  double  six-sided  pyramids, 
more  or  less  rounded.  They  contain,  as  inclusions,  lumps  of  glassy 
groundmass,  colorless  glass  in  pyramidal  cavities,  crystals  of  biotite,  and 
the  other  mineral  constituents  of  the  rock.  In  some  cases  rhombohedral 
cleavage  is  noticeable. 


DACITES  OF  ABSAROKA  RANGE.  289 

Till'  fi'ldspar  plieiiocrysts  arc  all  polysynthetic  twins,  and  are  lime- 
soda  feldspars,  some  itt"  which  exhibit  synnnetrical  extinction  angles  indi- 
cating labradorite,  but  others  appear  to  belong  to  more  alkaline  species. 
Zonal  structure  is  highly  develojied.  Inclusions  are  not  alnmdant,  and 
consist  of  occasional  crystals  of  biotite,  hornblende,  apatite,  zircon,  and 
mag'netite.  The  biotite,  which  is  abundant,  is  in  six-sided  plates,  and  also 
in  relatively  thick  crystals,  occasionally  the  thickness  being  greater  than 
the  width.  Its  color  is  dark  brown  in  thin  cleavage  plates,  and  strongly 
pleochroic  in  sections  perpendicular  to  the  cleavage,  bemg  pale  yellow  for 
light  vibrating  parallel  to  tl,  and  almost  opaque  for  that  at  right  angles  to 
this  direction.  In  places  the  lamellae  of  a  crystal  are  bent  at  one  end 
where  they  ajjproach  another  phenocryst,  indicating  the  forcible  crowding 
of  these  crystals  during  the  movement  of  the  magma  before  solidification. 
Inclusions  of  minute  apatite  crystals  are  common;  those  of  magnetite  and 
zircon  less  so.  The  hornblende  is  less  abundant  than  biotite,  and  is  green, 
with  a  tinge  of  brown,  with  marked  pleochroism,  pale  brown  ||  a,  brownish 
green  ||  Ij,  strong  green  ||  c.  Crystal  forms  are  seldom  observed,  except  in 
the  prism  zone,  where  the  unit  prism  predominates,  and  both  pinacoids 
may  be  present.  Often  the  outline  is  very  irregular.  Inclusions  of  biotite 
occur,  and  sometimes  apatite  and  magnetite.  It  is  a  later  crystallization 
than  biotite.  Apatite,  magnetite,  and  zircon  are  present  in  their  usual 
forms. 

The  grouudmass  is  holocrystalline,  very  fine  grained,  apparently 
microgranular,  but  the  indistinct  grains  when  highly  magnified  are  found 
to  have  a  micropoikilitic  structure — that  is,  they  consist  of  quartz  cement 
and  feldspar  microlites.  There  is  also  a  much  smaller  amount  of  mao-netite 
in  minute  crystals,  and  some  shreds  of  biotite. 

The  dacite  found  in  fragments  in  the  breccia  at  the  base  of  Mount 
Doane  (1637)  is  glassy  and  pumiceous,  with  abundant  minute  phenocrysts 
of  feldspar,  quartz,  and  hornblende,  and  less  biotite.  These  crystals  are 
nearly  all  idiomorphie,  except  when  in  fragments;  or  in  the  case  of  quartz, 
when  rounded.  Tlie  quartzes  contain  numerous  inclusions  of  colorless  glass 
with  gas  bubble  and  surrounding  strain  phenomena.  Other  inclusions  are 
rare.  The  feldspars  are  plagioclase,  probably  labradorite.  They  have  beau- 
tiful zonal  structure  and  frequent  glass  inclusions.  Minute  prisms  of  apatite 
and  crystals  of  the  other  constituents  are  sometimes  included.    Hornblende  is 

MON  XXSII,  PT  II 19 


290  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

abundant  and  dark  brown,  with  strong  absorption.  It  incloses  some  mag- 
netite, and  in  one  case  has  grown  around  augite.  Idiomorphic  and  broken 
crystals  occur  beside  one  another.  Biotite,  with  the  same  color  as  hornblende, 
is  less  abundant.  Some  crystals  are  idiomorphic;  others  are  bent  and 
ci-umpled  by  the  pressure  from  other  phenocrysts  prior  to  the  solidification 
of  the  mass.  Small  crystals  of  these  minerals,  almost  microscopic,  occur  in 
the  glassy  groundmass.  Magnetite,  apatite,  and  zircon  are  present  in  idio- 
morphic crystals.  The  groundmass  is  colorless  glass  with  a  relatively  small 
amount  of  very  minute  crystals.  It  is  pumiceous,  with  vesicles  more  or  less 
spherical,  or  drawn  out  into  spindle-shaped  tubes. 

Hornbiende-mica-andesites. — Tlic  varletlcs  of  tliesc  Tocks  are  microcrystalliue 
andesites  with  multitudes  of  minute  phenocrysts  of  plagioclase,  feldspar,  and 
hornblende,  and  fewer  of  biotite,  so  that  in  some  cases  they  might  be 
called  mica-bearing  hornblende-andesites.  In  thin  sections  the  hornblendes 
are  seen  to  be  diiferently  colored  in  different  rocks.  In  some  they  are  green 
and  brownish  green,  with  very  slight  border  of  magnetite  grains,  or  none  at 
all.  In  others  they  are  deep  chestnut  brown,  without  borders ;  in  still  others, 
strong  reddish  brown  with  pleochroism  from  orange  to  red  without  border, 
or  with  narrow  magnetite  margin.  Otherwise  they  are  alike,  having  similar 
forms  and  inclusions.  They  are  partly  idiomorphic.  Inclusions  are  not 
common.     Some  contain  numerous  glass  inclusions. 

Biotite  varies  also  in  color  and  is  easily  confused  with  hornblende  in 
some  of  the  rocks,  usually  having  the  same  colors  where  the  hornblende 
is  brown  and  red-brown ;  but  where  hornblende  is  green,  biotite  is  brown. 
Its  chief  inclusions  are  magnetite  and  apatite. 

Hvpersthene  and  augite  occur  in  only  a  few  rocks,  and  then  in  very 
small  crystals.  In  one  case  hypersthene  with  pronounced  pleochroism  has 
a  dark  border,  as  though  from  magmatic  action.  It  accompanies  red  horn- 
blendes. In  another  instance,  where  the  hornblendes  are  red,  the  few  small 
augites  are  nearly  colorless. 

The  plagioclase  is  toward  the  labradorite  part  of  the  series,  exhibiting 
rather  high  extinction  angles  and  having  forms  and  inclusions  similar  to 
those  of  the  plagioclases  of  the  dacites  just  described,  except  that  zonal 
sti'ucture  is  not  so  frequent,  being  most  pronounced  in  the  larger,  nearly 
equidimensional  crystals,  and  nearly  wanting  in  the  smaller,  nai'row 
rectangular  ones. 


ANDESITES  OF  ABSAROKA  RANGE.  291 

The  groundiuiiss  in  the  different  varieties  of  this  rock  varies  from 
microcryptocrystalline  and  microlitic  to  microcrystalline  with  micropoikilitic 
structure,  which  is  very  fine  grained,  the  structures  and  mineral  composi- 
tions being  typically  andesitic. 

Hornbiendcandesites. — The  habit  of  tlicse  rocks  is  generally  similar  to  that  of 
the  andesites  just  described — a  holocrystalliiie  groundmass  with  abundant 
minute  phenocrysts  of  feldspar  and  hornblende.  In  one  case  feldspar  pheno- 
crysts  are  wanting.  The  hornblendes  have  the  same  varieties  of  color  and 
other  characteristics  as  those  in  the  andesites  last  described.  In  most  of  the 
cases  studied  they  are  red.  Black  borders  occur  in  some  varieties,  but  with 
no  special  connection  with  any  particular  microstructure  of  the  ground- 
mass.  Biotite  is  present  in  several  rocks  in  small  amounts.  Small  crystals 
of  pyroxene  are  rare.  The  feldspar  phenocrysts  are  similar  to  those 
described  in  the  hornblende-mica-andesites.  The  groundmass  structures 
ai"e  also  similar — holocrvstalline  and  microlitic,  with  andesitic  habit. 

Hornbiende-pyroxene-andesite. — The  101  tliiu  scctious  of  this  klud  of  andesite 
which  were  studied  exhibit  a  range  of  mineral  composition  from  rocks  with 
much  feiTomagnesian  phenocrysts  to  others  with  few,  and  from  varieties 
with  much  hornblende  and  little  pyroxene,  which  are  closely  connected  with 
hornblende-andesite,  to  those  with  more  pyroxene  than  hornblende,  which 
might  be  classed  as  hornblende-bearing  pyroxene-andesites.  The  ground- 
mass  also  differs  greatly  in  various  rocks,  and  the  amount,  size,  and  shape  of 
the  feldspar  phenocrysts  are  equally  variable.  In  general,  however,  the 
habit  is  like  that  of  the  rocks  just  described — a  groundmass  crowded  with 
small  phenocrysts.  The  actual  character  of  the  groundmass  can  be  dis- 
covered only  with  the  microscope.  It  is  glassy  and  microlitic  in  many  cases 
and  holocrystalline  in  others. 

The  feldspar  phenocrysts,  which  are  present  in  great  abundance,  are 
mostly  rectangular  and  elongated  in  thin  sections.  They  are  all  plagio- 
clase,  and,  like  those  before  described,  probably  labradorite.  But  there 
appears  to  be  some  variability  in  the  kinds,  and  some  small  crystals  exhibit 
extinction  angles  suggesting  anorthite  (33°).  Polysynthetic  twinning  is 
always  present  to  a  greater  or  less  extent,  and  zonal  structure  is  highly 
developed  in  some  crystals,  over  100  alternating  zones  of  light  and  shade 
having  been  counted  in  one  feldspar,  which  Avas  0.46  mm.  from  center  to 
margin,  the  average  width  of  a  zone  being  0.0002  of  an  inch.     In  some  cases 


292  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  zones  alternate  in  the  values  of  their  extinction  angles,  so  that  it  would 
seem  as  though  the  composition  of  the  feldspar  oscillated  between  narrow 
limits  from  the  center  outward.  In  other  cases  the  center  exhibits  a  higher 
angle  of  extinction  than  the  marginal  zones,  from  which  it  may  be  inferred 
that  the  composition  changed  interruptedly  from  the  center  outward.  The 
feldspars  are  sometimes  free  from  inclusions,  sometimes  crowded  with  glass 
inclusions,  or  these  may  be  arranged  in  zones.  Microscopic  crystals  of 
pyroxene,  apatite,  and  magnetite  are  also  included  in  some  feldspars. 

The  hornblende  is  like  that  in  the  varieties  of  andesite  just  described; 
not  often  idiomorphic,  except  in  the  prism  zone ;  frequently  with  dark  border, 
which  is  sometimes  broad  and  compact.  Often  the  border  consists  of  minute 
pyroxenes.  Sometimes  the  hornblende  is  surrounded  by  comparatively 
large  crystals  of  pyroxene,  magnetite,  and  feldspar,  the  aggregate  having 
an  irregular  outline  in  some  instances,  and  in  others  having  the  outward 
form  of  hornblende.  The  colors  are  red-brown,  brown,  and,  less  often, 
green.  Occasionally  the  color  varies  in  strength  zonally.  Hornblende 
incloses  both  augite  and  hypersthene  in  comparatively  large  crystals,  and 
also  !n  smaller  grains,  and  exhibits  the  same  relations  of  intercrystallization 
with  the  pyroxenes  which  exist  between  these  three  minerals  in  the  diorites 
of  Electric  Peak.  In  one  rock  (1652)  the  brown  hornblende  is  intimately 
intergrown  watli  plagioclase,  as  in  the  case  of  hypersthene  in  the  andesite 
lava  from  Mount  Hood,  Oregon.'  The  pyroxenes  are  angite  and  hyper- 
sthene, generally  in  almost  identical  small  crystals,  with  like  forms  in  the 
prismatic  zone — unit  prism  and  both  pinacoids,  together  with  flat  terminal 
faces.  The  cleavage  and  twinning  are  normal.  The}^  have  nearly  the  same 
color  in  thin  section— pale  green.  But  the  hypersthene  has  reddish  tones 
for  rays  vibrating  transversely  to  the  prismatic  axis  of  the  crystal.  They 
are  distinguished  only  by  the  differences  in  their  double  refraction  and 
their  extinction  angles,  measured  from  the  prism  axis.  Their  most  frequent 
inclusions  are  crystals  of  magnetite.     Rarely  they  inclose  red  hornblende. 

The  groundmass  of  most  of  the  hornblende-pyroxene-andesites  studied 
is  glassy  and  crowded  with  minute  microlites.  Often  these  are  so  close 
together  that  it  is  not  possible  to  say  whether  there  is  any  amorphous 
glassy  substance  between  them.     In  some  cases  it  is  evident  that  the  whole 

'Iddings,  J.  P.,  The  eruptive  rocks  of  Electric  Pealc  and  Sepulclire  Mountain,  etc.:   Twelfth 
Ann.  Kept.  U.'  S.  Geol.  Survey,  1892,  p.  612. 


ANDESITES  OF  AliSAKOKA  KANGE,  293 

mass  is  crystallized.  The  more  fjlassy  varieties  afford  the  best  opportunity 
for  observinj;  the  character  of  the  microlites.  For  this  reason  it  may  be  best 
to  begin  with  the  description  of  the  most  glassy  A'arieties.  Of  these,  some 
have  glass,  which  is  colorless  in  thin  section,  with  many  distinctly  crystal- 
lized microlites,  which,  however,  are  not  crowded  together.  The  microlites 
are  feldspar,  pyroxene,  and  magnetite.  The  feldspars  have  not  always  the 
same  habit.  In  some  varieties  of  the  rock  the  microscopic  feldspars  are 
rectangular,  square,  and  elongated,  with  lamellar  twinning,  both  albitic 
and  pericliuic,  the  symmetrical  extinction  angles  of  33°  to  35°  indicating 
anorthite.  They  range  in  size  from  the  most  minute  crystals  to  those  0.6  mm. 
long.  They  are  at  times  indented  at  the  ends.  In  other  varieties  of  the 
rock  the  microlites  of  feldspar  are  parti}'  thin  tabular  crystals,  sometimes 
crossing  one  another  in  Carlsbad  twinning  position.  They  are  lime-soda 
feldspars  yielding  lath-shaped  cross  section.  In  the  glassiest  rocks  the  feld- 
spars have  the  most  abundant  glass  inclusions,  which  occur  even  in  micro- 
scopic crystals,  although  the  smallest  feldspars  are  quite  free  from  inclusions. 

The  pyroxene  microlites,  like  those  of  feldspar,  range  in  size  from  the 
minutest  to  those  that  might  be  called  small  phenocrysts.  Augite  and 
hypersthene  are  both  present,  but  in  some  cases  hypersthene  is  the  prevail- 
ing species.  Both  pyroxenes  occur  in  prisms,  sometimes  stout,  sometimes 
slender,  occasionally  very  thin.  They  are  often  cracked  across  as  with 
basal  parting,  the  pieces  of  crystal  slightly  sej^arated  in  some  cases.  These 
grade  into  cases  in  which  the  pyroxene  prisms  are  represented  by  a  line  of 
gi-ains  whose  distance  apart  equals  or  exceeds  the  thickness  of  the  grain. 
From  the  resemblance  of  these  grains  to  the  globulites  in  some  of  the 
glassy  groundmasses  it  is  probable  that  these  globulites  are  augite  to  a  con- 
sidei'able  extent. 

Magnetite  crystals  are  frequently  inclosed  in  the  jjyroxene  in  great 
numbers,  but  in  some  cases  they  are  nearly  free  from  them.  The  mag- 
netite crystals  are  idiomorphic  in  many  cases,  but  in  others  their  forms  are 
indistinct.  One  perfectly  developed  crystal  which  was  inclosed  in  a  feldsjjar 
had  the  form  of  a  dodecahedron  combined  with  an  octahedron.  Apatite 
occurs  in  minute  hexagonal  prisms. 

In  groundmasses  where  the  glass  is  crowded  with  microlites  their 
forms  appear  to  be  the  same,  but  on  account  of  their  frequent  superposition 
the  forms  are  not  so  easily  observed. 


294     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

In  some  glassy  varieties  the  glass  is  brown  in  very  thin  sections,  and 
the  microlites  of  colorless  feldspar  and  pale-green  augite  are  distinctly 
contrasted  with  the  glass.  In  other  parts  of  the  same  rock  the  pyroxene 
crystals,  small  and  large,  are  reddened  on  the  surface  and  have  a  red 
opaque  margin  or  incrustation,  the  smallest  crystals  being  reddened 
throughout,  the  large  ones  only  marginally.  In  these  parts  of  the  rock  the 
glass  is  more  often  colorless,  as  though  the  brown  pigment  had  been  segre- 
gated about  the  pyroxenes.  But  there  are  cases  where  reddened  pyroxenes 
occur  in  brown  glass.  In  one  rock  the  glass  is  yellow  and  orange  in  thin 
section,  and  the  pyroxenes  are  reddened  and  there  is  a  reddish  opaque 
border  to  many  crystals.  This  is  more  pronounced  about  the  hyperstheues 
than  about  the  augites.  Brown  and  yellow  glasses  grade  into  one  another 
in  one  rock.  One  variety  has  a  beautiful  brown  globulitic  glass  base,  with 
the  usual  microlites.  Another  groundmass  consists  of  colorless  glass, 
crowded  with  xerj  minute  thin  prisms  of  pyroxene,  feldspar,  and  magnet- 
ite. The  form  of  these  crystals  may  be  observed  when  a  thin  layer  of 
groundmass  wedges  out  over  a  large  crystal  of  feldspar.  In  thicker  layers 
the  groundmass  appears  as  a  gray  felt  of  these  crystals.  In  the  few  holo- 
crystalline  modifications  the  microstructure  seems  to  be  that  which  would 
be  caused  by  the  crystallization  of  the  feldspar  microlites  against  one 
another.  Their  outline  is  lost,  and  all  of  the  coloring  matter  of  the  glass 
base  is  concentrated  in  the  ferromagnesian  constituents.  Sometimes  these 
are  distinctly  formed  pyroxenes,  together  with  magnetite.  In  other  cases 
there  is  considerable  chloritic  or  serpentinous  material  scattered  among  the 
feldspars.  In  several  instances  the  groundmass  contains  amygdules  of 
what  appears  to  be  chalcedony,  sometimes  coating  and  inclosing  crystals 
of  tridymite.  The  chalcedony  accompanies  the  opalization  of  hypersthene, 
a  form  of  alteration  noticed  by  Kiich^  in  the  andesites  of  Colombia.  In 
general  the  rocks  collected  are  almost  free  from  decomposition  of  any  kind. 

pyroxene-andesite. — Tliesc  audcsitcs  havc  csseutially  the  same  habit  as  the 
hornblende-pyroxene-andesites,  but  are  darker  colored  as  a  whole.  The 
abundant  small  phenocrysts  are  lime-soda  feldspar,  hypersthene,  and  augite. 
In  a  few  cases  there  is  a  small  amount  of  hornblende  with  black  border,  or 

'  W.  Eeiss  and  A.  Stiibel.  Reisen  in  Siid-Amerilsa.  Geolosische  Studien  in  der  Repiiblik  Colom- 
bia. I.  Petrographie.  I.  Die  vullianischen  Gesteine.  Bearbeitet  von  Kichard  Kiicb.  Berlin,  1892. 
Reviewed  in  Jour.  Geol.,  Vol.  I,  No.  2, 1893,  pp.  164-175. 


PYROXENE  ANDESITES  OP  ABSAUOKA  KANGE.  295 

of  liornblendo  parainorplis.     '^Flie  fi^-i'oundmass  is   aplianitic  and  dark  gray 
or  black,  or  liglit  gray,  occasionally  red. 

In  thin  section  the  feldspar  plienocrysts  are  mostly  rectangular,  with 
polysynthetic  twinning  after  both  laws ;  relatively  strong  double  refraction 
iind  high  extinction  angles,  indicating  labradorite-anorthite.  Zonal  struc- 
tui-e  is  pronounced,  and  glass  inclusions  are  abundant,  the  larger  feldspars 
being  somotimcs  filled  with  them.  The  pyroxenes  are  hypersthene  and 
augite  in  variable  proi)ortions.  In  some  varieties  of  the  rock  hypersthene  is 
greatly  in  excess  of  augite,  and  is  distinctly  pleochroic.  It  occasionally 
fonus  small  aggregations  with  labradorite,  the  crystals  of  feldspar  project- 
ing radially  from  the  margin  of  the  aggregate.  Similar  aggregates  some- 
times surround  hornblende  plienocrysts.  Inclusions  of  magnetite  are 
common,  and  those  of  glass  less  frequent.  There  are  occasional  evidences 
of  the  nearly  synchronous  growth  of  the  pyroxene  and  feldspar,  crystals  of 
the  former  being  interrupted  in  their  growth  by  those  of  feldspar.  Rare 
cases  of  actual  synchronous  crystallization  resulting  in  mutual  intergrowth 
have  already  been  mentioned.  Augite  is  almost  identical  with  hypersthene 
in  its  modes  of  crystallization  and  association.  They  are  sometimes  inti- 
mately intergrown,  and  are  distinguishable  only  between  crossed  uicols. 
Zonal  structure  is  occasionally  noticeable  in  the  distribution  of  color,  and 
in  the  optical  properties,  the  color  varying  from  pale  green  to  brown  and 
reddish  brown.  In  most  cases  they  are  fresh  and  not  decomposed.  Rarely 
they  are  partly  altered  into  opal.  The  small  individuals  of  hornblende, 
usually  irregularly  outlined  and  with  magnetite  or  pyroxene  bordei",  are 
generall}'  reddish  brown.  Magnetite  and  apatite  are  the  same  as  in  the 
other  andesites,  but  are  somewhat  more  abundant. 

The  groundmass  structures  of  the  pyroxene-andesites  are  almost  identi- 
cal with  those  of  the  hornblende-pyroxene-andesites.  They  are  mostly 
microlitic,  with  prisms  of  plagioclase  and  pyroxene  and  crystals  of  magnet- 
ite. The  more  glassy  modifications  have  colorless  glass,  and  often  brown 
globulitic  glass  as  the  matrix.  Not  infrequently  the  glass  inclosed  in  the 
feldspar  plienocrysts  is  brown  while  that  in  the  surrounding-  groundmass  is 
coloi'less.  BroAvii  glass  is  rather  more  frequent  than  in  the  more  siliceous 
varieties  of  andesite.  Only  a  few  of  the  specimens  examined  were  holocrys- 
talline. 


29(3     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

Basaltic  andesite. — Qiie  of  tliG  fragmeuts  collected  has  a  peculiar  character. 
It  has  a  red  glassy  and  microlitic  grouudmass  with  abundant  small  pheuo- 
crysts,  in  habit  being  similar  to  the  rocks  just  described.  But  the  porphy- 
ritical  minerals  are  augite,  red  mica  with  variable  optic  angle,  numerous 
serpentinized  olivines,  some  red  hornblende,  and  very  few  plagioclase  feld- 
spars. There  are  numerous  microlites  of  plagioclase  in  the  groundmass. 
The  rock  is  a  more  magnesian  phase  of  the  andesitic  magma,  related  to 
homblende-pyroxene-andesite.  It  is  not  known  in  any  large  mass  in  the 
region,  although  it  must  have  existed  as  a  lava  flow  at  some  period  in  the 
history  of  the  volcanoes  of  this  range. 

Segregations  are  not  often  noticed,  partly  because  they  are  easily  over- 
looked in  the  breccia,  where  the  small  fragments  generally  appear  with 
slio'htlv  different  characters.  In  thfe  massive  bodies  associated  with  the 
breccia  segregations  sometimes  occur.  They  are  composed  of  crystals 
about  the  size  of  the  phenocrysts,  either  crystallized  together  in  a  hypidio- 
morphic  mass  of  plagioclase,  hornblende,  biotite,  and  pyroxene,  with 
magnetite,  or  combined  as  large  crystals,  with  smaller  ones  forming  a 
relatively  coarse-gi'ained  groundmass  between  (1652,  1667). 

IjAtb  basic  breccia. 

The  character  and  mode  of  occurrence  of  the  basic  breccia,  which 
overlies  the  light-colored  and  more  siliceous  breccia,  have  been  indicated 
in  the  paragraphs  describing  the  late  acid  breccia;  but  they  should  be 
restated  in  greater  detail.  In  the  vicinity  of  Mist  Creek  the  basic  breccia 
overlies  the  light-colored  breccia  in  several  places,  and  is  found  to  consist 
of  dark-colored  pyroxene-andesites,  sometimes  with  hornblende,  sometimes 
with  olivine,  or  both  (1484,  1486).  On  the  south  side  of  the  summit  of 
Mount  Chittenden,  and  on  the  ridges  east  and  south,  the  dark-colored  breccia 
forms  Avell-bedded  accumulations  whose  layers  are  nearly  horizontal  and 
overlie  irregularly  bedded  or  wholly  unbedded  light-colored  breccia.  The 
upper  breccia  is  composed  of  pyroxene-andesites,  with  more  or  less  olivine, 
and  occasionally  hornblende.  This  breccia  probably  extends  down  the 
ridge  to  Lake  Butte  (1504  to  1507  and  1514,  1515). 

In  the  vicinity  of  Mount  Humphreys  the  upper  basic  breccia  overlies 
the  light-colored  breccia  in  distinctly  bedded  accumulations  which  are 
nearly  horizontal.     The  breccia  consists  of  dark-colored  pyroxene-andesite, 


UJ 
■  (3 


O 


BASIC  BUECCIA  OF  MOUNTAIN  OKEEK.  297 

somotimos  witli  hornblende,  sometimes  with  ohvine  (1G3S,  1()39).  It  caps 
the  ridfj^e  to  the  southeast  and  forms  its  western  sj)ur  (1641,  1(J42),  and  also 
a  small  point  on  the  southern  spur  of  Coulter  Peak.  The  upper  basic 
breccia  becomes  thicker  and  more  extensive  about  the  southern  end  of  the 
area  of  earlier  breccia.  At  Mount  Humi^hreys  and  the  peak  northwest  it 
is  about  600  feet  thick,  while  on  Table  Mountain  and  the  Turret  it  is  about 
800  feet  thick.     It  constitutes  the  mass  of  Eagle  Peak. 

The  bi'eccia  on  the  sununit  of  Table  Mountain  is  dark  colored  and  is 
composed  of  comparatively  small  fragments  of  basaltic  andesite,  with  small 
phenocrysts  (1668).  The  layers  of  this  mass  dip  gently  toward  the  west. 
The  mass  of  Eagle  Peak,  however,  presents  a  wholly  different  aspect  (PI. 
XXXV).  The  breccia  forming  this  mountain  is  distinctly  bedded,  but  the 
layers  are  not  horizontal,  dipping  at  various  angles  and  forming  a  slight 
syncliue,  the  dip  being  to  the  southeast,  away  from  the  light-colored 
breccia  at  the  head  of  Mountain  Creek  and  toward  the  northwest  from  the 
southern  end  of  the  mountain.  The  breccia  is  more  slaggy  and  scoriaceous, 
with  less  tuff  than  the  beds  on  Table  Mountain,  and  the  mineralosrical 
character  of  the  rock  is  more  uniform.  It  is  dark  colored,  mostly  pyroxenic 
with  much  olivine,  and  in  places  carries  some  hornblende.  There  are  dense, 
poi'ous,  and  vesicular  modifications  of  the  rock  (1669  to  1676).  In  places 
it  has  been  partially  altered,  producing  layers  and  patches  which  are  bright 
red,  brown,  and  yellow,  with  purple,  lavender,  and  green.  The  alteration 
seems  to  have  followed  certain  layers,  but  was  not  confined  to  them.  That 
there  is  considerable  divergence  in  the  bedding  of  the  breccia  may  be  seen 
from  the  eastern  side  of  the  mountain.  The  lower  beds  dip  at  steeper  angles 
than  the  upper  ones,  the  general  dip  l)eing  to  the  northwest.  One  massive 
bed  was  observed  to  thin  out  upward  toward  the  southeast,  and  to  thicken 
and  separate  into  several  beds  toward  the  northwest. 

The  mountain  range  east  of  the  northeastern  branch  of  Mountain 
Creek  is  composed  of  steeply  dipping  layers  of  similar  dark  breccia,  in 
places  brightly  colored  by  decomposition.  The  dip  in  general  is  toAvard 
the  northwest.  The  high  northern  portion  of  this  range  is  composed  of 
nearly  horizontal  beds  of  dark  breccia.  North  of  this  range  the  mountains 
are  made  up  of  similar  breccia  in  nearly  horizontal  layers,  which  occa- 
sionally dip  steeply  toward  the  north,  and  thicken  in  the  steep  parts  of  the 
layers. 


298     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

Basic  breccia  overlies  the  earlier  breccia  on  the  spur  uoi-theast  of  the 
forks  of  Mountain  Creek,  and  forms  the  mountains  to  the  northeast.  It  is 
distinctly  bedded  in  places  in  horizontal  layers,  with  more  tuff  than  in  the 
breccia  of  Eag-le  Peak.  It  is  composed  of  pyroxene-andesites,  some  with 
abundant  small  phenocrysts  of  feldspar  and  pyroxene,  others  with  almost 
no  noticeable  phenocrysts.  Much  of  it  contains  olivine.  Only  a  very 
little  carries  hornblende  (1679  to  1683).  Similar  dark-colored  breccia 
forms  the  main  mass  of  The  Trident,  where  it  occurs  in  nearly  horizontal 
layers  or  beds.  These  horizontally  bedded  breccias  extend  south  to 
Thorofare  Creek,  and  west  across  the  canyon  of  the  upper  Yellowstone 
River,  and  form  Two  Ocean  Plateau. 

Two  Ocean  Plateau. — The  uiass  of  Two  Occau  Platcau  above  the  valley  of 
the  upper  Yellowstone  River  consists  of  dark-colored  andesitic  breccia  in 
nearly  horizontal  layers.  The  bedding  appears  much  more  regular  at  a 
distance  than  upon  close  inspection,  when  it  is  often  found  to  be  very 
irregular.  In  the  vicinity  of  Two  Ocean  Pass  the  laj'ers  of  bedding  dip 
about  6°  NE.  This  dipping  proves  that  there  has  been  a  change  of  position 
since  the  breccias  were  accumulated,  and  indicates  a  depression  or  faulting 
toward  the  east,  or  in  the  Absaroka  Range. 

Near  the  mouth  of  Mink  Creek,  and  south  of  it,  the  breccias  are  dark 
colored  and  basic  and  are  associated  with  flows  of  massive  basalt  with 
porphyritical  feldspar  and  augite,  resembling  those  at  Two  Ocean  Pass. 
Over  the  limestone  near  the  head  of  Pacific  Creek  there  is  basic  breccia  in 
the  stream  channel,  while  on  both  sides  of  the  valley  at  higher  altitudes  are 
flows  of  basalt,  which  cross  the  valley  just  west  of  the  divide.  These  sheets 
of  basalt  form  a  distinct  ledge  on  both  sides  of  the  valley,  which  varies  in 
thickness  from  200  to  400  feet,  and  is  rudely  columnar.  Owing  to  the 
peculiar  composition  of  these  basalts  they  have  been  classed  with  the  sho- 
shonites  from  other  parts  of  the  Park,  and  are  described  in  connection 
with  them.  Above  the  western  end  of  the  basalt  ledge,  in  the  assorted 
andesitic  breccia,  there  is  a  layer  of  unassorted  light-colored  tuff"  Avith 
large  phenocrysts  of  sauidine  and  small  biotites  (1723-1725).  There  are 
clay -like  lumps  through  it,  and  many  fragments  of  basic  andesite  or  basalt. 
It  is  overlain  by  basic  andesitic  breccia.  The  same  kind  of  tuff  is  exposed 
on  the  southern  side  of  Two  Ocean  Pass,  in  a  layer  about  30  feet  thick. 
Here  it  passes  upward  into  fine-grained  tuff,  which  is  gray  and  bedded. 


TWO  OCEAN  PLATEAU.  299 

This  passes  ii})  into  assorted  basic  andesitic  breccia,  in  the  h)wer  portions  of 
which  are  rounded  i'ra^inents  of  the  sanidine-bearing  tuff  or  breccia. 

In  the  escarpment  of  the  phiteau  west  of  Two  Ocean  Pass  the  h)wer 
part  of  the  breccia  contains  many  layers  that  are  distinctly  waterlaid  and 
assorted,  the  masses  of  andesite  being  more  or  less  rovxnded.  But  the 
upper  portion  is  true  breccia,  angular  and  unassorted.  On  the  southern 
side  of  Two  Ocean  Pass  the  lower  part  of  the  plateau  mass  consists  of 
assorted  breccia  which  in  places  shows  evidence  of  having  been  rearranged 
b>'  water  action.  Laj'crs  of  tine  sand  and  gravel  and  large  masses  alternate 
with  one  another,  but  the  bedding  is  decidedly  irregular.  The  layers  are 
not  of  uniform  thickness,  and  ai:e  in  places  cross  bedded.  This  condi- 
tion continues  for  about  1,000  feet  above  the  valley,  the  upper  1,000  feet 
consisting  of  true  breccia  without  waterlaid  layers.  Here,  as  elsewhere  in 
the  breccia,  there  are  evidences  of  the  former  existence  of  localized  bodies 
of  water.  The  matrix  is  light  colored,  with  angular  fragments  of  all  sizes 
up  to  those  6  feet  in  diameter.  The  andesites  vary  in'  character;  some 
are  dark,  others  light;  some  dense,  others  vesicular.  They  carry  plieno- 
crysts  of  feldspar  and  pjroxene,  with  occasional  hornblende  or  olivine. 
The  whole  mass  has  a  distinct  but  irregular  bedding,  clearly  seen  at  a 
distance.  The  surfaces  of  the  layers  are  rough  and  irregular.  They  are 
generally  denser  at  the  bottom  of  each,  so  that  the  top  of  each  weathers 
more  easily  and  causes  the  line  of  bedding  to  become  pronounced  in 
exposures.  Where  layers  ditfer  in  color  and  can  be  traced  for  any  distance, 
they  are  observed  to  thin  out  laterally,  and  are  not  persistent  for  long 
distances. 

Horizontally  bedded  breccias  form  the  plateau  ridges  about  Jay  Creek 
and  those  west  of  the  Yellowstone  River,  and  also  the  mountains  at  the 
head  of  Buffalo  Fork  of  the  Snake  River,  which  are  the  southern  extension 
of  this  region.  Here  they  have  a  slight  dip  to  the  northeast.  They  also 
form  the  body  of  Two  Ocean  Plateau,  and  are  ex^iosed  in  the  lateral 
canyons  cut  into  it  by  the  tributaries  of  the  Yellowstone.  From  Atlantic 
Creek  to  north  of  Lynx  Creek  the  petrographical  character  of  the  rocks  is 
the  same,  and  there  are  places  where  the  material  has  been  assorted  and 
rearranged  by  water  action.  But  the  great  bulk  of  the  material  is  purely 
subaerial  ejectamenta.  At  the  head  of  Lynx  Creek,  on  the  continental 
divide,  are  remnants  of  a  surficial  flow  of  basalt  which  extends  down  the 


300     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

present  vallej'  for  a  short  distance,  and  is  therefore  hiter  than  the  period 
in  which  the  valley  was  eroded.  The  basalt  is  light  gray  and  somewhat 
vesicular,  with  small  phenocrysts  of  olivine  (1734,  1735).  A  similar  basalt 
occm's  on  Chipmunk  Creek  (1736). 

A  small  hill  on  the  divide  between  Fox  Creek  and  Mink  Creek  is 
formed  of  a  massive  flow  of  pyroxene-andesite,  which  is  jointed  into  great 
slabs  and  is  thinly  fissile  in  places.  It  resembles  many  occurrences  of 
rhyolite.  It  is  partly  massive  and  vesicular,  and  is  light  gray,  with  small 
phenocrysts  of  feldspar  and  pyroxene  (1727).  It  carries  segregations  of 
feldspar  and  pyroxene,  and  has  cavities  containing  tridymite  (1726).  Other 
portions  of  the  same  lava  sheet  are  darker  and  denser  (1728,  1729,  1730). 
The  breccia  along  the  western  margin  of  the  plateau  is  basic,  and  in  places 
there  are  remnants  of  porphyritic  basalt.  At  the  southern  end  of  the  valley 
of  Fox  Creek  it  is  composed  of  fragments  of  basic  andesite  in  a  light-red 
matrix,  and  on  the  limestone  hills  east  of  the  mouth  of  Crooked  Creek  it  is 
also  basic. 

Isolated  areas  of  basic  andesitic  and  basaltic  breccia  occur  overlying 
very  irregular  surfaces  of  sedimentary  rocks  on  the  peak  south  of  Pinyon 
Peak,  in  the  valley  of  Coulter  Creek,  in  the  vicinity  of  the  northern  end 
of  the  Teton  Range,  on  Berry,  Boone,  and  Conant  creeks,  and  at  Birch 
Hills.  The  last  of  these  occurrences  are  described  in  connection  with  the 
general  geology  of  the  northern  end  of  the  Teton  Range  (Chapter  IV). 
Those  in  the  region  of  Coulter  and  Wolverine  creeks  and  Pinyon  Peak 
are  described  by  Mr.  Arnold  Hague  in  Chapter  V,  devoted  to  the  descrip- 
tive geology  of  Big  Game  Ridge  and  Huckleberry  Mountain. 

Of  116  specimens  from  the  upper  basic  breccia,  one-half  contain  olivine 
in  variable  amounts,  and  may  be  classed  as  basalt  and  basaltic  andesite ; 
the  other  half  are  free  from  it,  and  are  pyroxene-andesites  and  hornblende- 
pyroxene-andesites,  the  last-named  rocks  being  much  fewer  than  the  pyrox- 
ene-andesites. 

Hornblende-pyroxene-andesite. TllC     fcW      SJlCCimeUS     of     tllis     kiud      of     audesite 

which  were  studied  prove  to  be  glassy  microlitic  modifications,  some  with 
dark-brown  glass,  one  with  red  glass.  Reddish-brown  hornblende  with 
magnetite  border,  or  an  outer  zone  of  pyroxene,  magnetite,  and  plagioclase, 
is  the  usual  variety.  In  one  rock  brown  hornblendes  without  any  border 
of  foreign  material  occur  so  closely  associated  with  pyroxene  as  to  inclose 


I'YKOXENE-ANDKSITES.  301 

it  in  a  variety  of  ways.  Tlicv  form  a  narrow  zone  of  small  prisms  around 
a  larji^c  au^ite  in  one  instance,  and  in  another  case  liornljlende  contains 
small  grains  of  angite  as  inclusions.  It  is  also  intergrown  with  pyroxene 
in  the  manner  already  described  in  othi'r  occurrences. 

pyroxene-andesites. — 'I'he  jiyroxeiie-andcsites  of  the  late  basic  breccia  are 
quite  the  same  as  those  of  the  late  acid  breccia  just  described.  Most  of 
them  have  glass}'  microlitic  grounchnasses,  the  glass  being  brown  in  the 
majority  of  cases.  Some  have  holocrystalline  groundmasses.  The  habit 
of  most  of  the  modifications  is  that  jjroduced  b}"  abundant  small  plieuo- 
crysts  and  a  microlitic  groundmass.  In  some  cases  distinct  phenocrysts 
are  wanting,  but  there  are  many  microscopic  prismatic  feldspars  in  the 
groundmass,  usually  aiTanged  in  curving  parallel  lines,  nroducing  fluidal 
structure. 

In  a  few  rocks  these  rectangular  microscopic  feldspars  are  in  excess  of 
the  microlitic  groundmass.  In  the  holocrystalline  varieties  the  dark  color 
of  the  groundmass  gives  way  to  gray  shades.  The  degree  of  crystallization 
does  not  exceed  that  of  holocrystalline-microlitic  or  finely  microgranular. 
The  phenocrysts  are  lime-soda  feldspar,  hypersthene,  and  augite,  with  small 
crystals  of  magnetite.  Rarely  hornblende  or  olivine  is  present  in  small 
amounts. 

The  feldspars  are  labradorite-bytownite,  with  marked  twinning  and 
zonal  structure,  and  generally  rectangular  outline  in  cross  section.  Glass 
inclusions  are  frequent.  In  some  varieties  of  this  rock  the  feldspar  phe- 
nocrysts are  anorthite.  Hypersthene  and  augite  have  the  same  colors, 
forms,  and  microscopical  characters  as  in  the  pyroxene-andesites  already 
described.  In  some  cases  pale-yellowish  augites  are  twinned  on  the  ortho- 
pinacoid,  and,  being  cnt  so  as  to  exhibit  symmetrical  extinction  angles  on 
both  sides  of  the  twinning  plane,  furnish  an  inclination  of  the  bisectrix  a 
equal  to  42°  to  the  trace  of  the  twinning  plane,  indicating  hedenbergite  or 
augite.  Zonal  structure  is  occasionally  exhibited  between  crossed  nicols,  and 
sometimes  by  variations  in  color.  Glass  inclusions  are  often  present.  The 
pyroxenes  are  mostly  fresh  and  unaltered.  An  alteration  of  hypersthene  to 
pale-green  pleochroic  amphibole  is  sometimes  observed,  the  fibers  of  amphi- 
bole  lying  parallel  to  the  vertical  axis  of  the  hyijersthene.  A  narrow  opaque 
border  and  a  darker-colored  margin  are  sometimes  present.  Occasionally  a 
serpentinous  mass  is  included  and  suggests  the  former  presence  of  olivine. 


302  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  pyroxene-andesite  occurring  as  a  massive  lava  flow  west  of  the 
head  of  Mink  Creelc  lias  a  habit  somewhat  different  from  that  of  the 
pyroxene-andesites  already  described.  It  has  a  smaller  number  of  pheno- 
crysts,  which  are  labradorite,  distinctly  pleochroic  hypersthene,  and  augite, 
the  pyroxenes  being  more  prismatic  than  usual.  The  groundmass  when 
very  dense  is  globulitic  and  microlitic  glass,  which  is  dark  colored  where 
the  microlites  are  very  minute.  Through  it  ai-e  scattei'ed  long  prismatic 
microlites  of  hypersthene,  augite,  and  feldspar.  In  varieties  with  larger 
microlites  the  color  is  lighter,  and  it  is  seen  that  pyroxene  is  more  abundant 
than  feldspar;  magnetite  also  is  abundant.  Apatite  occurs  in  comparatively 
few  large  crystals,  Avith  brownish  color  and  distinct  pleochroism.  Tridy- 
mite  is  present  in  small  aggregates. 

Basaltic  andesite  and  basalt. — These  rocks  are  like  the  pyroxene-andesites  in 
habit,  both  megascopically  and  microscopically.  They  consist  of  an 
aphanitic  groundmass  witli  multitudes  of  small  phenocrysts  of  feldspar 
and  pyroxene  and  more  or  less  altered  olivine.  In  some  varieties  the 
phenocrysts  are  almost  absent,  or  are  of  microscopic  proportions.  The 
colors  of  the  rocks  are  darker  as  a  whole  than  those  of  most  of  the  andesites. 
Dark  grays  to  black  and  red  are  most  common.  Light  grays  occur.  Many 
of  the  rocks  are  porous  or  finely  vesicular. 

In  thin  sections  the  groundmasses  are  seen  to  be  glassy,  with  abundant 
microlites  of  feldspar,  pyroxene,  and  magnetite,  the  latter  minerals  being 
rather  more  abundant  than  in  the  j)yi'oxene-andesites,  and  being  equal  to, 
or  sometimes  more  numerous  than,  the  feldspar.s.  The  microlitic  pyroxenes 
appear  to  be  augite.  The  feldspars  are  lime-soda  feldspars,  apparently 
about  andesine-labradorite,  but  not  always  of  the  same  kind.  The  glass  is 
usually  brown  globulitic,  when  in  noticeable  amount.  Holocrystalline 
modifications  occur;  they  are  very  fine  grained  and  are  formed  by  the 
o-rowinsT  together  of  microlites.  Groundmasses  so  crowded  with  iron  oxide 
as  to  be  opaque,  even  in  very  thin  sections,  are  common. 

The  feldspar  phenocrysts  are  labradorite-bytownite,  in  some  rocks 
being  more  calcic  than  the  proportion  Aug  Ab,,  in  other  cases  having  the 
optical  properties  of  this  variety  of  labradorite.  The  forms  are  mostly 
rectangular  and  prismatic,  tabular  forms  being  common  in  some  rocks.  The 
twinning  is  according  to  albite,  pericline,  and  Carlsbad  laws,  usually  all  three 
combined;  occasionallv  only  two.     Zonal  structure  is  pronounced,  especially 


BASALTIC  ANDESITE  AND  BASALT.  303 

ill  those  sections  exliibitino-  little  polysyiithetic  twiiiiiing.  In  ii  few  instances 
there  is  a  central  core  of  feldspar,  first  recognized  between  crossed  nicols, 
and  this  is  invariably  more  calcic  than  the  marginal  feldspar.  Glass  inclu- 
sions are  the  same  as  in  the  feldspars  of  the  ])yroxene-aiidesites.  Con- 
temporaneous crystallization  with  pyroxene  is  occasionally  observed. 

The  pyroxene  phenocrysts  are  augite  in  nearly  all  the  rocks  in  which 
olivine  is  abundant.  In  a  few  cases  hypersthene  is  also  present,  but  in  smaller 
amount  than  augite.  Transitional  varieties  with  hypersthene  and  olivine  in 
reciprocally  varying  proportions  have  been  mentioned  in  connection  with 
the  rocks  in  other  parts  of  this  region.  The  augites  have  the  same  appear- 
ance and  characters  as  in  the  andesites.  The  same  is  true  of  the  hyper- 
sthene when  present.  Olivine  occurs  in  very  small  idiomorphic  crystals, 
yielding  rhombic  and  characteristic  six-sided  sections.  It  is  iu  most  cases 
wholly  altered  either  to  green  serpentine  or  to  the  red  and  orange  pseudo- 
morphs  which  often  result  from  weathering.  In  the  few  cases  where  olivine 
is  still  preserved  it  is  colorless  in  thin  section.  The  serpenthiization  is  quite 
normal.  Both  modes  of  alteration  are  frequent,  but  the  green  serpentiniza- 
tion  is  probably  more  common.  They  do  not  occur  by  the  side  of  one 
another  in  one  rock  section.  In  only  one  instance  was  anything  like  a 
combination  of  the  two  observed.  The  processes  appear  to  be  due  to  local 
causes,  for  it  is  found  that  all  the  varieties,  with  olivine,  that  were  collected 
at  any  one  locality  bear  the  same  kind  of  pseudomorphs. 

Occasionally  colorless  olivine  is  coated  with  opaque  iron  oxide,  which  is 
red  by  incident  light.  It  occurs  in  minute  grains  penetrating  the  crystal  in 
rows  normal  to  the  side  planes.  The  shape  of  the  grain  suggests  that  the 
original  oxide  was  magnetite.  In  cross  sections  the  coating  appears  as  an 
opaque  border  of  variable  width.     In  one  rock  olivine  is  replaced  by  calcite. 

The  irregular  and  amygdaloidal  cavities  in  these  rocks  are  sometimes 
filled  with  secondary  minerals,  of  which  chalcedony  and  hyalite  or  opal 
and  several  zeolites  are  the  commonest  kinds.  The  first  two  are  often 
associated  together,  chalcedony  coating  the  walls  of  the  cavity  in  a  spheru- 
litic  layer,  opal  filling  the  central  portion.  In  one  of  the  pyroxene- 
andesites  the  chalcedony  of  the  margin  passes  into  fibrous  or  platy  quartz, 
which  fills  the  center  of  the  amygdule,  the  two  being  continuous  optically 
as  well  as  in  substance.  In  some  sections  thi-ough  such  amygdules  the 
central  quartz  exhibits  undulatory  extinction,  not  very  unlike  that  produced 


304     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  FARK. 

in  quartz  by  dynamic  forces.  It  is,  liowever,  in  this  case  the  result  of 
ao-o-resrate  crvstalhzation.  Such  sections  exhibit  uniaxial  interference 
crosses  wliich  are  optically  positive.  The  aggregation  appears  to  be  made 
up  of  thin  hexagonal  plates,  parallel  to  the  basal  pinacoid.  The  aggrega- 
tion of  plates  into  spherical  masses  takes  place  in  tridymite,  as  is  well 
known.  Spherulitic  aggregations  being  only  modifications  of  spherical 
ones,  such  structures  may  be  produced  by  the  attempts  of  thin  plates  to 
form  spherical  clusters.  The  rods  would  then  be  at  right  angles  to  the 
vertical  axis  of  the  mineral — that  is,  the  apparent  fibers  would  be  parallel 
to  a,  the  direction  of  vibration  of  the  swiftest-traveling  ray.  The  lighter 
specific  gravity  of  chalcedony,  as  compared  with  quartz,  would  seem  to  be 
due  to  inclusions,  probably  of  hyaline  silica,  since  minute  inclusions  are 
observed  in  thin  section,  and  a  variable  percentage  of  water  is  found  upon 
chemical  analj^sis.  Opal  replaces  the  feldspars  in  a  few  of  the  rocks 
studied. 

Sometimes  the  amygdules  consist  of  minute  zeolites  with  very  low 
double  refraction  and  a  marked  pinacoidal  cleavage  with  parallel  extinc- 
tion. It  is  probably  heulandite.  The  spaces  between  these  crystals  are 
filled  with  a  colorless,  low-refracting  substance,  apparently  composed  of 
minute  spherules  or  plates,  resembling  tridymite.  But  the  whole  mass  is 
spherulitic,  with  delicately  fibrous  rods  that  are  optically  positive.  The 
double  refraction  is  low.  There  seems  to  be  no  structural  relation  between 
the  minute  spherules  and  the  spherulitic  structure.  One  appears  to  be 
subsequent  to  the  other.  The  chemical  character  of  this  substance  was  not 
discovered.  Similar  mineral  with  stronger  double  refraction  occurs  in 
other  varieties  of  the  rock.  Other  secondary  minerals,  probably  zeolites, 
are  present  in  a  few  cases  (1682,  1675). 

rHKES   AISTD   SURFICIAIi  FLOWS. 

VICINITY  OF  SYLVAN  PASS. 

Subsequent  to  the  accumulation  of  the  late  acid  and  basic  breccia  of 
the  Absaroka  Mountains  there  broke  out  a  series  of  eruptions  whose  center 
of  activity  was  in  the  vicinity  of  Sylvan  Lake.  In  this  neighborhood  the 
breccias  are  traversed  in  all  directions  by  dikes  of  rocks  which  have  a  wide 
range  of  composition  and  which  also  attained  great  variety  of  crystalline 
structure. 


DIKES  NEAU  SYLVAN  PASS.  305 

In  tlu'  vjilley  of  Sylvan  Pass  and  on  tlio  slopes  of  the  mountains  on 
both  sides  the  hreccius  have  been  hig'hly  indurated  by  tlu;  intrusion  of  dikes 
close  to  one  another,  and  of  larger  bodies  of  magma.  This  is  particularly 
the  case  on  the  southern  side  of  the  valley.  This  metamorphism  is  limited 
in  extent  north  and  south,  but  continues  a  greater  distance  east  and  west. 
The  induration  of  the  breccia  and  the  presence  of  massive  rocks  produce 
mountain  slopes  ver}-  different  in  character  from  those  of  the  breccias  of  the 
region.  The  indurated  and  massive  rocks  weather  in  small  angular  frag- 
ments that  form  long,  bare  talus  slopes,  giving  to  the  southern  flanks  of 
Avalanche  Peak  and  of  the  mountain  southeast  a  smooth,  light-colored 
appearance,  which  is  quite  distinctive. 

The  southern  slope  of  Avalanche  Peak  has  the  character  just  noted. 
It  consists  of  indurated  breccia  of  hornblende-andesite,  traversed  by  intru- 
sive bodies  of  horublende-mica-andesite  and  of  hornblende-andesite.  Some 
of  these  bodies  have  been  crushed  and  fractured  so  as  to  I'esemble  breccia 
in  places.  They  furnish  evidence  of  dynamic  movements.  One  body  of 
hornblende-mica-andesite  (1532),  whose  outline  is  obscured  by  talus,  is 
altered  considerably.  The  phenocrysts  of  mica  are  large,  as  are  also  some 
of  hornblende  and  feldspar  It  is  finer  grained  and  fissile  near  the  south- 
ern contact  wall,  and  is  distinctly  mottled  in  planes  parallel  to  this  contact, 
and  carries  inclosed  fragments  of  other  rocks.  The  southern  end  of  the 
summit  of  the  mountain  is  formed  of  a  broad  dike  of  hornblende- 
andesite  (1533),  compact  and  gray,  with  abundant  small  phenocrysts  of 
hornblende  and  feldspar.  The  trend  of  this  dike  is  east  and  west,  and  that 
of  three  or  four  others  cutting  the  siunmit  of  the  peak  is  northwesterly. 
These  are  hornblende-andesite.  Another  dike  on  this  summit,  trending 
south  and  north,  is  hornblende-mica-andesite  (1534).  It  is  greenish  g'ray 
and  dense,  Avith  a  multitude  of  small  phenocrysts — white  and  prominent 
feldspai's,  altered  hornblendes,  and  fresh  biotite. 

The  northern  end  of  the  summit  consists  of  massive  rock  with  horn- 
blende and  pyroxene  phenocrysts.  The  northern  mass  of  the  peak  is  com- 
posed of  chaotic  breccia  of  hornblende-andesite  not  specially  indurated. 
Six  dikes  cut  the  northwestern  spur,  five  having  a  general  east- west  trend, 
and  one,  lower  down,  a  north-south  trend.  Three  dikes  cut  the  north- 
eastern spur.     They  have  a  northeast  trend.     On  the  eastern  spur  there  are 

MON   XXXII,  PT   II ^20 


306     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

three  dikes  with  a  soiitherly  trend.  One  of  these  dikes  consists  of  horn- 
blende-andesite  with  many  phenocrysts  of  hornblende  and  feldspar.  The 
rock  is  colnmnar,  with  horizontal  prisms. 

In  the  gulch  west  of  Avalanche  Peak  the  breccia  of  hornblende- 
andesite  is  indurated,  and  is  cut  by  bodies  of  horublende-andesite  that  have 
been  much  fractui-ed  and  cracked.  Similar  indurated  breccia  forms  the 
ridge  west,  and  is  traversed  by  ten  or  more  dikes  of  hoi'nblende-andesite 
with  variable  trends,  mostly  north  and  south  or  northeasterly.  On  the 
west  end  of  this  ridge  are  other  dikes,  whose  trends  were  not  observed. 

Other  dikes  of  liornblende-andesite  cut  the  ridge  from  Avalanche  Peak 
to  Mount  Chittenden.  They  have  a  general  north-south  trend,  as  indicated 
on  the  map,  several  trending  northeast  and  one  east.  Dikes  may  be  seen 
cutting  the  southern  face  of  Silver  Tip  Peak.  At  the  head  of  Crow  Creek 
several  of  the  dikes  traverse  the  sheet  of  massive  hornblende-pyroxene- 
andesite,  cutting  it  in  different  directions. 

These  dikes  extend  into  the  head  of  Jones  Creek,  the  most  northerly 
intersecting  the  eastern  edge  of  the  summit  of  Mount  Chittenden.  Here 
this  dike  is  50  or  60  feet  wide,  is  horizontally  columnar,  and  trends  a  little 
east  of  north.  The  rock  is  hornblende-andesite  (1498  to  1600),  dense,  fine 
grained,  witli  abundant  small  phenocrysts  of  hornblende,  sometimes  in 
stellate  groups,  and  less  prominent  feldspar.  No  dikes  were  observed  in 
the  mountains  northeast  of  Mount  Chittenden,  or  in  those  in  the  vicinity 
of  Pyramid  Peak,  or  in  Castor  and  Pollux  peaks. 

In  the  region  of  Sylvan  Pass,  the  mountain  mass  of  Hoyt  Peak 
consists  of  indurated  breccia  of  hornblende-andesite  with  some  pyroxene- 
andesite.  It  is  traversed  in  various  directions  by  dikes,  some  trending 
northeast  and  east,  and  others  southeast.  Those  cutting  the  northern 
crest  of  the  mountain  are  mostly  hornblende-andesite.  They  are  from 
4  to  10  feet  wide,  and  in  one  instance  20  feet.  The  rock  of  the  20-foot 
dike  (1535)  is  dense,  light  gray,  with  a  hackly  fracture,  and  is  crowded 
with  small  phenocrysts  of  minute  feldspars  and  larger  hornblendes,  with  a 
very  little  mica.  One  of  the  andesite  dikes  is  very  fine  grained,  with  few 
phenocrysts.  The  dikes  on  the  south  slope  are  largely  covered  by  talus. 
Their  general  trend  is  toward  the  southeast.  Among  them,  near  the  bottom 
of  the  slope,  are  several  dikes  of  quartz-mica-dacite,  with  phenocrysts  of 
these  minerals.      Farther  down  the  slope,  just  east  of  the  divide,  there  is 


DIKES  NEAR  SYLVAN  PASS.  307 

an  intrusion  of  honiblende-mica-autlesito  (1545),  Avhich  is  dense  and  dark 
"■ray,  with  abundant  liexa<j-onal  plates  of  biotite,  numerous  feldspars,  and 
inconspicuous  altered  hornblendes. 

Immediately  north  of  the  ])ass  is  an  exposure  of  granite  (153G,  1538). 
It  is  massive  and  breaks  into  large  blocks.  The  exposure  is  about  75  feet 
hig-li  and  150  feet  long.  The  rock  is  fine  grained,  with  })orpliyritical 
biotites,  resembling  those  in  the  andesite  just  noticed,  but  less  immerous. 

Dikes  of  light-colored  andesite  cut  the  high  peak  east  of  Sylvan  Pass, 
which  is  composed  of  dark-colored  basic  breccia.  They  have  a  general 
trend  a  little  south  of  east,  and  are  found  traversing  the  valley  of  Middle 
Creek  in  the  same  direction.  Here  they  cut  the  older  basalts.  At  the 
upper  forks  of  this  creek,  a  short  distance  east  of  Sylvan  Pass,  there  is  a 
great  dike  of  hornblende-mica-dacite  (1546),  with  some  quartz  phenocrysts 
and  abundant  large  feldspars.  The  biotite  forms  comparatively  long  prisms, 
one  being  5  mm.  in  length.  They  taper  slightl)'  toward  the  ends.  The  horn- 
blende is  more  or  less  decomposed.  The  dike  is  80  feet  wide,  and  forms  a 
high  wall  on  the  southern  side  of  the  valley,  and  passes  across  the  south  fork 
of  the  stream.  It  is  almost  vertical,  with  slight  hade  to  the  north,  and  is 
distinctly  jointed  in  horizontal  prisms.  Parallel  to  this  is  a  smaller  dike  of 
compact  hornblende-mica-andesite  Avith  multitudes  of  minute  phenocrysts 
(1547).  The  breccia  in  the  immediate  vicinity  is  indurated.  Halfway 
down  Middle  Creek  on  the  north  side  are  two  dikes  of  dense  gi'ay  rock 
with  veiy  few  phenocrysts  of  hornblende  (1548,  1549).  They  have  an 
east-west  trend. 

At  Sylvan  Pass,  east  of  the  divide,  the  valley  is  filled  with  masses  of 
rock  from  the  dikes  and  breccia  on  either  side.  Some  of  the  dike  rocks  are 
dense  crystalline  andesite-porphyry,  with  abundant  thin  crystals  of  horn- 
blende (1538,  1539);  othei's  are  less  crystallized,  with  various  habits.  On 
the  south  side  of  the  pass  indurated  breccia,  cut  by  many  parallel  dikes  of 
andesite,  forms  almost  vertical  cliffs  500  feet  high.  Some  of  these  dikes  are 
dark  colored,  dense,  and  lithoidal,  with  comparatively  large  hornblende 
phenocrysts  (1540);  others  are  darker,  with  abundant,  though  not  so  promi- 
nent, phenocrysts  of  hornblende  (1541).  Some  are  light  gray  and  compact, 
with  extremely  few  phenocrysts,  while  some  are  altered  and  green,  with 
spots  of  epidote  (1542,  1543).  There  is,  however,  not  much  alteration 
noticeable  in  the  vicinity,  most  of   the  rocks  being  fresh.      The  slopes 


308  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

west  of  this  cliff  ou  the  south  side  of  the  valley  are  greatly  obscured  by  soil 
and  drift.  The  scattered  exposures  show  the  breccia  highly  indurated,  and 
a  more  crj'stalline  form  of  intrusive  rock.  The  coarsest-gi'ained  variety 
is  a  medium-grained  diorite  (1554),  which  was  not  found  in  place.  Several 
other  forms  of  diorite  are  found  in  the  morainal  accumulations  (1552,  1553); 
also  a  porphyritic  variety  (1 555)  with  hornblende  phenocrysts.  At  the  north 
base  of  Grizzly  Peak  fine-grained  diorite-poi'phyry,  Avith  small  phenocrysts 
(if  hornblende  and  some  biotite,  forms  a  large  body  extending  for  about  a 
mile  in  an  east-west  direction  (1550,  1551).     It  is  blue-gray  and  compact. 

A  broad  dike  of  liornblende-andesite,  75  feet  wide,  can  be  traced  for  a 
long  distance  up  the  northeast  spur  of  Grizzly  Peak.  It  trends  north  of 
east.  Along  the  crest  of  the  ridge  from  Grizzh'  Peak  to  Top  Notch  at 
least  16  dikes  have  been  observed,  trending  at  various  angles  toward  the 
southwest,  south,  and  southeast.  One  is  a  40-foot  dike  of  hornblende-mica- 
andesite  (155G)  trending  northea.st.  It  is  dark  gray,  with  abundant  pheno- 
crysts of  feldspar,  altered  hornblende,  and  fresli  biotite.  Five  othei's  are 
of  hornblende-andesite.  Dikes  also  cut  the  upjier  end  of  Signal  Ridge. 
On  the  saddle  west  of  Top  Notch  Peak  a  dike  of  hornblende-andesite, 
trending  northwest  and  southeast,  is  intersected  by  a  30-foot  dike  of  horn- 
blende-mica-andesite  (1557),  which  trends  N.  10°  E.  The  rock  is  dense 
and  dark  colored,  with  numerous  small  phenocrysts  of  feldspar,  decomposed 
hornblende,  and  fresh  biotite.  On  the  ridge  southeast  of  the  summit  of  Top 
Notch  Peak  there  are  two  dikes  of  hornblende-andesite  trending  S.  20°  E., 
which  appear  to  extend  across  the  head  of  Middle  Creek  in  a  southeasterly 
direction;  east  of  them,  on  the  spur  between  the  forks  of  this  creek,  are 
several  other  dikes  with  the  same  general  trend  toward  the  southeast.  The 
summit  of  Top  Notch  Peak  is  traversed  by  dikes  in  several  directions.  A 
25-foot  dike  of  hornblende-mica-andesite  (1558)  trends  S.  20°  E.  The  rock 
is  light  gi'ay,  and  is  filled  with  phenocrysts  of  feldspar,  biotite,  and  horn- 
blende, and  a  few  of  quartz.  Another  of  this  kind  of  andesite  trends  with 
the  ridge  of  the  summit.  A  dike  of  hornblende-andesite  east  of  the  summit 
trends  N.  15°  E.,  and  two  others  occur  northeast  of  the  summit. 

All  of  these  dike  rocks  are  holocrj-stalline  with  the  excejition  of  two, 
which  may  be  glassy  and  crowded  with  microlites  or  may  be  holocrystalline. 
When  studied  mici-oscopically  they  are  found  to  be,  one,  pyroxene-andesite 
with    paramoiphs    after   hornblende    (1499);    five,    hornblende-pyroxene- 


ANDESITIO  DIKE  ROOKS.  309 

aiulcsites  (1498,  1500,  lASS,  1540,  1541);  another,  the  sanie  with  a  little 
mica  (1535);  two,  honibleiule-pyroxeiie-andesite-porphyiy  (1538,  1539); 
two,  honibleude-andesito  with  possiljly  a  little  pyroxene  (1548,  1549); 
eight,  hornblende-mica-andesites  (1532,  1534,  1556,  1543,  1545,  1557, 
1558,  1547);  and  one,  dacite  (1546).  The  majority  of  them  are  thus  seen 
to  be  hornblende-pyroxene-andesites  and  hornblende-mica-andesites,  while 
more  basic  and  more  acid  varieties  are  comparatively  scarce. 

The  pyroxene-andesite  (1499)  which  is  a  dike  in  Mount  Chittenden 
is  holocrystalline  with  typical  pilotaxitic  microstructure,  j^roduced  by 
microlites  of  plagioclase,  augite,  altered  hypersthene,  and  magnetite.  The 
very  small  phenocrysts  are  labradorite,  augite,  and  hypersthene,  with 
ojiaque  paramorphs  after  hornblende,  which  sometimes  have  a  central 
portion  composed  of  pyroxene  and  magnetite.  The  hornblende-pyroxene- 
andesites  are  holocrystalline,  with  microstructures  ranging  from  pilotaxitic 
(1498,  1500)  in  the  dike  rock  at  the  summit  of  Mount  Chittenden,  and  in 
a  dike  on  the  south  side  of  Sylvan  Pass  (1540),  which  rocks  have  rather 
large  phenocrysts  of  hornblende,  through  those  that  are  slightly  micropoi- 
kilitic  (1533,  1535, 1541),  to  those  that  are  so  plainly  microcrystalline  as  to 
be  classed  as  andesite-porphyry  (1538,  1539).  In  these  latter  varieties 
quartz  is  recognizable  as  a  component  of  the  groundmass.  It  is  probably 
present  also  in  the  rocks  with  incipient  micropoikilitic  structure. 

The  phenocrysts  are  very  small  and  abundant,  and  vary  somewhat 
in  their  relative  proportions,  pyroxene  being  scarce  in  some  cases,  and 
biotite  being  present  in  small  amount  in  one  instance  (1535).  The 
feldspar,  which  is  abundant,  is  labradorite,  but  probably  of  different  com- 
positions, which  is  indicated  by  tlie  optical  properties.  Hornblende  is 
greenish  brown,  with  no  black  border,  but  in  a  few  cases  with  a  narrow 
border  of  magnetite  grains.  Intergrowth  with  augite  was  observed  in  one 
instance.  Augite  and  hypersthene  have  the  characteristics  common  to 
these  minerals  in  all  the  andesitic  rocks  of  this  region.  They  are  subordi- 
nate to  hornblende,  and  generally  in  smaller  crystals.  Magnetite  and  color- 
less apatite  in  small  crystals  may  be  classed  with  the  phenocrysts.  The 
rock  forming  a  narrow  dike  on  the  north  side  of  Middle  Creek,  halfway 
down  its  course,  has  a  quite  different  character  (1548,  1549).  It  consists 
almost  wholly  of  groundmass,  with  only  a  few  scattered  j)henocrysts  of 
greenish-brown  hornblende  and  lime-soda  feldspar.      The  groundmass  con- 


310     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

sists  of  twinned  prism  of  plagioclase  with  low  extinction  angles.  In  most 
cases  the  rectangular  cross  sections  exhibit  high  extinction  angles ;  there  is 
some  rectangulai",  nnstriated  feldspar  with  nearly  parallel  extinction,  which 
may  be  oligoclase  or  orthoclase,  besides  chloritized  jjyroxene  and  magnet- 
ite. The  hornblende-mica-andesites  are  holocrystalline,  with  groundmasses 
that  are  microlitic  and  microcrystalliue  in  some  cases  and  slightly  micro- 
poikiHtic  in  others  (1532,  1534,  1543,  1545, 1547,  1556,  1557,  1558).  The 
phenocrysts,  though  abundant,  are  inconspicuous  in  most  cases,  but 
are  prominent  in  a  few  rocks.  They  are  labradorite,  green  and  greenish- 
brown  hornblende,  and  brown  biotite.  Magnetite,  apatite,  and  zircon  are 
also  present.  Hornblende  is  completely  altered  to  chlorite,  calcite,  epidote, 
and  quartz  in  some  rocks,  the  biotite  being  unaltered.  The  latter  is  oftener 
unaltered.  The  dike  on  the  summit  of  Top  Notch  (1558)  is  very  fresh,  with 
abundant  biotite  and  hornblende,  and  also  some  phenocrysts  of  quartz, 
which  indicate  that  the  rock  is  possibly  a  dacite.  AUanite  is  jDresent  in 
chestnut-brown  crystals.  The  80-foot  dike  near  the  upper  forks  of  Middle 
Creek  (1546)  is  like  the  last,  and  contains  some  quartz  phenocrysts.  The 
groundmass  is  slightly  more  crystalline,  and  is  hypidiomorphic  granular, 
with  minute  idiomorphic  quartzes  and  feldspars  in  prisms  and  grains.  The 
feldspar  phenocrysts  are  andesine.     It  is  holocr3^stalli]ie  dacite. 

The  diorite-porphyries  found  at  the  base  of  the  north  side  of  Grizzly 
Peak  (1550,  1551,  1555)  have  about  the  same  habit  as  the  hornblende- 
mica-andesite  with  abundant  small  phenocrysts,  except  that  they  are  dis- 
tinctly more  crystalline.  The  largest  crystals  are  about  the  size  of  the 
phenocrysts  in  the  andesite — 1  or  2  mm.  long.  The  remainder  of  the  rock, 
however,  is  crystallized  into  relatively  large  grains  of  quartz  and  feldspar. 
In  thin  section  the  rocks  consist  of  idiomorphic  rectangular  crystals  of 
labradorite,  which  form  the  greater  part  of  the  rock.  With  variation  in 
the  amount  of  small  grains  of  quartz  and  feldspar  the  structure  grades  from 
that  of  diorite-porphyry  to  that  of  a  fine-grained  diorite.  The  large  body 
of  this  rock  found  in  places  may  properly  be  called  fine-gi"ained  diorite, 
slightly  porphyritic.  The  labradorite  has  probably  the  comjjosition  indi- 
cated by  Aui  Abi-  There  is  little  orthoclase  and  a  small  amount  of  quartz. 
Ferromagnesian  minerals  are  abundant,  and  are  more  or  less  completely 
altered  to  uralite  and  chlorite.  They  ai-e  brown  biotite,  brownish-green 
hornblende,  and  pyroxene.     Allanite,  epidote,  and  magnetite  are  present  in 


DIKES  SOUTH  OF  SYLVAN  PASS.  311 

siiiall  amouuts.  Coarser-yraiuod  modifications  occur  (ir)52  to  1554)  that  are 
fine-f^raiued  diorite,  the  average-sized  crystals  being  about  2  inin.  in  length. 
Tlu')'  consist  of  nearly  idioniorphic  labradorite,  very  little  quartz,  consider- 
able brown  biotite  intergrown  with  brown  hornblende,  and  uralitized 
pyroxene.  In  one  rock  (1554)  there  is  a  little  augite  still  unaltered. 
Apatite  is  abundant  in  long,  stout  prisms,  with  cross  fractures,  and  some- 
times bent  or  broken.  The  rocks  belong  to  the  group  of  mica-pyroxene- 
diorites,  and  are  similar  to  some  of  the  diorites  of  Electric  Peak. 

The  very  fine-grained  granite  or  granite-porphyry  (1536,  1537)  consists 
of  nearly  idioniorphic  crystals  of  labradorite  and  andesine,  about  1  mm. 
long,  with  smaller  grains  of  orthoclase  and  quartz,  besides  considerable 
biotite  and  magnetite;  also  small  apatites  and  zircon.  There  is  a  little  chlo- 
rite and  calcite.  It  is  a  question  whether  the  rock  might  not  be  more 
properly  classed  as  quartz-mica-diorite.  It  is  very  similar  to  the  quartz- 
mica-diorite  (321)  from  Electric  Peak,  which  has  67.54  per  cent  of  Si02, 
and  which  may  well  be  classed  as  granite. 

DIKES  SOUTH    AND    SOUTHEAST    OF    SYLVAN    PASS. 

South  and  southeast  of  the  neighborhood  of  Sylvan  Pass  there  are 
dikes  and  intrusions  and  surface  flows  of  massive  rocks  which  by  their 
composition  and  petrographical  habit,  as  well  as  by  their  mode  of  occur- 
rence, appear  to  belong  to  the  eruptions  we  have  just  been  describing.  It 
is  noticeable,  however,  that  they  differ  from  the  intrusive  rocks  in  the  imme- 
diate vicinity  of  Sylvan  Pass  in  the  degree  of  crystallization  attained  by 
the  groundmasses  of  the  rocks.  They  are  still  finer  grained.  A  number 
of  dikes  have  been  observed  along  the  ridge  southwest  of  the  headwaters  of 
Middle  Creek.  A  large  dike  cuts  the  southern  slope  of  the  ridge  between 
Mount  Doane  and  Mount  Langford,  and  trends  north-northwest  with  a  hade 
of  60°  NE.  It  is  about  300  feet  wide  in  its  lowest  exposure,  growing 
narrower  near  the  crest  of  the  ridge.  It  consists  of  hornblende-andesite 
(1559,  1560),  with  abundant  small  phenocrysts  of  hornblende  and  smaller 
feldspars  in  great  abundance.  The  groundmass  of  the  rock  is  light  gray 
and  lithoidal,  with  many  small  cavities  or  pores.  At  the  contact  it  is 
darker  colored.  In  the  center  of  the  dike  it  is  holocrystalline,  with  slight 
micropoikilitic  structure,  while  near  the  margin  it  is  almost  glassy,  with 
crowded  microlites,  though  in  places  even  here  it  is  holocrystalline.     The 


312  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

liornblende  is  greenish  brown.  The  feldspars  are  labradorite.  There  is  a 
little  augite  in  phenocrysts,  and  some  altered  h^^persthene  and  magnetite. 

On  the  peak  south  of  i\Iount  Langford  a  small  dike  trending  east  and 
west  consists  of  very  dark-colored  and  dense  hornblende-andesite,  with 
many  small  hornblende  phenocrysts  and  none  of  feldspar  (1561).  The 
groundmass  is  globulitic  glass  crowded  with  microlites  of  feldspar  and 
pyroxene.  There  fire  many  small  phenocrysts  of  augite,  besides  those  of 
greenish-ljrown  hornblende. 

The  dikes  cutting  the  ridge  east  of  the  south  fork  of  Middle  Creek 
have  a  general  trend  to  the  northwest,  but  vary  somewhat  and  intersect  one 
another.  They  may  be  seen  traversing  the  ridges  to  the  northwest  and  also 
to  the  southeast.  Other  dikes  were  observed  traversing  the  ridge  northeast 
of  the  farthest  point  visited,  and  it  is  probable  that  the  country  south  of 
Middle  Creek  is  filled  with  dikes,  but  none  have  been  mapped  in  that 
locality. 

The  most  northerly  dike  reached  on  the  ridge  in  question  is  about  20 
feet  wide,  and  trends  a  little  south  of  west,  with  steep  hade  to  the  north- 
west. It  is  liornblende-andesite  (1562),  compact  and  dark  purplish  graj^ 
with  prominent  johenocrysts  of  hornblende  and  white  feldspar.  It  s})lits 
in  plates  parallel  to  the  walls  of  the  dike.  The  groundmass  is  a  crowded 
mixture  of  feldspar  prisms,  brown  globulitic  particles,  and  magnetite  grains, 
and  is  possibly  glassy.  The  hornblende  is  green,  and  there  is  a  little  brown 
biotite.  The  feldspars  are  probably  labradorite.  Immediately  south  of 
this  dike  a  steeply  dipping  sheet  or  dike  of  hornblende-andesite  (1563, 
1564)  caps  the  ridge  for  a  distance  of  three-eighths  of  a  mile.  It  is  at 
present  from  20  to  50  feet  thick,  but  the  upper  wall  has  probably  been 
eroded.  The  dip  is  to  the  southeast.  At  the  northern  end  of  the  exposure 
it  is  relatively  dense  and  prismatic  and  light  gray;  at  the  southern  end  it 
is  more  porous,  or  almost  vesicular  and  fissile,  and  is  dark  gray  (1563).  At 
the  bottom  plane  of  contact  it  is  dense,  bluish  black,  and  glassy  (1564), 
is  rich  in  phenocrysts  of  hornblende,  with  smaller  feldspai-s,  and  carries 
scattered  segregations  of  coarsely  crystalline  hornblende  and  feldspar.  The 
lighter-colored  part  of  the  rock  mass  is  holocrystalline,  but  microlitic,  and 
slightly  granular  in  places.  In  the  darker  parts  it  is  pilotaxitic,  and  at  the 
margin  is  glassy,  consisting  of  beautiful  brown  globulitic  and  microlitic 
glass.     The  phenocrysts  are  alike  throughout — brown  hornblende,  labra- 


DIKES  AT  HEAD  OF  MIDDLE  GREEK.  313 

dorite,  probably  with  the  conipcisitidu  Ab,  An,,  and  a  litthi  augite  and 
niag-netite.  One  of  the  coarse-grained  segreg-ations,  or  simple  crystalli- 
zations, consists  of  labradorite  and  hornblende,  in  allotrioinorpliic  crystals 
1  nini.  in  diameter,  with  magnetite  and  apatite  in  irregularly  shaped  g-rains. 
The  feldspar  and  hornblende  have  the  same  characters  as  the  phenocrysts 
in  the  surrounding  andesite,  and  there  can  be  no  doubt  as  to  their  being' 
crystallizations  from  the  same  magma.  The  structure  is  granitic.  This 
sheet  is  cut  by  two  dikes  of  hornblende-andesite  (1565,  156fi),  15  and  20 
feet  wide,  that  trend  northwest.  They  are  i-ather  dense  and  slightly  vesic- 
ular, with  flattened  cavities,  are  light  gray,  and  carry  scattered  pheno- 
crysts of  hornblende  and  few  feldspars.  The  groundmass  is  pilotaxitic 
to  hyalopilitic  in  one  case,  and  holocrystalHne  with  prismatic  and  tabular 
feldspar  microlites  in  the  other.  The  phenocrysts  are  like  those  in  the 
andesites  ju.st  described.  South  of  the  inclined  sheet  are  two  small  dikes 
trending  northwest.  They  are  hornblende-andesite,  similar  to  the  last. 
Another  parallel  dike,  15  feet  wide,  consists  of  gray  hornblende-andesite 
(1568)  crowded  with  minute  phenocrysts,  some  of  the  hornblendes  being 
pi'ominent.  The  rock  is  dense,  and  is  black  and  glassy  near  the  contact  wall 
(1567).  It  cracks  into  small  prisms.  The  groundmass  of  the  center  of  the 
dike  is  hyalopilitic,  and  at  the  margin  is  a  beautiful  brown  glass  with  abun- 
dant microlites  of  feldspar,  pyroxene,  and  magnetite.  The  phenocrysts  are 
labradorite,  greenish-brown  hornblende,  hypersthene,  and  less  augite,  with 
magnetite. 

Another  dike,  with  the  same  northwest  trend,  consists  of  several  vertical 
sheets,  from  2  or  3  to  4  or  5  feet  thick,  inclosing  wedges  of  breccia.  It  is 
dark  bluish  gray,  compact,  without  phenocrysts  (1569),  and  proves  to  be  a 
basalt  rich  in  olivine.  It  exhibits  fine  prismatic  cracking  in  curved  columns 
perpendicular  to  the  walls  of  the  dike,  and  is  in  part  thinl}'  fissile  parallel 
to  the  walls,  and  in  places  is  fissile  across  the  columns.  The  rock  is  dense  and 
glassy  near  the  contact,  and  consists  of  an  aggregate  of  prismatic  feldspar 
microlites  and  more  abundant  grains  of  augite  and  magnetite,  with  almost 
microscopic  phenocrysts  of  serpentinized  olivine. 

Some  distance  south  of  the  dikes  just  noted  is  a  dike  of  dense  g'ray 
rock  without  megascopic  phenocrysts  (1570,  1571).  It  is  a  hornblende- 
pyroxene-andesite,  and  is  glassy  and  black  near  the  contact  face.  The  dike 
is  from  10  inches  to  3  feet  wide  and  trends  northwest.     The  groundmass  of 


314  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  central  part  is  pilotaxitic,  with  some  tabular  microlites  of  feldspar.  At 
the  margin  it  is  brown  glass,  with  prismatic  microlites  of  feldspar.  The 
minute  phenocrysts  are  hyjiersthene  and  augite,  and  there  are  very  few 
of  hornblende. 

Another  parallel  dike,  about  25  feet  wide,  consists  of  hornblende- 
andesite  (1572)  with  small  hornblendes  and  still  smaller  feldspars.  The 
rock  is  porous  and  fissile.  The  groundmass  is  pilotaxitic,  with  tabular  feld- 
spars and  microcryptocrystalline  portions. 

The  next  dike  south  is  parallel  to  the  last  and  has  a  hade  of  75°  SW 
It  consists  of  compact  dark-gray  hornblende-andesite,  with  many  large, 
phenocrysts  of  hornblende.  There  are  some  small  vesicular  cavities  (1573). 
The  groundmass  consists  of  prisms  of  labradorite  with  interstitial  material 
that  is  nearly  isotropic,  is  somewhat  globulitic,  and  contains  magnetite, 
minute  augite,  and  considerable  serpentine,  which  colors  the  whole  rock. 
The  phenocrysts  are  brown  hornblende,  labradorite,  and  a  little  augite. 
It  is  probable  that  the  serpentine  has  been  derived  from  hypersthene. 

The  most  southerly  dike  has  a  general  northwest  trend,  is  about  5  feet 
wide,  and  consists  of  compact  hornblende-andesite  with  small  scattered 
phenocrysts  of  feldspar  and  hornblende.  The  rock  is  dark  purplish  to  red- 
dish, and  has  weathered  to  green,  crumbling,  rounded  masses,  leaving  a 
"slide"  between  indurated  breccia  walls  (1574).  The  groundmass  is  jjilo- 
taxitic,  with  much  reddish-brown  iron  oxide.  The  rocks  of  these  dikes  are 
all  andesitic  in  habit,  and  are  for  the  most  part  glassy  in  thin  section;  some 
are  holocrystalline.  They  are  probably  not  as  deeply  seated  intrusions  as 
those  at  Sylvan  Pass. 

MASSIVE  FLOWS  AND  INTRUSIONS   OF   LIGHT-COLORED    ANDESITE. 

There  are  several  bodies  of  massive  andesite  whose  mode  of  occurrence 
has  not  been  fully  discovered.  They  occur  at  the  present  for  the  most  part 
at  the  summits  of  jjeaks,  and  give  evidence  of  having  been  sui-ficial  flows 
that  occupied  drainage  channels  on  the  ancient  surface  of  the  country.  But 
in  several  instances  they  appear  to  have  been  intrusive  bodies,  since  they 
are  accompanied  by  branching  offshoots  or  apophyses.  The  porous  or 
vesicular  nature  of  the  andesite  composing  these  bodies  makes  it  evident 
that  they  must  have  consolidated  under  little  pressure,  and  that  if  they 


ANDESITE  OF  MOUNT  DOANE.  315 

were  intrusive  bodies  tlie}'  had  reached  very  eJt)se  to  the  surface  of  tlie 
breccias. 

Two  of  the  most  conspicuous  bodies  of  massive  andesite  form  the 
conical  summits  of  Mount  Doane  and  Mount  Stevenson,  and  constitute  the 
ixpper  500  to  900  feet  of  these  mountains.  The  mass  at  Mount  Doane  con- 
sists of  light-gray  compact  hornblende-mica-andesite,  filled  with  minute 
crystals  of  feldspar,  hornblende,  and  biotite,  with  a  few  larger  phenocrysts 
(1575,  1576).  Near  the  bottom  contact  it  is  dark  colored  and  Aveathers 
into  small  rounded  masses.  Higher  up  in  the  body  it  is  columnar,  passing 
into  platy  parting,  in  more  or  less  vertical  slabs. 

The  groundmass  of  the  rock  from  near  the  bottom  contact  is  micro- 
crystalline  and  microlitic,  and  is  gray  in  thin  section.  The  phenocrysts 
are  greenish-brown  hornblende  and  brown  biotite,  both  without  black 
borders  or  any  noticeable  inclusions  of  magnetite.  Magnetite  also  forms 
small  phenocrysts,  the  size  of  the  small  ones  of  hornblende  and  biotite.  It 
is  abundant  as  minute  crystals  in  the  gi-oundmass.  The  labradorite  is  cen- 
trally and  also  zonally  altered  to  a  brown  substance,  jjrobably  kaolin.  In 
the  rock  from  the  summit  of  the  mountain  the  groundmass  is  slightly  more 
coarsely  crystallized,  and  the  structure  is  almost  microgranular,  the  grains 
being  about  0.015  mm.  in  diameter.  The  phenocrysts  are  the  same  as  in 
the  finer-grained  varieties,  but  the  hornblendes  and  biotites  are  filled  with 
minute  grains  of  magnetite,  some  of  the  smaller  hornblendes  being  almost 
completely  replaced  by  it,  and  also  by  some  pyroxene.  Magnetite  forms 
small  phenocrysts,  and  there  are  a  few  of  augite.  The  labradorite  is  almost 
fresh.  A  cross  section  of  the  whole  body  is  shown  in  the  almost  vertical 
cliff"  at  the  northern  face  of  the  mountain.  The  massive  andesite  is  seen  to 
be  resting  on  almost  horizontal  layers  of  hght-colored  breccia,  the  plane  of 
the  bottom  contact  being  curved,  and  rising  several  hundred  feet  at  the  east 
and  west  ends  of  the  section.  The  andesite  body  appears  to  have  been  a 
surficial  flow  which  filled  an  ancient  drainage  channel. 

The  same  appears  to  be  true  of  the  massive  hornblende-mica-andesite 
forming  the  top  of  Mount  Stevenson  (1577  to  1581).  This  rock  is  light 
gray,  with  more  prominent  hornblende  than  in  the  mass  of  Mount  Doane, 
and  contains  segregations  of  hornblende  and  feldspar,  with  a  little  biotite. 
The  groundmass  of  the  light-gray  rock  is  holocrystalline,  with  a  mixture  of 
feldspar  prisms  and  grains,  besides  magnetite  and  pyroxene  grains.     The 


316  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

hornblendes  are  surrounded,  and  in  part  replaced,  by  pyroxene  and  magnet- 
ite. Biotite  is  scarce.  The  labradorite  phenocrysts  contain  some  calcite, 
and  there  is  a  considerable  amount  of  zeolite  scattered  through  the  rock, 
which  is  probably  heulandite  or  raordenite,  which  are  very  much  alike 
optically.  Another  mineral  associated  with  them  is  in  fan-like  aggregates 
of  less  refractive  crystals,  and  is  probably  tridymite.  There  is  also  consid- 
erable calcite.  Where  the  rock  is  darker,  probably  near  a  contact  plane 
(1577),  the  groundmass  is  pilotaxitic  and  the  hornblendes  are  free  from 
magnetite  borders.  The  coarsely  crystallized  segregations  consist  of  lai-ge 
idiomorphic  labradorite  and  hornblende  crystals,  with  some  smaller  ones, 
and  skeleton  forms  of  labradorite  and  some  globulitic  glass  base  in  places. 
There  are  comparatively  large  crystals  of  magnetite  and  apatite  and  consid- 
erable zeolite.  Occasional  large  crystals  of  biotite  occur.  It  appears  to 
reach  a  lower  altitude  on  the  west  side  of  the  mountain.  Beneath  it  thei'e  is 
a  layer  of  rounded  and  waterworn  pebbles  of  andesite.  This  would  also 
appear  to  have  occupied  the  valley  of  an  ancient  channel,  and  may  have 
been  continuous  with  the  mass  of  Mount  Doaue. 

Another  large  body  of  hornblende-mica-andesite  forms  the  upper  por- 
tion of  the  high  northwest  spur  of  Mount  Schurz.  This  body  is  well  exposed 
and  was  studied  on  its  northwestern  and  northeastern  sides.  It  rests  on 
nearly  horizontal  layers  of  light-colored  breccia,  but  its  relations  to  the  dark- 
colored  breccia  were,  not  determined.  A  fine  section  across  the  body  is 
exposed  on  its  northeastern  side.  It  is  beautifully  columnar,  the  columns 
standing  in  various  directions.  The  arrangement  of  the  columns,  as  well  as 
the  slope  of  the  bottom  contact  with  the  underlying  breccia,  which  is 
from  both  sides  inwards,  indicates  that  the  andesite  occupied  a  broad  channel 
sloping  toward  the  southwest,  since  the  western  end  of  the  andesitic  mass  is 
lower  than  the  eastern.  The  altitude  of  the  body  ranges  from  10,000  to 
10,600  feet.  The  columnar  structure  is  very  well  developed  in  curved 
gi'oups,  some  of  the  columns  being  40  feet  long  and  1  foot  in  diameter.  In 
o-eneral  the  columns  start  perpendicular  to  the  surface  of  contact  with  the 
breccia.  Those  in  the  lower  part  of  the  mass  are  larger  than  those  in  the 
iipper  portion. 

The  rock  is  darker  colored  near  its  contact  with  undei'lying  breccia, 
and  is  dense  (1582  to  1584),  but  becomes  lighter  colored  and  more  crys- 
talline farther  from  the  contact.     It  is  more  or  less  vesicular  or  porous, 


ANDESITI-:  OF  MOUNT  SCIITJKZ.  317 

and  is  parted  into  plates  parallel  to  the  plane  of  contact  and  also  into 
colnnnis  perpendicular  to  the  same.  I'he  niegascopical  habit  varies  consid- 
erabl\-  in  diflierent  parts  of  the  l)od\'.  Fifty  feet  from  the  northwestern  lower 
contact  the  rock  is  full  of  prominent  phenocrysts  of  feldspar,  with  smaller 
biotites  and  hornblendes  (1585).  At  75  feet  it  has  less  prominent  feldspars 
and  more  noticeable  hornblende  and  mica  (1586).  In  the  central  part  of 
the  body  it  is  still  lighter  colored,  nnd  compact,  with  the  same  variability  of 
phenocrysts  (1587,  1588).  In  the  cavities  of  some  of  the  porous  forms  there 
are  good  crystals  of  tridymite  (1585,  1589). 

At  the  higher  parts  of  the  body  the  rock  is  darker  colored  again 
(1590,  1591).  Among  the  fragments  lying  at  its  northwestern  base  are 
large  masses  and  columns  of  various  modifications  of  the  rock.  One 
column,  8  feet  long,  is  a  dark-colored,  finely  vesicular  variety  (1592), 
without  prominent  phenocrysts.  Another  variety  is  still  more  vesicular, 
with  light -blue  coating  to  the  vesicles.  It  is  basaltic  in  appearance,  with 
noticeable  feldspars  (1596).  Others  are  dark  and  basaltic  looking,  but  more 
compact,  with  prominent  feldspars  (1594,  1595).  They  all  belong  to  the 
large  andesitic  body. 

The  light-colored  rock  which  constitutes  the  main  mass  of  this  body 
has  a  groundmass  that  is  microcrystalline  and  microlitic.  'It  is  very  much 
like  that  of  the  rock  forming  the  summit  of  Mount  Stevenson.  It  contains 
much  tridymite  in  clusters  of  minute  crystals  and  in  groups  of  twinned 
plates.  The  abundant  small  phenocrysts  are  labradorite,  brown  hornblende 
with  magnetite  and  pyroxene  border,  brown  biotite  with  magnetite  border, 
and  some  augite.  There  is  a  small  amount  of  serpentinized  mineral,  which 
was  probably  hypersthene.  In  the  rock  from  within  75  to  50  feet  of  the 
margin  of  the  body  the  groundmass  is  microlitic  and  possibly  glassy.  The 
phenocrysts  of  hornblende  and  biotite  have  only  a  very  narrow  magnetite 
border  in  the  rock  at  75  feet  from  the  contact  plane,  and  none  at  all  in  that 
at  50  feet  from  the  plane. 

At  the  bottom  contact  the  character  of  the  rock  is  somewhat  changed. 
The  groundmass  is  hyalopilitic,  consisting  of  brown  glass  filled  -with  micro- 
lites.  Phenocrysts  are  fewer,  and  are  labradorite  with  beautiful  glass  inclu- 
sions, hornblende  almost  completely  paramorphosed  to  pyroxene  and 
magnetite,  brown  biotite  with  narrow  border  of  magnetite  and  pyroxene, 
many  small  ^ihenocrysts   of  augite,  and  many  others  that  are  serpentine 


318     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

pseudomorphs  and  have  the  outline  of  ohvine  in  some  cases  and  of  hyper- 
sthene  in  others.  In  one  rock  section  the  serpentine  is  replaced  by  calcite. 
This  appears  to  be  a  more  basic  facies  of  the  main  rock. 

The  dark-colored,  vesicular,  and  basaltic-looking  modifications  of  the 
rock,  already  mentioned  as  lying  at  the  base  of  the  north  slope  of  the 
spur,  resemble  the  rock  from  near  the  bottom  contact  in  the  nature  of  the 
phenocrysts,  which  are  more  abundant  in  these  rocks.  But  the  groundmass 
is  highly  glassy,  and  is  fine  brown  glass  with  many  microlites  of  feldspar, 
pyroxene,  and  magnetite.  This  is  specially  true  of  the  most  vesicular 
modification.  In  it  are  some  small  phenocrysts  of  colorless  olivine  with 
narrow  border  of  pyroxene,  like  that  surrounding  the  serpentine  pseudo- 
morphs just  described. 

The  occurrences  of  massive  andesite  at  Coulter  Peak  and  in  its  vicinity 
are  most  probably  intrusive  in  two  instances  and  surficial  in  the  others. 
There  are  four  distinct  occurrences,  three  of  which  have  been  investigated. 
The  rock  in  all  three  is  the  same  in  composition  and  habit. 

At  Coulter  Peak  it  forms  the  upper  800  to  1,000  feet  of  the  mountain. 
The  rock  is  light  gray,  without  noticeable  phenocrysts,  and  is  quite  uniform 
throughout.  There  are  a  few  thin  crystals  of  hornblende,  fewer  of  feld- 
spar, and  sporadically  biotite.  It  is  slightly  vesicular,  especially  at  the 
summit  of  the  peak  (1605),  but  in  the  lower  portions  is  dense  and  lithoidal 
(1604);  and  near  the  planes  of  contact  with  the  underlying  breccia  it  is 
dark  colored  and  glassy  (1603,  1606).  The  rock  at  the  summit  consists 
of  square  prisms  of  twinned  labradorite,  averaging  0.15  mm.  in  length, 
besides  shorter  rectangular  crystals  and  less  well-defined  grains  with  a 
brownish  tinge.  These  have  a  slightly  lower  refraction  and  are  probably 
more  alkaline  feldspar,  with  some  minute  pyroxene.  There  is  a  little  mag- 
netite. The  small  scattered  phenocrysts  are  labradorite,  paramorphs  after 
hornblende,  with  some  hornblende  in  the  center  of  the  lai-ger  ones;  occa- 
sionally biotite  with  magnetite  border,  and  more  or  less  completely  serpen- 
tinized  hypersthene.  In  the  lower  part  of  the  rock  mass  the  granular 
feldspars  are  larger,  the  whole  being  slightly  coarser  grained  and  lighter 
colored.  Quartz  is  recognizable  among  the  constituent  minerals.  Pheno- 
crysts are  fewer  and  the  hornblende  is  less  changed. 

At  the  bottom  contact  the  rock  is  beautiful  brown  glass,  with  micro- 
lites of  prismatic  and  tabular  feldspar,  in  part  at  least  labradorite;  delicate 


ANIJKSITK  OF  COULTER  PKAK.  319 

prisms  of  pyroxene,  for  the  most  piirt  liyperstlieiie,  and  little  iiuiyiietite. 
The  few  small  phenocrysts  are  labradorite,  browuish-<»-reen  hornblende  with 
little  or  no  border,  hypersthene,  and  augite.  The  mass  is  distinctly  col- 
umnar, in  groups  standing  at  various  angles  and  sometimes  curved.  Near 
planes  of  contact  the  columns  are  normal  to  the  contact  plane.  On  the 
southeastern  spur  the  massive  andesite  overlies  dark-colored  breccia,  and 
the  surface  of  bottom  contact,  though  cpiite  irregular,  slopes  toward  the 
north.  At  the  northern  end  of  the  mass  the  plane  of  bottom  contact  dips 
steeply  south,  its  trend  being  east  and  west.  On  the  west  spur  of  the 
mountain  a  body  of  similar  massive  rock  caps  breccia,  the  contact  dipping 
north.  The  breccias  beneath  the  body  at  Coulter  Peak  lie  horizontal,  and 
the  indications  point  to  the  massive  andesite  being  a  surficial  flow  in  a 
di'ainage  channel  trending  west. 

A  large  body  of  similar  rock  forms  the  upper  portion  of  the  mountain 
1  h  miles  northwest  of  Coulter  Peak.  It  has  the  same  petrographical  char- 
acters, but  is  denser  and  more  crystalline  in  its  main  mass,  approaching  a 
IDOrphyry  or  felsite  (1596,  1597,  1601,  1602).  Near  its  contact  with  the 
breccia  it  is  dark  colored  and  glassy  (1598),  becoming  lighter  oolored  and 
lithoidal  at  a  distance  of  6  inches  (1599),  and  still  more  so  at  a  distance 
of  10  feet  (1600),  where  it  is  vesicular,  with  tridymite  in  good  crystals. 

The  rock  representing  the  body  of  this  mass  is  similar  to  that  of 
Coulter  Peak  in  general  characters,  but  is  more  highly  crystallized.  It 
consists  of  prisms  of  labradorite  about  as  large  as  in  the  other  rocks,  0.15 
mm.  long,  but  few  in  number.  The  tabular  or  granular  feldspar  is  more 
abundant,  and  much  of  it  is  intergrown  with  quartz  in  micrographic 
and  micropoikilitic  structure,  which  is  shown  in  PI.  XXXVIII,  fig.  4. 
Magnetite  occurs  in  minute  grains,  and  there  is  some  serpentine  or  chlorite. 
The  few  small  phenocrysts  of  hornblende  and  biotite  have  narrow  borders 
of  magnetite  in  some  cases  and  none  in  others.  At  the  contact  with  breccia 
it  is  a  brown  glass,  as  at  Coulter  Peak,  in  this  case  faintly  polarizing,  as 
though  devitrified.  The  beautiful  microlites  are  like  those  in  the  other 
brown  glass  just  described,  except  that  there  is  more  green  hornblende, 
without  dark  border.  At  a  distance  of  6  inches  from  the  contact  the  general 
character  of  the  rock  is  the  same,  but  the  brown  glass  base  is  replaced  by 
a  gray  microcryptocrystalline  aggregate,  which  at  10  feet  distance  is  micro- 
crystalline,  many  of  the  parts  being  idiomorphic  crystals  of  feldspar.     The 


320  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

hornblende  lias  a  narrow  border  of  magnetite  grains.  This  body  of  andesite 
is  columnar  and  has  probably  cut  up  through  the  breccias,  its  plane  of 
contact  on  one  side  trending  southwest  and  dipping  steeply  to  the  southeast. 
It  is  exposed  in  an  easterly  escarpment,  where  the  massive  andesite  can  be 
seen  cutting  irregularly  across  the  layers  of  breccia.  It  is  also  well  exposed 
in  a  southerly  escarpment.  In  the  eastern  escarpment  there  is  an  inclined 
sheet  or  dike  of  similar  rock,  which  cuts  up  through  the  breccia  at  an  angle 
of  about  20°  and  thins  out.  It  ai)iiears  to  be  an  offshoot  from  the  large 
body.  Directly  east  of  this  peak,  on  the  ridge  north  of  Coulter  Peak,  there 
is  another  body  of  massive  andesite  of  the  same  kind  Its  plane  of  contact 
with-  the  underlying  upper  basic  breccia  is  steep  and  trends  toward  the 
northeast.  It  is  also  colunmar  along  its  western  exposure.  Near  it  at  the 
south  end  is  a  small  intruded  seam  or  dike  of  similar  rock,  which  is  wholly 
glassy  (1607,  1608).  It  is  yellowish  brown  near  the  margin  and  dark 
colored  at  the  middle.  It  cracks  into  rounded  lumps  and  has  a  perlitic 
structure  on  a  large  scale.  It  is  a  beautiful  yellow  glass  in  thin  section, 
with  well-defined  microlites  of  prismatic  and  of  less  numerous  tabular  feld- 
spars, delicate  prisms  of  pyroxene,  and  grains  of  magnetite.  The  very 
small  phenocrysts  are  brownish-green  hornblende  without  dark  border, 
hypersthene,  augite,  and  labradorite ;  in  all  respects  like  the  glassy  portions 
of  the  rocks  just  described. 

Massive  andesite  of  the  same  character  occurs  as  inti-usive  bodies  in 
the  valley  of  Mountain  Creek.  The  largest  is  at  the  mouth  of  the  valley 
in  the  base  of  the  mountain  on  the  north  side.  Its  boundary  is  obscured 
by  soil  and  dcjbris.  It  cracks  into  plates  and  is  compact  and  light  gray, 
with  a  few  thin  crystals  of  hornblende  (1609).  The  rock  is  a  fine-grained 
aggi-egation  of  feldspar  crystals,  quite  like  the  more  highly  crystallized 
portion  of  the  rock  of  Coulter  Peak,  except  that  there  are  fewer  prisms  and 
more  in-egularly  shaped  grains.  The  component  minerals  are  the  same, 
and  the  few  small  phenocrysts  of  green  hornblende  and  brown  biotite 
inclose  much  magnetite. 

Several  small  intrusive  bodies  cut  the  breccia  east  of  the  mouth  of  the 
north  fork  of  the  creek.  One  is  a  narrow  vertical  dike.  It  is  light  gray, 
with  a  few  thin  crystals  of  hornblende,  and  is  slightly  vesicular.  It 
becomes  dark  colored  and  glassy  near  the  contact,  and  is  brecciated  in 
places  (1612).     Parts  of  it  are  compact,  reddish  brown  and  mottled,  but 


TEACIIYTIC  RIIYOLITE.  321 

not  (listinctly  breeciatod  (1613).  Microscopically  it  is  the  same  as  the 
rock  of  Coulter  Peak,  tlie  lithoiclal  portion  being-  holocrystalline,  with 
abundant  prismatic  microlites  of  feldspar  that  exhibit  a,  pronounced  fluidal 
arrangement.  The  glassy  portion  consists  of  clear  yellowish-brown  glass, 
with  microlites,  as  in  the  glass  of  the  Coulter  Peak  rock.  The  few  small 
phenocrysts  of  brownish-green  hornblende  have  margins  of  loosely  aggre- 
gated pyroxene  and  magnetite.  The  other  mass  has  the  same  characters. 
It  is  dense,  gray,  and  lithoidal,  and  is  partly  vesicular  with  good  crystals 
of  trid>'mite  (1611,  1610).  It  also  has  the  same  microscopical  characters. 
A  surhcial  flow  of  pyroxene-andesite  occurs  on  the  summit  of  the  ridge 
north  of  ^liddle  Creek,  already  mentioned  in  another  place. 

TRACIIYTIC  RHYOIilTE. 

Closely  connected  with  the  early  acid  breccia  on  Yellowstone  River 
in  the  neighborhood  of  Crescent  Hill  and  Junction  Butte  are  remnants  of 
a  lava  stream  of  light-colored  lithoidal  rock  whose  most  pronounced  miner- 
alogical  feature  is  the  presence  of  abundant  phenocrysts  of  sanidine 
without  any  of  quartz.  It  passes  into  breccia  in  places,  and  appears  to 
have  been  contemporaneous  with  the  earlier  acid  andesitic  breccia  of  the 
region.  Whether  the  scattered  occurrences  of  this  rock  in  the  bottom  of 
one  large  valley  were  originally  connected  and  were  parts  of  one  large 
sheet,  or  whether  they  belong  to  several  eruptions,  is  not  definitely  known. 

Areas  of  this  rock  occur  along  the  south  side  of  Yellowstone  River, 
forming  a  cliff  at  about  6,400  feet  altitude  from  Geode  Creek  around  the 
north  base  of  Crescent  Hill  to  Yanceys.  It  occurs  somewhat  higher  on 
the  north  side  of  the  Yellowstone  River  west  of  Hellroaring  Creek,  lying 
between  6,600  and  7,200  feet  altitude.  It  extends  east  around  the  north 
end  of  Junction  Valley  and  forms  the  base  of  Junction  Butte  east  of  the 
river.  It  occurs  on  the  north  of  Lamar  River  opposite  the  butte,  and  500 
feet  above  the  river,  and  also  near  the  mouth  of  Slough  Creek.  Patches 
of  it  are  found  on  the  end  of  Specimen  Ridge  1,500  feet  above  the  river. 
Lavas  similar  to  this  occur  as  intimately  associated  with  the  basic  andesitic 
breccias  north  of  the  Yellowstone  Park,  on  Buffalo  Plateau  and  on  the 
flanks  of  Sunset  Peak. 

The  rock  is  generally  light  colored,  and  varies  from  white  and  gray  to 
yellow,  buff,  brown,  red  or  pink,  purplish,  and  green.     In  most  places  it  is 

-21 


322  GEOLOGY  OF  THE   YELLOWSTONE  NATIONAL  PARK. 

litlioidal  to  earthy;  also  compact  and  deuse.  lu  one  locality  it  is  glassy 
and  greenisli  gray,  in  part  perlitic,  passing  into  dark-gray  and  black  glass, 
and  constituting  a  pitchstone  (683,  684).  In  nearly  every  instance  it  is 
mottled  with  Avhat  appear  to  be  inclosed  fragments  having  a  different 
character,  and  which  are  mostlv  tuif  of  the  same  rock.  They  are  often 
flattened,  giving  the  rock  a  distinct  flow  structure.  The  phenocrysts  vary 
in  abundance  and  size  in  different  modifications  of  the  rock.  They  are 
sanidine,  plagioclase,  and  biotite.  Sanidine  is  generally  perfectly  fresh  and 
exhibits  a  brilliant  cleavage  surface,  while  the  plagioclase  is  often  decom- 
posed and  is  fresh  in  oidy  a  few  cases.     Biotite  is  subordinate  in  amount. 

In  places  the  rock  carries  many  fragments  of  andesite  and  of  crystalline 
schist,  and  passes  ujjward  into  breccia  filled  with  the  latter,  and  merges  into 
andesitic  breccia  similar  to  that  already  described  as  underlying  it  This 
relation  may  be  observed  at  the  northern  base  of  Crescent  Hill  and  on  the 
ridge  opposite  the  mouth  of  Hellroaring  Creek.  It  was  the  product  of 
eruption  of  an  exceptional  modification  of  magma,  rich  in  sanidine,  which 
occurred  early  in  the  period  of  the  extravasation  of  the  hornblende-mica- 
andesite,  Avhen  crj^stalline  schists  formed  the  surface  of  the  country  through 
which  the  eruptions  took  place. 

This  light-colored  porphyritic  lava  consists  of  an  abundant  groundmass, 
which  is  in  nearly  all  cases  megascopically  lithoidal  and  under  the  micro- 
scope is  highly  varied  in  structure.  In  this  groundmass  are  numerous 
phenocrysts  of  sanidine  and  lime-soda  feldspar,  which  in  numerous  cases  is 
decomposed.  Ferromagnesian  minerals  are  scarce.  The  only  ones  recog- 
nized megascopically  are  small  biotites.  In  thin  sections  of  the  rock 
pyroxene  is  seen,  in  some  cases  in  almost  microscopic  crystals.  A  -very 
little  green  hornblende  occurs  in  a  few  cases.  The  sanidine  crystals  are 
2  mm.  long  and  smaller,  and  are  usually  twinned  according  to  the  Carlsbad 
law.  Their  cross  sections  are  generally  rectangular,  but  they  often  have 
iri'egular  outlines,  as  though  fragments  of  former  well-shaped  crystals.  The 
same  is  also  true  of  plagioclase.  The  sanidines  are  very  free  from  inclusions 
of  foreign  material;  occasional  inclusions  of  glass,  apatite,  and  zircon  occur. 
The  pinacoidal  cleavages  are  often  well  developed,  but  some  crystals  are 
almost  free  from  cleavage  cracks  and  are  easily  mistaken  for  quartz.  The 
lime-soda  feldspar  is  similar  to  sanidine  in  size  and  general  form,  but  exhibits 
polysynthetic  twinning  according  to  albite,  pericline,  and  Carlsbad  laws.     In 


TKAOUYTIC  RHYOLITE.  323 

a  number  of  cases  tlie  synimetrical  extinction  angles  tested  by  Micliel  Levy's 
nu'tli(Kl  indicate  that  the  feldspar  is  labradorite  as  high  in  lime  as  Abo  Ang. 
In  other  rock  sections  tlie  only  syniiuetrical  extinction  angles  are  Ioav,  but 
they  are  few,  and  may  possibly  belong  to  labradorite.  These  feldspars  also 
are  quite  free  from  inclusions.  They  are  more  easily  decomposed  than  sani- 
dine,  and  in  a  luimber  of  rock  sections  are  completely  altered,  while  the 
sanidine  is  fresh.  The  usual  alteration  is  to  a  microcrystalline  aggregate 
with  low  double  refraction,  probably  kaolin.  Occasionally  the  feldspar  is 
replaced  by  calcite.  Biotite  occurs  in  irregularly  outlined  crystals  of  very 
small  size.  It  is  brown  and  has  a  very  small  optic  angle.  Augite,  when 
present,  forms  idioinorphic  and  also  irregularly  shaped  crystals,  apparently 
fragments  of  lai-ger  crystals.  Its  colors  and  general  character  are  the  same 
as  those  of  the  augite  in  the  associated  andesites.  The  same  is  true  of  the 
few  small  fragments  of  green  and  brownish-green  hornblende.  Ilmenite, 
or  titaniferous  magnetite,  is  jweseut  in  comparatively  large  microscopic 
crystals  and  grains.  Its  character  is  indicated  b}'  its  alteration  product 
and  its  form,  since  it  alters  to  a  white  opaque  mineral  crossed  by  lines  in 
three  directions.  It  is  similar  to  the  occurrence  of  titaniferous  iron  oxide 
in  the  rhyolite  of  the  region.  With  it  are  associated  colorless  apatite  and 
zircon.  There  are  a  few  yellow,  almost  isotropic,  pseudomorphs,  possibly 
after  hypersthene. 

The  groundmass  is  in  many  cases  brecciated,  and  is  made  up  of  patches 
with  diiferent  kinds  of  microstructure.  It  also  contains  fragments  of  other 
rocks,  such  as  andesite  and  the  crystalline  schists.  Large  fragments  of  the 
latter  are  found  in  places,  and  the  massive  lava  grades  into  tiiff-breccia  in 
some  localities.  Only  a  small  part  of  the  rock  is  glassy  and  unaltered  (683). 
Numerous  thin  sections  show  that  the  rock  was  once  glassy  in  many  places 
but  has  become  more  or  less  completely  devitrified.  The  glassy  form  con- 
sists of  glass  that  is  globvilitic  and  brown  in  places,  with  streaks  and  lumps 
that  are  colorless,  and  microlitic  and  trichitic,  with  pyroxene  and  magnetite, 
quite  like  some  rhyolitic  glasses.  It  has  eutaxitic  and  flow  structures  and 
is  spherulitic  in  places.  Perlitic  cracking  is  developed  to  some  extent. 
Small  lumps  with  beautiful  brown  glass  full  of  microlites,  and  others  con- 
taining augite  and  hypersthene,  and  holocrystalline  pieces  of  jjyroxeiie- 
andesite  in  this  glassy  lava,  suggest  that  its  eruption  was  subsequent  to  that 
of  pyroxene-andesite,  which  is  the  case  for  similar  trachytic  lava  farther 


324     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

north  on  Bnffalo  Plateau  and  southeast  of  Sunset  Peak.  These  rocks  are 
filso  identical  microscopically  with  this  glassy  modification  of  the  trachytic 
lavas  north  of  Crescent  Hill. 

Other  parts  of  the  rock  are  l3recciated  flows,  with  lumps  that  are 
devitrified  perlitic  glass,  with  raicrogranular  and  microcryptocrj-stalline  por- 
tions. These  retain  the  small  phenocrysts  and  microlites  intact.  Some  are 
composed  of  minute  fragments  of  glass  with  very  irregular  shapes,  welded 
together  as  in  many  rhyolites.  They  are  devitrified  and  microcryptocrys- 
talline.  Some  of  the  groundmasses  are  colored  yellow,  orange,  or  red  by 
clouded  particles  of  hydrous  oxide  of  iron.  Less  often  the  color  is  green, 
from  chloritic  infiltration. 

The  grouudmass  is  wholly  devitrified  in  many  cases  where  the  feldspar 
phenocrysts  are  still  fresh.  In  a  number  of  instances  the  rock  is  wholly 
altered,  both  kinds  of  feldspar  having  been  reduced  to  kaolin,  and  the  other 
phenocrj'sts  being  decomposed  and  the  groundmass  reduced  to  a  micro- 
crystalline  to  microcryptocrystalline  aggregation.  One  modification  of  the 
rock  is  somewhat  andesitic,  all  of  the  feldspar  phenocrysts  being  lime-soda 
feldspar  (709). 

The  chemical  composition  of  the  rock  is  shown  by  analysis  1.  It 
is  of  a  variety  (679)  which  has  fresh  phenocrysts  of  sanidine  in  abundance 
and  fresh  labradorite  and  a  little  biotite.  The  groundmass  is  devitrified,  and 
there  is  some  chlorite.  The  loss  upon  ignition  is  high  and  indicates  partial 
alteration.  If  anhydi-ous  the  silica  would  be  66  per  cent,  and  the  rock 
would  be  about  on  the  dividing  line  between  (piartz -soda- trachyte  or  highly 
siliceous  soda-trachyte  and  rhyolite.  The  presence  of  labradorite  in  a  rock 
with  so  little  lime  and  so  much  soda  is  surprising,  and  it  is  evident  that  the 
orthoclases  must  be  rich  in  soda.  The  chemical  composition  of  the  very  similar 
rock  near  Sunset  Peak  on  Bear  Gidch,  mapped  in  the  Livingston  folio 
(No.  1)  of  the  Geologic  Atlas,  is  shoAvn  in  the  accompanying  analysis  2. 
It  is  higher  in  silica  and  in  allvalies,  the  potash  being  exceptionally  high  for 
rocks  of  this  region.  This  rock  is  chemically  trachj'tic  rhyolite.  Mineral- 
ogically  all  of  these  rocks  are  characterized  by  the  absence  of  quartz  as 
phenocrysts.  The  groundmass  is  highly  siliceous,  and  quartz  is  present  in 
the  microcrystalline  modifications. 


TKACUYTIG  KHYOLITE. 


325 


Analyses  of  trachytic  rhyolite. 

[Analysts:  1,  J.  E.  Whitflcld;  2,  L.  G.  Eakins.] 


Coii.stitut'nt. 

1. 

2. 

SiO- 

64.65 

Trace. 

17.80 

2.33 

2.10 

Trace. 

69.45 

.19 

14.92 

3.16 

.23 

.07 

.03 

1.19 

.05 

TiO. 

Al  0, 

Fe.Oi 

FeO 

MuO 

BaO 

CaO 

1.73 
.81 
.17 

4.18 

2.83 

Trace. 

.43 

3.06 

MgO •- 

Li,0 

NaO 

3.19 

5.95 

.06 

K  .0 

P,0^ 

SO, 

H,0 

1.69 

■  100.  09 

100. 18 

Trachytic  tuffs  similar  in  composition  occur  in  two  other  locahties  in  the 
Park.  One  is  on  the  south  fork  of  Beaverdam  Creek,  where  it  overHes 
shoshonite,  and  the  other  is  at  Two  Ocean  Pass,  where  it  occurs  in  the 
bottom  of  the  andesitic  breccia  near  the  basaltic  lavas  (shoshonite).  They 
are  all  alike  in  being  composed  of  a  glass;,'  groundmass,  with  phenocrysts 
of  sanidine  and  lime-soda  feldspar,  besides  biotite,  magnetite,  or  ilmenite 
and  many  inclusions  of  other  rocks,  pyroxene-andesites  for  the  most  part 
(1650,  1722,  and  1725).  In  the  rock  from  Two  Ocean  Pass  there  are 
labradorite  crystals  and  fragments  and  numerous  broken  augites,  as  well  as 
pieces  of  andesite.  In  this  rock  it  is  possible  that  the  labradorite  crystals 
may  have  been  derived  from  the  andesite  dust.  The  presence  of  labradorite 
in  association  with  orthoclase  in  parts  of  this  rock  corresponds  to  the  simi- 
lar association  of  these  two  feldspars  in  shoshonite  and  banakite,  and  indi- 
cates a  genetic  relationship,  which  is  also  indicated  by  the  close  association 
of  these  rocks  in  the  field. 


CHAPTER    IX. 

absarokite-shoshonitp:-banakite  series. 


By  Joseph  Paxson  Iddings. 


INTRODUCTIOIS^. 

There  are  certain  basaltic-looking  rocks  associated  with  the  older 
andesitic  breccias  in  various  localities  within  the  Park,  which  form  lava 
flows  in  most  cases  and  dikes  in  others,  and  which  more  rarely  constitute 
part  of  the  basic  breccia  itself.  They  are  usually  quite  subordinate  in 
amount,  judging  from  the  extent  of  their  exposures,  but,  considering  the 
probable  size  of  their  original  masses,  before  being  exposed  by  erosion 
thev  must  have  had  very  considerable  volumes.  As  flows  they  are  basaltic 
in  character,  being  dark  colored  and  heavy,  with  olivine  among  the  pheno- 
crysts  in  most  cases.  They  are  massive  and  compact  or  vesicular.  They 
are  jjorphyritic  in  some  cases,  but  not  noticeably  so  in  others,  and  generally 
exhibit  a  semiwaxy  luster  that  suggests  the  presence  of  nepheline,  which, 
lio^ever,  is  not  present.  The  waxy  luster  is  due  to  the  alkali  feldspar  in 
the  groundmass.  They  are  often  dull  greenish  black  owing  to  the  serpen- 
tinization  of  olivine.  As  dikes  they  are  basaltic  in  some  cases  and  trachytic 
in  others,  l^eing  gray  in  vaiious  shades,  and  having  a  somewhat  waxy  luster 
in  the  rocks  of  darker  shades.  The  luster,  as  in  the  case  of  the  flows,  is 
due  to  the  alkali  feldspars,  as  there  is  no  uepheline.  They  are  porphyritic 
or  not  in  diff"erent  cases,  and  range  from  aphanitic  to  phanerocrystalline. 
As  will  be  seen  later,  they  represent  a  rather  wide  range  of  composition, 
both  chemical  and  mineralogical,  and  though  genetically  related  and  con- 
nected by  gradual  transitions,  so  that  they  constitute  a  natural  group,  they 
could  not  be  embraced  by  any  one  definition  and  must  be  divided  into 
several  classes. 

326 


ABSAUOKITE  AND  SHOSifONITE.  327 

The  cliiot"  chnractevistics  of  the  most  basic  class  are  the  presence  of 
abuiidant  phenocrvsts  of  olivine  and  angite  and  the  absence  of  any  of  feld- 
spar. The  groundniass  may  be  anything-  from  a  dark  glass  to  an  almost 
phanerocrystalline  light-gray  mass.  It  is  oftener  aphanitic  and  dark 
greenish  gray.  The  phenocrysts  are  large  and  pronounced  in  many  cases, 
but  are  very  small  in  othei's.  The  microscopical  characteristics  will  be 
given  at  length.  Chemically  they  are  low  in  silica,  from  46  to  52  per  cent; 
low  in  alumina,  from  'J  to  12  per  cent;  high  in  magnesia,  from  8  to  13  per 
cent;  comparatively  high  in  alkalies,  with  potash  considerably  higher  than 
soda,  except  in  one  case.  The  molecular  ratio  of  the  alkalies  to  silica  is 
0.08  and  0.09.  After  the  crystallization  of  abundant  phenocrysts  of  olivine 
and  augite  the  remainder  of  the  magma,  owing  to  the  low  alumina  and  to 
relatively  high  alkalies,  was  so  constituted  that  alkali-feldspathic  minerals, 
in  the  form  of  orthoclase  or  leucite,  might  crystallize  out,  which  they  did 
or  not  according  to  the  conditions  under  which  solidification  took  jjlace. 

The  principal  characteristic  of  the  second  class  is  the  presence  of 
phenocrysts  of  labradorite,  together  with  those  of  augite  and  olivine,  in  a 
gi'oundmass  that  is  usually  dark  greenish  gi'ay,  with  a  semiwaxy  luster, 
but  which  may  be  glassy  or  phanerocrystalline,  and  which  when  distinctly 
crystallized  contains  a  notable  percentage  of  orthoclase.  They  range  from 
varieties  rich  in  olivine  and  augite,  which,  with  decreasing  labradorite, 
grade  into  rocks  of  the  first  class,  to  varieties  with  few  olivines  or  augites. 

Chemically  they  contain  from  50  to  56  per  cent  of  silica.  Alumina  is 
moderate  to  high,  from  17  to  19.7  per  cent.  Lime  and  magnesia  are  moderate 
to  low,  the  former  from  8  to  4.3  per  cent,  the  latter  from  4.4  to  2.5.  The 
alkilies  are  moderately  high,  with  potash  comparatively  high  for  rocks  of 
this  region,  with  like  amounts  of  silica,  from  3.4  to  4.4  per  cent,  the  soda 
ranging  from  3  to  3.9  per  cent.  The  molecular  ratios  of  the  alkalies  to 
silica  is  0.10  and  0.1 1 .  After  the  crystallization  of  phenocrysts  of  labradorite, 
olivine,  and  augite,  the  remainder  of  the  magma  was  rich  in  alkali-feld- 
spathic material,  usually  that  of  orthoclase,  which  shows  itself  in  the  ground- 
mass  according  to  conditions  of  crystallization. 

Rocks  corresponding  chemically  to  both  of  these  classes  occur  with  no 
megascopic  phenocrysts,  and  in  various  phases  of  crystallization,  from 
glassy  to  holocrystalline,  and  almost  phanerocrystalline ;  consequently  they 
differ  from  them  not  only  in  microstructure  but  in  the  minerals  that  have 


328     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

been  developed.  They  occur  both  as  lava  flows  and  as  dikes,  but  no  special 
characteristics  can  be  connected  with  either  mode  of  occurrence,  except 
that  the  more  highly  crystallized  forms  are  found  as  dikes.  Not  all  the 
dikes,  however,  are  more  crystalline  than  all  the  lava  flows. 

Rocks  of  the  third  class  are  known  mostly  in  the  form  of  dikes,  and 
in  only  a  few  localities.  The  rocks  are  highly  feldspathic,  with  small 
amovmt  of  ferromagnesian  minerals,  and  these  chiefly  biotite  with  sub- 
ordinate augite.  The  ])henocrysts  are  labradorite  in  a  groundmass  rich  in 
orthoclase.  Chemically  they  have  51  to  61  per  cent  of  silica,  16.7  to  19.6 
per  cent  of  alumina,  3.5  to  6  per  cent  of  lime,  1  to  4  per  cent  of  magnesia, 
3.8  to  4.5  per  cent  of  soda,  and  4.4  to  5.7  per  cent  of  potash.  The  ratio  of 
alkalies  to  silica  is  0.13  and  0.14.  Since  much  of  the  calcium  and  sodium 
goes  into  the  phenocrysts  of  labradorite,  the  feldspathic  groundmass  is  rich 
in  potash  and  is  largely  orthoclase.  The  rocks  stand  at  the  end  of  the 
series,  representing  the  variation  reached  when  all  the  phenocrysts  are 
labadorite  and  when  biotite  occurs  instead  of  olivine  and  augite. 

The  division  of  the  series  into  three  parts  is  wholly  artificial  and  for 
convenience.  There  is  gradation  from  one  end  to  the  other,  and  from  the 
middle  of  the  series  into  the  normal  basaltic  rocks  of  the  region,  which  will 
be  pointed  out  later.  Tlie  three  classes  will  be  described  under  the  names 
absarokite,  shoshonite,  and  banakite. 

ABSAROKITE. 

All  of  the  rocks  here  classed  as  absarokites  carry  abundant  phenocrysts 
of  olivine  and  augite,  except  two  (1282  and  1624).  These  are  classed  with 
them  on  the  ground  of  chemical  identity.  The  rocks  occur  in  the  Absaroka 
Range,  and  also  in  other  parts  of  the  Yellowstone  Park,  being  found  upon 
Mirror  Plateau  (1151,  1152),  within  the  region  of  the  Crandall  volcano  (1282, 
1277,  1306,  1307),  at  Signal  Point,  Yellowstone  Lake  (1617,  1618),  at 
Two  Ocean  Pass  (1719,  1720),  on  Coulter  Creek  (1743),  about  the  head- 
waters of  Conant  Creek  (1745, 1751),  and  in  the  Ishawooa  Canyon  (1698). 
The  absarokite  is  found  as  bowlders  on  the  west  shore  of  Yellowstone  Lake, 
south  of  Bridge  Bay,  probably  coming  from  Signal  Point,  on  the  east 
shore. 


CHEMICAL  COMPOSITION  OF  ABSAROKITE. 


329 


Tlio  chemicfil  composition  of  six  of  these  rocks  is  shown  l)y  the  follow- 
ing  auulvses,    the    characteristic   features   of    which  have   already   been 

indicated : 

Analyses  of  absaroMtes. 


Constituent. 

1 

2 

3 

4 

5 

6 

SiOj     

48.28 

.88 

11.56 

3.52 

5.71 

.13 

48.95 

.49 

12.98 

3.63 

4.68 

.13 

48.36 

1.18 

12.42 

5.25 

2.48 

.13 

.29 

9.36 

8.65 

1.46 

3.97 

.84 

Trace. 

51.76 

.47 

.12.36 

4.88 

4.60 

.11 

49.71 

1.57 

13.30 

4.41 

3.37 

.17 

.46 

7.96 

8.03 

1.49 

4.81 

.66 

Trace. 

51.68 

1.08 

14.07 

4.71 

4.57 

Trace. 

TiO. 

Al.On 

KeO, 

FeO 

MuO 

B-iO 

MgO 

13.17 

9.20 

2.73-2.89 

2. 17-2. 22 

.59 

11.73 

7.66 

2.31 

3.96 

.67 

9.57 
7.14 
1.99 
3.83 
.56 

7.72 

6.65 

2.45 

4.16 

.72 

SO3 .  13 

LijO  Trace. 

2.09 

CaO          

Na:0 

K.O          

PiOs 

Cr  O 

CI 

.18 
2.96 

HjO 

3.16 

5.54 

3.05 

4.07 

Total 

Less  0  for  CI 

100. 08 
.04 

100.  35 

99.93 

100.  32 

100.  01 

100. 03 

100.04 

1.  Leiicite-absarokite,  Ishawooa  Canyon,  Wyoming.     Analyst,  J.  E.  Whitfield.     (1698.) 

2.  Absarokite,  dike  at  liead  of  Lamar  River.     Analyst,  L.  G.  Eakius.     (1306.) 

3.  Absarokite,  dike  south  of  Clark  Fork  River.     Analyst,  L.  G.  Eakins.     (1277.) 

4.  Absarokite,  lava  flow,  head  of  Raven  Creek.     Analyst,  L.  G.  Eakins.     (1151.) 

5.  Absarokite,  dike,  divide  east  of  Cache  Creek.     Analyst,  L.  G.  Eakins.     (1282.) 

6.  Absarokite,  lava  flow.  Two  Ocean  Pass.     Analyst,  J.  E.  Whitfield.     (1720.) 

The  six  analyses  are  arranged  according  to  decreasing  percentage  of 
magnesia.  The  first  two  have  the  highest;  the  second  two,  over  9  per  cent; 
the  fifth  and  sixth  have  7.96  and  7.72,  which  are  not  very  high  for  a  rock 
so  low  in  silica.  There  is  an  increasing  range  in  alumina  and  in  potash. 
The  second,  third,  and  fourth  analyses  are  closely  alike.  The  first  and  last 
two  are  not  so  much  alike  that  they  might  not  be  considered  separately. 
The  chief  dijfferences  are  in  the  magnesia  and  alkalies,  but  they  are  related 
in  other  respects.  They  all  exhibit  considerable  loss  upon  ignition,  corre- 
sponding to  the  amount  of  hydration  due  to  alteration  or  to  the  presence  of 
zeolitic  minerals. 

As  already  said,  the  rocks  here  grouped  together  diifer  somewhat  in 


330  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  mineral  composition  of  the  groundmass  as  well  as  in  its  microstructure. 
The  rock  with  the  largest  grain  and  most  highly  developed  crystallization 
is  that  whose  chemical  composition  is  given  in  the  first  analysis  (1698).     It 
was  not  found  in  place,  but  was  collected  from  a  bowlder  3  or  4  miles  from 
the  junction  of  the  streams  in  Ishawooa  Canyon.     It  is  nearly  holocrystal- 
line,  and  was  probably  an  intrusive  rock  in  the  form  of  a  dike.     It  consists 
of  abundant  phenocrysts  of  olivine  and  augite,  about  3  mm.  in  diameter  and 
smaller,  and  of  a  subordinate  amount  of  gray  crystalline  "groundmass.     In 
thin  section  the  olivine  is  colorless  and  very  free  from  inclusions,  with 
almost  no  serpentinization.     The  augite  is  pale  green,  with  high  extinction 
angle,  reaching  42°..    It  incloses  some  olivine  and  magnetite.     The  form 
of  these  phenocrysts  is  only  partially  idiomorphic,  the  outline  being  quite 
jagged  in  some  cases,  and  the  reentrant  angles  being  occupied  by  orthoclase, 
as  though  the  crystallization  of  the  olivine  and  augite  had  continued  into 
the  period  in  which  the  felds]3ars  of  the  groundmass  were  forming.     There 
was  no  hiatus  between  the  crystallization  of  the  phenocrysts  and  that  of  the 
o'roundmass.      The  two  were  connected  and  continuous.     The  groundmass 
consists  of  crystals  of  orthoclase  and  leucite,  which  are  nearly  idiomorphic, 
although  the  mass  is  holocrystalline,  except  for  occasional  possible  remnants 
of  glass  base,  wliich  form  angular  patches  between  the  crystals.     There  are 
also  small  irregularly  shaped  crystals  of  augite  and  olivine,  with  magnetite 
and  much  apatite  in  long  slender  needles.     The  orthoclase  and  leucite  are 
not  uniformly  mingled,  but  are  clustered  in  groups.     The  orthoclase  is  in 
rectangular  prisms,  twinned  according  to  the  Carlsbad  law,  and  about  0.4 
mm.  long  and  smaller.     Very  rarely  they  contain  minute  cores  of  lime- 
soda  feldspar,  with  symmetrical  extinction  angles  of  30°,  corres]Donding  to 
labradorite.     The  substance  of  the  feldspar  is  very  fresh  and  unaltered. 
The  leucite  is  partly  idiomoi-phic,  partly  allotriomorphic,  and  in  some  cases 
exhibits  the   characteristic    double    refraction,   though    most    crystals    are 
isotropic.     Central  aggregations  of  minute  augite  grains  occur.     In  places 
a  cloudy  alteration  has  set  in,  resulting  in  a  zeolitic  mineral  whose  exact 
nature  has  not  been  determined.     Owing  to  the  small  amount  of  material 
collected,  no  separations  or  partial  analyses  were  attempted.     The  determi- 
nation (if  the  alkalies  was  repeated  and  found  to  accord  closely  with  the 
first  determination. 

The  needles  of  apatite  are  very  delicate  and  traverse  the  feldspathic 


ABSAHOKITE.  331 

crystals  of  the  groumlinass  in  all  directions,  but  do  not  ])enetrate  tlie  jilieno- 
crysts  of  olivine  and  aug'ite,  indicating-  tliat  tlie  formation  of  the  a})atite  was 
not  anionji'  the  earliest  of  the  crystaHizations,  but  took  place  when  the 
groundmass  crystallized.' 

The  development  of  orthoclase  and  leucite  from  a  magma  so  low  in 
alkalies  and  with  so  little  potash  is  notable.  The  almost  total  absence  of 
lime-soda  feldspar  is  plainly  due  to  the  low  percentage  of  alumina,  which 
was  nearly  all  combined  Avitli  the  alkalies  to  form  alkali-feldspathic  min- 
erals. It  is  evident  that  both  the  orthoclase  and  leucite  must  be  rich  in 
soda.  The  formation  of  leucite  was  undoubtedly  controlled  by  the  low 
percentage  of  silica,  which  if  higher  would  have  formed  a  polysilicate  of 
all  the  aluminum  and  alkahes,  instead  of  a  metasilicate  and  polysilicate. 
The  earliest  compovinds  to  crystallize — olivine  and  augite — consumed  the 
magnesia  and  lime,  with  iron  oxide  and  some  alumina,  and  possibly  some 
soda.  It  is  evident  that  the  remaining  magma  contained  lime  in  sufficient 
amount  to  satisfy  the  phosphoric  oxide,  besides  a  little  that  combined  with 
alumina  and  silica  to  form  labradorite.  Moreover,  the  alkalies  and  alumina 
were  left  in  the  proper  proportions  to  form  alkali-feldspathic  minerals.  In 
a  molten  condition  they  did  not  exist  as  molecules  of  these  minerals,  yet 
we  see  the  indication  of  an  influence  that  controlled  the  proportions  of  the 
partially  dissociated  elements.  At  the  time  of  the  crystallization  of  the 
alkali-feldspathic  constituents  there  were  small  amounts  of  ferromagnesian 
silicates  still  liquid,  which  crystallized  at  this  time. 

The  rock  most  closely  related  to  the  one  just  described  in  chemical 
composition  occurs  as  a  dike,  4  feet  wide,  on  the  divide  between  Lamar 
River  and  Crandall  Creek,  south  of  Hoodoo  Mountain.  It  is  dark  colored 
(1306,  1307)  and  aphanitic,  with  abundant  large  crystals  of  augite  5  to  10 
mm.  in  diameter  and  smaller  phenocrysts  of  olivine.  On  the  sides  of  the 
dike  a  thin  layer  of  the  rock  is  glassy  and  black. 

In  thin  section  the  body  of  the  dike  is  holocrystalline  and  very  line 
grained.  The  groundmass  consists  of  indistinctly  outlined  lath-shaped  feld- 
spars with  low  angles  of  extinction,  besides  an  indistinct  feldspathic  mineral 
as  cement,  which  is  cloudy.  The  lath-shaped  feldspars  appear  to  be,  in  part 
at  least,  orthoclase  with  minute  latli-shaped  cores  of  lime-soda  feldspars. 

'  Arnold  Hague,  Notes  on  the  occurrence  of  a  leucite  rock  in  the  Absaroka  Range,  Wyoming 
Territory:  Am.  Jour.  Sci.,  Sd  series,  Vol.  XXXVIII,  July,  1889,  pp.  43-47. 


332     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Nothing  resembling  leucite  or  suggesting  it  is  present.  This  feldspar  matrix 
is  crowded  with  microscopic  crystals  of  augite,  magnetite,  and  brown  biotite 
in  thin  tablets  and  long  narrow  crystals  which  often  resemble  hornblende. 
In  one  part  of  the  rock  ilmenite  accompanies  magnetite.  The  groundmass 
of  the  edge  of  the  dike  is  brown  glass  with  microlites  of  augite  and  some 
of  plagioclase.  These  microlites  have  dark-browiji  clouds  attached  to  their 
ends,  or  in  the  case  of  augite  are  colored  brown. 

The  augite  phenocrysts  are  light  green  in  thin  section  and  are  filled  with 
irregularly  shaped  inclusions  of  crystalline  g-roundmass  containing  ilmenite 
rods,  which  are  not  generally  found  in  the  grovindmass  of  the  rock  outside 
of  the  augites.  These  ilmenite  rods  within  the  inclusions  of  one  augite  lie 
in  several  orientations,  apparently  with  rhombohedral  symmetry.  Although 
they  are  confined  to  the  inclusions  of  groundmass  and  do  not  penetrate 
the  augite  substance,  their  shape  and  arrangement  suggest  the  microscopic 
rod-like  inclusions  in  the  diallage  and  hypersthene  of  gabbro,  which  may 
possibly  be  ilmenite.  The  augites  also  inclose  small  crystals  of  olivine  and 
magnetite. 

The  olivine  phenocrysts  are  sharply  idiomorphic  and  of  very  pure  sub- 
stance, with  small  inclusions  of  magnetite  and  glass  and  occasionally  bays 
of  groundmass.  It  is  sometimes  twinned  in  pairs  of  attached  crystals,  the 
twinning  plane  being  (Oil).  There  is  a  slight  serpentinization  along 
the  surface  and  cracks  in  some  cases.  The  olivine  crystals  are  much 
smaller  than  those  of  augite,  but  are  more  numerous.  The  appearance  of 
this  rock  in  thin  section  is  shown  in  PI.  XXXVI,  fig.  1. 

It  is  to  be  observed  that  the  glassy  groundmass  of  the  marginal  surface 
of  the  dike  is  unlike  the  groundmass  of  the  main  body  of  the  dike  in 
mineral  composition.  Biotite  is  not  developed,  and  the  only  feldspars  are 
the  microlites  of  plagioclase,  which  may  correspond  to  the  cores  in  the 
lath-shaped  orthoclases  of  the  main  body  of  rock.  As  compared  with  the 
leucite-bearing  I'ock  from  Ishawooa  Canyon  (1698),  it  is  to  be  noted  that 
the  phenocrysts  of  augite  and  olivine  in  the  dike  rock  just  described  are  not 
quite  so  numerous  as  in  the  Ishawooa  rock,  while  there  is  much  more 
augite  in  the  groundmass,  besides  abundant  biotite.  The  microscopic 
crystals  of  feldspar  are  not  so  large  and  distinct,  and  nothing  corre- 
sponding to  leucite  can  be  seen.  Chemically  the  rock  is  richer  in  potash, 
with  about  the  same  per  cent  of  soda.     Alumina  is  slightly  higher,  and 


U.  S.  QEOLOOICAL    SURVEY 


RT    II     PL.   XXXVI 


(B)  X  37 

PHOTOMICROGRAPHS    OF    ABSAROKITE 


THE  HELIOTYPE  PRINTING  CO.,  BOSTON 


ABSAROKITE.  333 

mafj-nesiii  and  lime  are  sli<ihtly  lower.  There  is  a  little  more  silica.  The 
hii^h  loss  on  ig-nitioii  iiulioates  that  there  is  a  hvdrous  silicate  in  thegTouml- 
mass,  possibly  a  zeolite.  As  has  been  pointed  out  in  another  place,^  the 
leucite  in  one  rock  with  abundant  olivine  may  be  represented  by  biotite 
aiid  less  olivine  in  the  other,  with  an  increased  amount  of  orthoclase.  The 
less  distinct  crystallization  of  the  second  rock  prevents  a  perfectly  satis- 
factory comj)arison.  They  illustrate,  however,  what  mineralogical  differences 
may  exist  among  rocks  with  almost  the  same  chemical  compositions. 

The  next  two  rocks  whose  analyses  are  given  still  further  ilhistrate  the 
same  thing.  One  (1277)  is  a  dike  3  feet  wide  on  the  high  ridge  south  of 
Index  Peak  and  of  Clark  Fork  River,  in  places  weathering  out  from  the 
andesitic  breccia  in  a  wall  8  or  10  feet  high,  with  horizontal  columns.  The 
second  (1151)  is  a  surfcial  lava  flow  east  of  the  head  of  Raven  Creek  on 
Mirror  Plateau.  Chemically  they  are  almost  identical,  and  nearly  the  same 
as  the  dike  south  of  Hoodoo  Mountain,  just  described.  They  have  slightly 
less  magnesia,  and  the  lava  flow  has  3.4  per  cent  more  silica  than  the  dike 
rock.     The  latter  experiences  considerable  loss  upon  ignition. 

The  dike  rock  (1277)  is  dark  greenish  gray,  aphanitic,  with  small 
megascopic  phenocrysts  of  augite  and  occasional  large  grains  of  quartz  with 
augite  shells.  The  quartzes  are  cracked  and  filled  with  calcite.  In  thin 
section  the  few  megascopic  crystals  of  augite  are  crowded  with  inclusions 
of  groundmass,  and  resemble  the  augite  phenocrysts  in  the  rock  last 
described.  The  other  constituents  may  be  considered  as  parts  of  the 
groundmass,  which  is  holocrystalline  and  consists  of  much  pale-green  augite, 
brown  biotite,  and  magnetite,  with  a  subordinate  amount  of  feldspathic 
matrix.  There  are  larger  augites  which  are  colorless  at  the  center  and 
gi'een  on  the  margin,  with  a  zonal  structure,  besides  many  small  serpentin- 
ized  olivines.  The  feldspathic  matrix  is  largely  decomposed.  It  is  partly 
lath-shaped  feldspar,  which  is  orthoclase  with  prismatic  cores  of  plagioclase, 
and  often  in  radiating-  groups  suggesting  orthoclase  or  albite-oligoclase. 
Besides  the  recognizable  feldspar  there  is  much  cloudy  microcrypto- 
crystalline  material  with  no  definite  form,  except  a  very  frequent  occurrence 
of  spots  with  an  approach  to  the  outline  of  an  isometric  mineral.  These 
are  often  darker  colored  at  the  center,  and  suggest  the  former  presence  of 

'Iddings,  J.  P.,  The  origin  of  igneous  rocks:  Bull.  PbiloB.  Soc.  Washington,  Vol.  XII,  1892, 
p.  176. 


334     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

leucite.  The  occm-rence  of  leucite  in  similar  rocks  in  this  region  makes 
this  highlv  probable.  In  one  thin  section  of  the  rock  there  is  ranch  trans- 
jjarent  allotriomorphic  mineral,  which  is  in  part  isotropic,  but  is  also  doubly 
refracting.  This  is  undoubtedl)'  analcite.  It  is  probably  secondary,  as  it 
is  found  in  vesicular  cavities,  sometimes  accompanied  by  other  zeolites. 
The  large  rounded  grains  of  quartz  which  occur  sporadically  tln-ough  the 
rock  are  single  iiidividual  crystals  and  not  aggregations.  The  originally 
dihexahedral  form  of  the  crystal,  slightly  rounded,  can  be  seen  on  some  of 
the  individuals,  and  in  the  shape  of  the  cavities  in  the  rock  from  which 
they  may  have  fallen  when  the  rock  was  broken.  They  are  surrounded  by 
a  shell  of  augite  crystals  with  some  brown  altered  glass,  as  in  other  instances 
in  basaltic  rocks.  The  substance  of  the  quartz  is  extremely  pure  and  free 
from  inclusions  of  foreign  matter,  or  of  gas  and  liquid.  In  some  cases 
there  are  a  few  dihexahedral  inclusions  of  altered  groundmass  or  glass. 

This  rock  resembles  that  forming  the  dike  south  of  Hoodoo  Mountain 
in  the  general  character  of  the  groundmass,  except  that  the  phenocrysts  of 
olivine  and  augite  are  almost  microscopic,  and  may  be  considered  part  of 
the  groundmass.  The  ferromagnesiau  minerals  are  about  the  same  in  each, 
and  the  feldspathic  components  are  obscure,  with  indications  of  alkaline 
character. 

The  rock  of  the  lava  flow  east  of  the  head  of  Raven  Creek  (1151,  1152) 
is  dark  gray,  with  abundant  small  megascopic  phenocrysts  of  olivine  and 
augite.  In  thin  section  these  crystals  are  quite  fresh  and  like  those  in  the 
rocks  of  this  class  already  described.  There  is  a  slight  serpentinization  of 
the  olivine.  The  groundmass  consists  of  small  rectangular  prisms  of  ortho- 
clase,  sometimes  with  minute  cores  of  prismatic  labradorite,  besides  abundant 
microscopic  crystals  of  augite  and  magnetite.  There  is  some  serpentine, 
which  occupies  angular  spaces  between  the  feldspar  crystals,  and  may  replace 
glass  base.  The  feldspars  are  distinctly  crystallized,  and  their  orthoclastic 
character  is  unquestionable.  They  resemble  the  orthoclase  crystals  in  the 
leucite-bearing  rock  from  Ishawooa  Canyon.  No  leucite,  however,  was 
observed  in  this  rock.  Only  a  very  small  part  of  the  groundmass  is  lime- 
soda  feldspar.  There  is  no  biotite  and  no  analcite.  Apatite  occurs  in 
delicate  needles.  The  absence  of  biotite  may  be  correlated  with  more  pro- 
nounced orthoclase  and  abundant  olivine,  and  the  absence  of  leucite  accords 
with  the  higher  percentage  of  silica  in  the  i-ock  as  comjmred  with  the  rock 
from  Ishawooa  Canyon. 


ABSAHOlvITE  OF  CACHE  CKEEK.  335 

The  fifth  rock  of  this  chiss,  of  wliic-h  the  chemical  analysis  has  been 
given,  occurs  as  a  massive  body  in  the  andesitic  breccia  on  the  southeast 
fork  of  Cache  Creek.  Another  rock  of  like  character  forms  a  narrow  dike 
on  the  divide  between  Cache  and  Crandall  creeks  (1282,  1283).  They  are 
a})hanitic,  l)ro\vnish-gray  rocks,  without  phenocrysts,  but  having-  minute 
brown  pseudomor])hs,  presumably  after  olivine.  The  rocks  are  identical  in 
every  respect  and  carry  occasional  rounded  grains  of  dark-colored,  crackled 
quartz,  inclosed  in  a  thin  g-reen  shell. 

In  thin  section  these  rocks  are  holocrystalline  and  fine  grained,  con- 
sisting of  thin  lath-shaped  feldspars,  frequently  grouped  in  fan-like  clusters. 
They  are  not  distinctly  striated,  and  are  probably  orthoclase.  Others  are 
plagioclase  with  low  angles,  and  some  are  irregularly  bounded  and  obscure. 
This  matrix  is  crowded  with  idiomori)hic  crystals  of  pale-green  augite, 
dark-brown  biotite,^  and  magnetite,  the  ferromagnesian  minerals  equaling 
the  feldspar  in  amount.  There  are  a  few  porphja-itical  augite  groups, 
which  are  almost  colorless  at  the  ceiiter,  with  pale-green  margins.  The 
pseudomorphs  have  the  outline  of  olivine.  The  feldspars  exhibit  slight 
alteration,  but  the  augites  and  biotites  are  perfectly  fresh.  In  places  there 
are  ilmenite  rods. 

There  is  considerable  serpentine  scattered  through  the  rock  in  small 
aggregations  of  pale-green  spherulites.  Miueralogically  the  rock  is  very 
similar  to  the  quartz-bearing  dike  rock  (1277)  from  the  ridge  southeast  of 
Index  Peak,  which  it  resembles  megascopically.  Chemically  it  is  slightly 
higher  in  alumina  and  potash,  and  slightly  lower  in  magnesia  and  lime. 
The  high  loss  on  ignition  is  most  likely  due  to  the  serpentine,  which  was 
probably  derived  from  olivine. 

Fortunately,  this  phase  of  the  magma  is  found  in  immediate  connection 
with  the  gabbro  core  on  Hurricane  Mesa,  Crandall  Basin.  It  forms  the 
dense  bluish-black  margin  (1422)  of  a  4-foot  dike,  the  middle  of  which  is 
gray  and  crystalline  (1421).  The  dike  cuts  granular  rock  near  the  base  of 
the  middle  spur  of  the  core.  The  aphanitic  marginal  rock  (1422)  carries  a 
few  small  micas,  but  no  prominent  phenocrysts.     In  thin  section  it  has  the 

'  When  first  studied,  some  of  the  brown  minerals  were  considered  to  be  brown  hornblende,  but 
a  careful  review  fails  to  establish  the  presence  of  hornblende.  Some  of  the  biotite  plates  are  long 
and  narrow,  and  when  they  overlie  a  crystal  of  feldspar  they  appear  to  possess  a  double  refraction  not 
found  in  other  biotite  plates,  which  led  to  their  being  mistaken  for  hornblende.  The  rock  was  doubt- 
fully named  hornblende-minette  in  the  list  of  rocks  whose  analyses  were  given  in  Table  III  in  the 
paper  on  The  origin  of  igneous  rock,  in  Hull.  Philos.  Soe.  Washington,  Vol.  XII,  p.  199. 


336  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

same  habit  as  the  rock  last  described,  consisting  of  colorless  feldspar 
crowded  with  idiomorphic  crystals  of  pale-green  augite,  brown  biotite,  and 
magnetite,  which  predominate  over  the  feldspar.  Thei'e  is  a  little  brownish- 
green  hornblende,  and  many  paramorphs  of  olivine,  the  centers  of  which  in 
some  cases  are  surrounded  by  a  border  of  magnetite,  and  outside  of  this, 
biotite.  Along  a  seam  in  the  rock  there  is  much  secondary  green  horn- 
blende, which  replaces  the  pyroxene  for  some  distance  on  both  sides  of  the 
seam.  The  feldspar  matrix  has  a  variable  structure  and  is  perfectly  fresh. 
In  places  it  consists  of  comparatively  long  and  broad  individuals  of  unstriated 
feldspar  with  low  double  refraction  and  almost  parallel  extinction,  which  is 
presumably  orthoclase.  These  prisms  are  clustered  in  radiating  groups 
inclosing  the  feiTomagnesian  minerals,  the  cementing  feldspar  prisms  being 
much  larger  than  the  other  minerals.  In  other  parts  of  the  section  the 
feldspars  are  small,  lath-shaped  in  some  cases,  and  granular  in  others. 
None  of  the  feldspar  is  distinctly  striated. 

The  rock  from  the  middle  of  the  dike  (1-^21)  differs  considerably  from 
that  of  the  margin.  In  thin  section  it  is  seen  to  be  more  feldspathic  and  is 
coarser  grained.  The  feldspar  is  mostly  striated  plagioclase  with  borders 
of  orthoclase.  The  plagioclase  kernels  are  sometimes  altered  and  cloudy. 
There  is  a  very  little  quartz.  The  microstructure  of  the  rock  is  produced 
by  ill-defined  lath-shaped  crystals  and  some  grains.  There  is  considerable 
augite,  changed  to  uralite,  much  bicitite,  little  magnetite,  and  numerous 
paramorphs  of  olivine.  It  is  probable  that  there  was  some  primary  horn- 
blende in  the  rock  before  iiralitization  set  in.  The  margin  of  the  dike  is 
richer  in  ferromagnesian  minerals  and  magnetite,  and  the  feldspars  are 
more  alkaline  and  represent  a  phase,  of  differentiation  of  the  gabbro 
magma  brought  about  within  the  dike. 

Rocks  from  other  parts  of  this  region  which  are  like  those  just  described 
in  mineral  composition  and  structure  are  the  following:  Massive  lavas 
associated  with  basic  andesitic  breccia  at  Signal  Point  on  Yellowstone  Lake 
(1617, 1618,  1619),  corresponding  to  the  lava  flow  (1151)  east  of  the  head 
of  Raven  Creek.  One  modification  (1618)  has  much  orthoclase  in  the 
groundmass  and  little  lime-soda  feldspar,  and  contains  crystals  of  isotropic 
or  faintly  doubly  refracting  mineral  clouded  yellowish  in  transmitted  light, 
which,  from  analogy  with  similar  olivine-augite-orthoclase  rocks  from  this 
region,  is  or  was  most  probably  leucite.    Brown  biotite,  probably  secondary, 


ABSAROKITE  OF  TWO  OCEAN  PASS.  337 

and  needles  of  apatite  complete  the  resemblance  between  this  rock  and  that 
just  referred  to.  It  appeal's  to  be  an  intermediate  variety  between  the 
latter  and  certain  orthoclase-bearing  basaltic  rocks  from  the  head  of  Conant 
Creek,  to  be  described  presently  (p,  338).  Its  appearance  in  this  section  is 
shown  in  PI.  XXXVI,  fig.  2. 

Another  modification  of  the  lava  at  Signal  Point  (1617)  contains  much 
orthoclase  in  the  groundmass,  no  isotropic  mineral,  but  considerable  reddish 
brown  mica,  which  appears  to  be  secondary  and  accompanies  chlorite  or 
serpentine.  It  is  sometimes  shaqoly  idiomorphic,  and  has  a  small  axial 
angle.  There  is  also  some  red  oxide  of  iron.  Another  variety  has  a  nearly 
opaque  groundmass,  with  reddish-brown  color,  carrying  phenocrysts  of 
augite  and  olivine  like  those  in  the  rocks  associated  with  it.  In  very  thin 
section  the  groundmass  is  seen  to  contain  much  iron  oxide  and  feldspathic 
mineral,  partly  in  lath-shaped  microlites,  altered  to  faintly  doubly  refract- 
ing substance.  The  rock  is  undoubtedly  a  somewhat  altered,  opaque, 
scoriaceous  modification  of  this  kind  of  rock. 

The  massive  lava  flows  at  Two  Ocean  Pass  belong  in  part  to  this  same 
class  of  rocks,  but  vary  somewhat  in  composition  in  the  different  sheets, 
which  directly  ovei'lie  one  another.  The  rock  most  closely  resembling  those 
just  described  forms  the  second  sheet  from  the  bottom  (1720,  1721).  Its 
chemical  composition  is  shown  in  analysis  6,  p.  329.  It  contains  similar 
phenocrysts  of  augite  and  olivine,  with  none  of  feldspar.  The  feldspar  of 
the  groundmass  is  almost-  wholly  orthoclase,  sometimes  in  simjile  jjrismatic 
crystal,  sometimes  in  Carlsbad  twins.  It  is  nearly  idiomorphic.  There  is 
a  small  amount  of  isotropic  mineral  as  interstitial  filling  between  orthoclase 
prisms.  It  has  a  slightly  lower  index  of  refraction.  It  may  possibly  be 
glass.  The  groundmass  also  contains  augite,  magnetite,  serpentine,  red- 
brown  biotite,  and  needles  of  apatite.  No  lime-soda  feldspar  was  observed. 
The  groundmass  is  holocrystalline,  the  average  size  of  the  component  ortho- 
clase being  about  0.07  mm.  wide  by  0.14  mm.  long.  Chemically  it  differs 
from  the  most  typical  absarokite  by  being  higher  in  alumina  and  lower  in 
magnesia,  approaching  shoshonite  in  chemical  composition,  with  which  rock 
it  is  associated  in  the  field. 

The  scoriaceous  portion  of  this  rock  (1721)  is  almost  opaque  in  thin 
section,  and  in  very  thin  edges  is  seen  to  consist  of  minute  crystals  of  mag- 
netite, pyroxene,  and  a  feldspathic  mineral  whose  character  is  not  recogniz- 

MON  XXXII,  PT  II 22 


338     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

able.  The  rock  of  the  sheet  immediately  overlying  this  one  is  very  vesicular 
(1718,  1719)  and  carries  few  phenocrysts.  In  thin  section  it  is  extremely 
fine  grained,  and  consists  of  microlites  of  feldspar,  augite,  and  magnetite. 
The  feldspars  are  prisms  of  lime-soda  feldspar  with  outer  zones  of  orthoclase. 

Modifications  of  these  rocks  in  which  the  lime-soda  feldspar  cores 
within  the  orthoclase  are  more  frequent  and  larger,  and  which  constitvite 
transitional  varieties  between  absarokite  and  basalts  rich  in  olivine  and 
augite,  occur  in  the  breccia  soutli  of  the  head  of  Conant  Creek.  Thev 
have  abundant  small  phenocrysts  of  augite  and  serjDentinized  olivine  (1745), 
the  same  minerals  occurring  in  the  groundmass  with  magnetite  and  consid- 
erable feldspar.  There  is  much  red  oxide  of  iron  through  the  mass  in  thin 
fibers  and  as  coatings  of  the  smallest  augites,  magnetites,  and  olivine  pseu- 
domorphs.  The  microscopic  feldspars  are  nearly  idiomorphic,  though  the 
rock  is  holocrystalline.  They  are  rectangular,  partly  tabi;lar,  partly  pris- 
matic, and  consist  of  a  central  idiomorphic  crystal  of  lime-soda  feldspar 
with  polysynthetic  twinning  and  higher  refraction  than  the  marginal  zone, 
which  is  not  striated,  but  is  in  Carlsbad  twins.  The  relative  sizes  of  these 
two  parts  of  each  complex  crystal  are  variable.  In  some  cases  the  kernel 
exceeds  the  shell;  in  others,  the  reverse.  The  outer  portion  is  oi'thoclase; 
the  inner  feldspar  is  labradorite.  The  latter  is  clouded  with  minute  specks 
or  inclusions;  the  orthoclase  is  quite  pure.  There  is  a  little  light-brown 
mica.  Other  breccias  north  of  this  consi.st  largely  of  basalts  somewhat 
related  (1747  to  1750).  They  are  characterized  by  phenocrysts  of  augite 
and  olivine,  without  any  of  feldspar.  Augite  and  olivine  both  contain  glass 
inclusions,  often  in  abundance,  and  the  augite  incloses  olivine.  The  augite 
is  pale  brownish  green,  sometimes  with  zonal  structure ;  the  olivine  is  color- 
less. The  groundmass  is  the  same  as  in  the  rock  from  near  the  head  of 
Conant  Creek  (1745),  but  is  finer  gi-ained. 

A  similar  rock  occurs  west  of  Glade  Creek  on  Coulter  Creek  (1743). 
The  augite  and  olivine  phenocrysts  are  freer  from  inclusions.  The  groiind- 
mass  is  holocrystalline  and  consists  of  labradorite  and  orthoclase,  augite, 
some  serpentinized  olivine,  serpentinized  prisms  that  probably  were  ortho- 
rhombic  pyroxene,  magnetite,  and  thin  needles  of  apatite.  There  is  a  very 
little  brown  mica. 

Intennediate  between  absarokite  and  shoshonite  are  rocks  (1623)  that 
are  dark  gray  with  a  waxy  luster,  which  have  abundant  phenocrysts  of 


DISTIUBUTION  OF  SHOSHONITE.  339 

oli^^ne  and  augite,  with  fewer  of  labradorite.  They  are  holocrj'-stalHne  and 
consist  of  plagiodase  with  orthoclase  and  some  analcite,  besides  augite, 
magnetite,  and  delicate  needles  of  aj^atite. 

SIIOSirONITE. 

The  rocks  classed  as  shoshonites  are  more  numerous  than  the  absarokites, 
and  eyibrace  a  somewhat  wider  range  of  composition.  They  occupy  the 
middle  ground,  as  it  were,  in  this  series,  and  pass  by  gradual  transitions  into 
absarokite,  banakite,  and  the  normal  basalts  of  the  region.  They  occur 
associated  with  absarokite,  and  consequently  at  the  same  localities.  Their 
principal  occurrences  are  on  the  Lamar  River,  Mirror  Plateau,  in  Crandall 
Basin,  in  the  Stinkingwater  and  Ishawooa  canyons,  on  the  southeast  fork 
of  Beaverdam  Creek,  and  at  Two  Ocean  Pass,  one  of  the  heads  of  the 
Shoshone  or  Snake  River.  This  is  the  locality  from  which  the  rock  was 
fii-st  collected  and  identified  as  an  orthoclase-basalt.  The  rock  also  occvu's 
on  Grayling  Creek  and  west  of  The  Crags,  southwest  of  Gallatin  Mountains. 
Most  of  the  rocks  are  characterized  by  ^^rominent  phenocrysts  of  labrador- 
ite, together  with  those  of  augite  and  olivine.  A  few  are  without  feldspar 
phenocrysts,  but  quite  a  number  are  without  megascopic  phenocrysts  and 
are  correlated  with  the  porphyritic  forms  on  chemical  as  well  as  mineral- 
ogical  grounds.  A  small  number  are  leu  cite  bearing.  The  chemical  com- 
positions of  eight  of  these  rocks  are  given  in  the  following  table.  To 
these  are  added  three  analyses  of  transitional  varieties.  The  analyses  are 
arranged  so  as  to  bring  those  most  alike  by  the  side  of  one  another.  As 
already  said,  the  mineralogical  variations  range  from  an  abundance  of 
olivine  and  augite  to  a  paucity  of  them,  which  corresponds  to  the  chemical 
variation  from  higher  magnesia  and  lime  to  lower  magnesia  and  lime, 
and  the  coiTesponding  changes  in  the  alumina  and  alkalies  in  the  opposite 
direction.  In  describing  these  rocks  those  that  are  chemically  and  mineral- 
ogically  alike  will  be  considered  first,  and  afterwards  those  that  are  chemically 
alike  but  minera  logically  different. 


340  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Analyses  of  shoshonites  and  transitional  rocks. 


Constituent. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

SiO.2 

50.06 

51.75 

53.49 

52.86 

52.49 

54.86 

56.05 

54.97 

50.99 

52.11 

53.71 

TiO.2 

.51 

.86 

.71 

1.04 

.81 

.69 

.98 

.97 

.67 

.53 

.74 

AljOa  .... 

17.00 

17.48 

17.19 

17.51 

17.89 

17.28 

19.70 

18.38 

15.62 

16.58 

18.00 

FeiOs  .... 

2.96 

6.42 

4.73 

5.18 

5.76 

4.08 

3.74 

3.06 

8.47 

3.66 

3.99 

FeO  

5.42 

1.46 

3.25 

3.31 

2.08 

2.28 

2.32 

4.22 

1.43 

4.99 

4.05 

MnO 

.14 

Trace. 

.14 

Truce. 

.09 

.19 

Trace. 

Trace. 

Trace. 

.23 

.24 

NiO 

.07 

BaO 

.06 
4.42 

4.18 

.30 
3.49 

.37 
4.19 

MgO 

3.61 

4.05 

2.51 

2.38 

5.23 

6.87 

5.19 

CaO 

8.14 

8.20 

6.34 

6.51 

7.01 

5.42 

4.34 

5.43 

6.53 

6.43 

6.88 

Li'O 

Trace. 
3.33 

3.23 

.04 
3.22 

.03 
3.45 

Na;0 

3.53 

3.18 

3.94 

3.29 

3.39 

3.25 

3.50 

KjO 

3.40 

3.72 

3.86 

3.41 

3.73 

3,96 

4.44 

3  37 

3.05 

3.20 

3.10 

P.O5 

.66 

.67 

.43 

.53 

.55 

.48 

.66 

.42 

.53 

.63 

.38 

CI 

Trace. 
.17 

.16 
.22 

Trace. 

.03 

2.92 

.82 

SO3 

CO. 

HjO 

4.85 

2.26 

2.17 

1.76 

2.63 

2.16 

1.86 

3.87 

1.99 

.55 

100. 28 

100. 37 

100. 02 

99.93 

100. 01 

99.90 

100. 14 

100.45 

99.85 

100. 47 

100.  33 

1.  Shoshonite,  lava  sheet,  Lamar  River,  .south  of  Bisou  Peak.    Analyst,  L.  6.  Eakins.     (1131.) 

2.  Shoshonite,  lava  floTV,  northeast  base'of  Sepulchre  Mouutaiu.    Analyst,  J.  E.  Whitfield.     (379.) 

3.  Shoshonite,  lava  sheet,  southeast  fork  of  Beaverdara  Creek.     Analyst,  L.  G.  Eakins.     (1647.) 

4.  Shoshonite,  lava  sheet,  southeast  fork  of  Beaverdam  Creek.    Analyst,  J.  E.  Whitlield.    (1651.) 

5.  Leucite-shoshonite,  lava  sheet,  mountain  cast  of  Pyramid  Peak.   Analyst,  L.  G.  Eakins.  (1476.) 

6.  Olivine-free  shoshonite,  dike  northeast  of  Indian  Peak.     Analyst,  L.  G.  Eakins.     (1316.) 

7.  Shoshonite,  lava  sheet.  Two  Ocean  Pass.     Analyst,  J.  E.  AVhitfield.     (1715.) 

8.  Shoshonite,  summit  of  Baldy  Mountain,  Bear  Gulch,  Montana.     Analyst,  J.  E.  Whitfield. 

9.  (?)  Hornblende.hasalt,  dike  near  head  of  Stinkingwater  Canyon.     (1462.) 

10.  Orthoclase-bearing  basalt,  dike,  ridge  south  of  Hurricane  Mesa.     (1325.) 

11.  Orthoclase-bearing  gabbro,  core.  Hurricane  Mesa,  Crandall  Basin.     (1430.) 

The  rock  whose  chemical  composition  is  shown  by  the  first  analysis  is 
exposed  as  a  sui-ficial  lava  flow  at  the  base  of  Bison  Peak  on  Lamar  River 
(1131).  It  is  dark  gray,  with  a  waxy  luster,  and  cames  abundant  pheno- 
crysts  of  labradorite,  augite,  and  olivine,  and  some  small  amygdules  of 
zeolite  and  calcite.  In  thin  section  it  is  holocrystalline,  the  groundmass 
consisting  of  lath-shaped  lime-soda  feldspar  and  considerable  orthoclase  in 
zones  surrounding  the  plagioclase  microlites  and  also  in  twinned  prisms, 
besides  augite,  magnetite,  and  a  little  serpentine.  The  plienocrysts  of 
labradorite  are  twinned,  with  very  nan-ow  lamellae.     Those  of  augite  and 


SHOSHONITE.  341 

olivine  are  like  the  phenociysts  of  these  minerals  in  absarokite;  the  olivine 
is  partly  serpentinized. 

Similar  lava  occnrs  at  the  north  base  of  Specimen  Ridge  (1127).  In 
this  the  i^henoorvsts  of  feldspar  are  labradorite  with  about  the  composition 
Ana  AUj.  The  groundinass  is  partly  globulitic  and  microlitic  glass,  contain- 
ing many  rectangular  orthoclase  crystals  Avith  lath-shaped  lime-soda  feld- 
spars at  their  center,  some  of  which  prove  to  be  labradorite  (Aug  Aba) ;  niost 
of  them  exhibit  low  angles,  and  may  be  andesine-oligoclase.  Some  small 
rectangular  ])lagi()clases  without  orthoclase  margins  are  labradorite  (Aug  Abj). 
There  is  nearly  as  much  orthoclase  as  plagioclase  in  the  groundmass. 
There  is,  of  course,  augite,  apatite,  and  magnetite,  as  in  the  other  rocks. 
Other  modifications  of  this  rock  have  a  less  highly  crystallized  groundmass, 
m  which  orthoclase  has  not  been  developed.  Such  forms  could  not  be 
distinguished  microscopically  from  some  ordinary  basalts.  Other  rocks 
of  this  type  with  glass)'  and  microlitic  groundmasses  occur  at  the  creek 
south  of  Opal  Creek  (1143  \  and  iu  a  cliff  3  miles  up  Soda  Butte  Creek  (1137). 
A  holocrystalline  rock  of  this  character  forms  a  dike  on  Timber  Creek, 
Crandall  Basin  (1328).  Another  forms  a  lava  flow  on  the  mountain  east 
of  Pyramid  Peak  (1474,  also  1457).  A  modification  with  small  pheno- 
crysts  occurs  as  a  surface  flow  at  tlie  falls  of  Timothy  Creek  on  MiiTor 
Plateau  (1153),  and  elsewhere  on  this  plateau  (1155),  and  is  exposed  in 
association  with  andesitie  breccia  beneath  rhyolite  west  of  The  Crags, 
southwest  of  Gallatin  Mountains  (580).  It  has  also  been  found  in  bowlders 
east  of  the  lower  Geyser  Basin. 

Another  basaltic  rock  belonging  to  this  class  because  of  its  chemical 
composition  occurs  in  an  obscure  exposure  at  the  north  base  of  Sepulchre 
Mountain.  It  appears  to  have  been  a  surficial  flow  of  lava  contemporaneous 
with  the  acid  andesitie  breccias  at  that  place.  It  is  dark  greenish  gray 
(379,  381),  with  few  megascopic  phenocrysts  of  augite  and  serpentinized 
olivine,  and  without  any  of  feldspar,  and  is  vesicular,  with  amygdules  of 
agate  and  quartz.  In  thin  section  it  is  holocrystalline,  with  lath-shaped 
plagioclase  microlites  sun-ounded  by  a  zone  of  orthoclase,  which  is  in  con- 
siderable amount.  There  are  also  prisms  of  augite  and  crystals  of  magnetite. 
Apatite  needles  are  abundant.  Its  chemical  composition  is  shown  in  the 
second  analysis  of  the  table  just  given.  It  resembles  the  first  one  closely 
except  in  the  oxidation  of  the  iron.  The  lime-soda  feldspars  are  confined 
to  the  groundmass,  in  the  form  of  microlites. 


342     GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PAEK. 

The  rock  whose  chemical  composition  is  given  in  the  third  aiid  fourth 
analyses  occurs  as  a  massive  sheet  beneath  another  of  very  similar  character 
on  the  southeast  fork  of  Beaverdam  Creek.  It  is  dark  purplish  gray,  with 
niunerous  phenocrysts  of  labradorite,  augite,.  and  serpentinized  olivine 
(1647,  1648,  and  1651).  A  lighter-colored  modification  (1649)  carries  por- 
phyritical  biotite  and  white  amygdules  of  zeolite.  In  thin  section  it  is 
holocrystalline,  and  resembles  closely  the  rock  from  the  south  base  of  Bison 
Peak  (1131),  except  that  the  olivine  is  serpentinized.  The  groundmass  is 
similar  and  there  is  considerable  orthoclase.  In  the  variety  with  biotite 
there  are  cloudy  isotropic  patches,  which  may  be  analcite.  The  massive 
lava  immediately  overlying  it  is  similar  in  general  appearance,  but  contains 
leucite,  and  will  be  described  later  in  connection  with  the  banakites. 

The  rock  whose  chemical  composition  is  given  by  analysis  5  is  a 
massive  surficial  flow  on  the  tojj  of  the  mountain  east  of  Pyramid  Peak, 
resembling  in  general  appearance  the  lava  flow  from  the  same  place  already 
cited  as  similar  to  that  from  the  base  of  Bison  Peak,  but  the  phenocrysts 
are  fewer  and  smaller.  (1475,  1476).  The  two  specimens  collected  differ 
slightly  in  grain.  They  are  holocrystalline  and  very  fine  grained,  with  an 
abundance  of  augite  and  magnetite  microlites  in  the  groundmass.  The 
feldspars  are  minute  lath-shaped  crystals  and  allotriomorphic  grains,  with 
low  double  refraction.  There  are  spots  where  minute  gi'ains  of  augite  and 
magnetite  are  clustered  together  and  are  inclosed  in  a  yellowish  substance 
which  is  almost  isotropic  and  has  the  outline  of  leucite.  These  impure 
leucites  are  scattered  through  the  rock  and  are  not  very  numerous.  They 
are  very  small  and  can  not  be  more  definitely  identified.  Their  outline 
and  inclusions  are  characteristic.  The  groundmass  carries  irregular  patches 
of  light-brown  mica,  small  phenocrj^sts  of  augite  and  serpeiTtinized  olivine, 
and  still  fewer  larger  crystals  of  augite  and  olivine.  It  is  a  leucite-bearing 
modification  of  this  magma  without  any  chemical  differences  in  composition. 

The  rock  of  analysis  6  (1316)  is  from  an  18-inch  dike  on  the  ridge 
northeast  of  Indian  Peak.  It  is  gray  and  aphanitic,  with  abundant  small 
phenocrysts  of  augite  and  hme-soda  feldspar,  with  rather  low  extinction 
angles.  In  thin  section  it  is  seen  to  be  holocrystalline  and  very  fine  grained, 
consisting  of  indistinctly  outlined  feldspar  microlites,  in  part  alkaline,  with 
low  double  refraction  and  no  polysynthetic  twinning.  There  is  a  subordinate 
amount  of  idiomorphic  microlites  of  biotite,  prisms  of  augite,  and  grains  of 


SHOSIIONITE  OF  TWO  OCEAN  PASS.  343 

niaficnetite.     There  is  no  olivine,  and  it  is  this  fact  which  chiefly  distinguishes 
it  from  the  other  varieties  of  these  rocks. 

Another  (hke  (13 IS)  in  the  same  phace  resembles  the  one  just  described 
in  mineral  composition,  except  tliat  the  only  phenocrysts  are  small  augites. 
Two  other  dike  rocks  in  this  vicinity  (1344,  13,54)  are  like  these  in  mineral 
composition,  with  phenocrysts  of  labradorite  and  augite,  but  none  of 
olivine.  In  one  case  (1344)  the  microlites  of  plagioclase  ai'e  suiTounded 
by  orthoclase  margins. 

The  rock  of  the  seventh  analysis  (1715)  is  the  uppermost  of  the  five 
surficial  lava  sheets  that  overlie  one  another  at  Two  Ocean  Pass.  It  is 
dark  gray,  with  a  waxy  luster,  and  carries  scattered  phenocrysts  of  feldspar 
and  serpentinized  olivine.  In  thin  section  the  groundmass  is  seen  to  be 
holocrystalline,  and  is  composed  of  orthoclase  crystals,  both  idiomorphic 
and  allotriomorphic,  with  much  magnetite  and  augite  and  some  chlorite  or 
serpentine,  with  red-brown  biotite  and  hair-like  needles  of  apatite.  There 
are  comparatively  large  but  microscopic  dusted  apatites  among  the  pheno- 
crysts, showing  this  mineral  in  two  generations.  The  large  apatites  are 
comparatively  abundant,  and  were  in  part  inclosed  in  the  olivine,  which  is 
wholly  serpentinized.  The  feldspar  phenocrysts  are  labradorite,  with  highly 
developed  polysyuthetic  twinning.  Several  crystals  are  clustered  together 
into  groups.  In  the  rock  of  the  second  sheet  (1716)  the  feldspar  pheno- 
crysts are  labradorite-bytownite,  being  decidedly  basic,  with  high  extinc- 
tion angles  and  relatively  strong  double  refraction.  Rectangular  inclusions, 
probabl}^  feldspar,  are  numerous;  also  considerable  magnetite  and  augite, 
and  some  serpentine.  The  groundmass  is  like  that  of  the  top  sheet,  except 
that  the  orthoclase  crystals  sometimes  have  a  small  nucleus  of  lime-soda 
feldspar.  These  nuclei  are  sometimes  colored  green  from  sei-peutine,  when 
they  are  easily  confounded  with  partly  altered  pyroxene.  In  other  respects 
the  rock  is  like  the  uppermost  sheet.  The  rock  of  one  of  these  sheets 
(1724)  on  the  north  side  of  Pacific  Creek,  2  miles  west  of  Two  Ocean  Pass, 
is  like  the  one  last  described,  with  somewhat  larger  phenocrysts  of  labra- 
dorite, 5  mm.  long.  They  have  the  same  character  and  inclusions  as  the 
labradorite  phenocrysts  of  the  last-mentioned  rock.  The  olivines  are 
entirely  altered  to  serpentine.  The  groundmass  has  the  same  composition 
and  structure.  Some  serpentine  in  the  groundmass  occupying  spaces 
between  idiomorphic  orthoclases  may  replace  small  interstitial  bits  of  glass; 


344     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

otherwise  the  rock  appears  to  be  holocrystalline.  In  one  specimen  (1714) 
there  is  less  serpentine,  and  considerable  colorless  mineral  with  lower 
refraction  than  orthoclase,  which  is  not  isotropic,  but  has  weak  double 
refraction.  The  microstructure  of  this  rock  and  the  character  of  the  large 
feldspar  phenocrysts  are  shown  in  PI.  XXXVII,  fig.  1. 

The  rocks  of  the  other  two  sheets  (1717  to  1719)  are  scoriaceous  and 
vesicular,  and  are  microlitic  with  much  opaque  mineral.  They  are  some- 
what altered,  and  their  exact  mineral  composition  can  not  be  made  out. 
They  are  related  in  general  character  to  the  rocks  associated  with  them.  A 
rock  of  the  same  kind  as  the  more  cr3^stalline  forms  from  Two  Ocean  Pass 
is  found  on  Fox  Creek  (1731).  Shoshonite,  quite  like  that  at  Two  Ocean 
Pass,  with  pronounced  orthoclase  in  the  groundmass,  but  carrying  pheno- 
crysts of  hypersthene  and  augite  and  less,  olivine,  with  large  labradorites, 
occurs  west  of  the  summit  of  Baldy  Mountain,  east  of  Bear  Gulch,  just 
north  of  the  Yellowstone  Park.  Its  chemical  composition  is  shown  in 
analysis  8.  It  is  low  in  magnesia  and  is  chemically  more  like  the  sho- 
shonite of  Two  Ocean  Pass  than  the  others.  There  are  no  carbonates 
discoverable  in  the  thin  section  of  the  rock  corresponding  to  the  consider- 
able percentage  of  carbon  dioxide  in  the  analysis.  Tlie  rock  is  very  fresh, 
and  it  is  possible  that  the  material  analyzed  contained  fragments  of  limestone 
or  of  calcite. 

Ver}-  similar  rocks  occur  on  Lamar  River  2  miles  above  the  mouth  of 
Slough  Creek  (1129),  and  also  a  short  distance  below  the  mouth  of  Soda 
Butte  Creek  (1136,  1 135).  They  are  sm-ficial  lava  sheets  and  have  pheno- 
crysts of  feldspar  and  very  small  ones  of  augite  and  olivine  The 
groundmass  is  nearly  the  same  as  that  just  described.  Other  rocks  like 
the  last  named  are  from  the  spur  of  Mirror  Plateau  south  of  Flint  Creek 
(1147),  and  from  the  north  side  of  Grayling  Creek  west  of  the  end  of 
Crowfoot  Ridge  (578),  and  from  a  point  west  of  The  Crags  (579).  All 
of  these  were  lava  flows  that  poured  out  upon  the  surface  of  the  earth. 

A  comparison  of  the  chemical  analyses  and  of  the  rocks  of  this  group, 
besides  making  evident  the  relationships  already  noted,  also  shows  what 
mineralogical  difi'erences  may  obtain  for  rocks  of  nearly  the  same  chemical 
composition.  Some  of  these  diff"erences  have  already  been  described  in  the 
case  of  the  leucite-bearing  varieties.  Other  differences  may  be  mentioned. 
The  lava  flow  from  the  southeast  fork  of  Beaverdam  Creek  (1647)  and  the 
dike  rock  from  the  ridge  northeast  of  Indian  Peak,  though  nearly  alike 


U.  S.  GEOLOGICAL    SURVEY 


MONOGRAPH     XXXII      PART    II      PL.    XXXVII 


( B)  %   36 

PHOTOMICROGRAPHS    OF  SHOSHONITE    AND    DIORITE-PORPHYRY 


THE  HELIOTYPE  PRINTING  CO.,  BOSTON 


ROCKS  KELATKD  TO  SHOSUONITES.  345 

chemically  (analyses  3,  4,  and  6),  are  quite  unlike  niineralogically.  The 
first  has  abundant  phenocrysts  of  labradorite,  olivine,  and  augite,  Avhile 
the  second  contains  no  olivine.  The  g-roundmass  of  the  first  contains 
some  brown  mica  which  may  be  secondar}',  while  that  of  the  second  con- 
tains much  mica  that  is  primary.  Other  differences  will  appear  when  sev- 
eral rocks  which  are  closely  related  to  shoshonites  have  been  described. 
The  chemical  analyses  of  three  of  these  are  appended  to  the  table  on 
p.  340 — Nos.  9,  10,  and  11.  These  rocks  are  not  so  different  chemically 
from  normal  basalts,  except  that  alkalies  are  rather  higher,  and  potash  is 
sjjecially  so.  The  alkalies  are  like  those  in  analyses  1  to  5;  magnesia  is 
higher  than  in  shoshonites,  and  more  nearly  that  of  normal  basalts. 

Analvsis  9  is  of  a  dike  rock  from  near  the  head  of  Stinkinsrwater 
River  (1462).  The  rock  is  very  dark  gra}-,  with  long  megascopic  crystals 
of  hornblende,  and  some  of  augite,  but  none  of  feldspar.  In  thin  section 
it  is  holocrystalline.  The  groundmass  is  composed  of  lath-shaped  plagio- 
clase  with  low  extinction  angles  and  of  cryptocrystalline  material,  probably 
an  alteration  product,  besides  augite  and  magnetite,  and  considerable  serpen- 
tine, which  is  evidently  the  alteration  product  of  small  olivines  whose  origi- 
nal form  is  still  preserved.  The  phenocrysts  are  large  hornblendes  with 
irregular  outlines  and  a  border  of  magnetite  grains,  and  smaller  augites. 
,  There  are  none  of  feldspar.  The  rock  might  be  called  a  honi}:)]ende-basalt, 
with  feldspar  averaging  about  the  composition  of  oligoclase.  It  is  possible 
that  some  orthoclase  may  exist  in  the  groundmass,  but  it  was  not  recog- 
nized in  the  rock  section.  The  shoshonite  nearest  to  this  rock  in  chemi- 
cal composition  is  the  lower  sheet  from  the  southeast  fork  of  Beaverdam 
Creek  (1647),  analyses  3.  It  differs  from  it  raineralogically  in  not  having 
hornblende,  in  having  large  phenocrysts  of  labradorite,  and  in  the  presence 
of  orthoclase  in  the  groundmass. 

The  rock  whose  composition  is  given  in  analysis  10  is  a  basalt-like 
lava,  forming  large  blocks  in  the  basic  breccia  on  the  ridge  south  of  the 
core  of  Crandall  volcano  (1325).  It  carries  large  phenocrysts  of  labradorite- 
bytownite,  and  abundant  ones  of  olivine  and  augite.  The  groundmass  is 
holocrystalline,  and  consists  of  irregularly  lath-shaped  feldspars  that  are 
labradorite  at  the  center  and  orthoclase  in  the  margin.  Orthoclase  is  in 
subordinate  amount.  Augite,  magnetite,  and  some  serpentine,  with  delicate 
needles  of  apatite,  are  the  other  constituents.  It  is  like  the  shoshonites 
already  described,  but  is  richer  in  labradorite. 


346     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  TAEK. 

Analysis  11  is  that  of  a  hypidiomorpliic  granular  pyroxene-diorite  or 
gabbro  (1430)  from  the  volcanic  core  on  Hurricane  Mesa,  Crandall  Basin. 
It  consists  of  crystals  1  or  2  mm.  in  diameter,  which  are  labradorite- 
bytownite,  nearly  idiomorphic,  a  moderate  amount  of  orthoclase,  always 
allotriomorphic,  and  a  very  little  quartz,  besides  much  augite  with  diallagic 
character,  some  hypersthene,  considerable  biotite  and  magnetite,  with 
apatite  and  a  few  serpentinized  crystals  of  olivine.  The  structure  and 
microscopical  characters  are  the  same  as  those  of  the  gabbro  of  this  volcanic 
core,  which  are  fully  described  in  Chapter  VII.  The  orthoclase  does  not 
form  a  margin  around  the  crystals  of  labradorite,  but  occurs  as  independent 
crystals. 

Transitional  varieties  between  shoshonite  and  the  normal  basalt  of  the 
region  are  numerous.  Chemically  they  are  recognized  by  lower  percent- 
ages of  alkalies  and  higher  magnesia.  Mineralogically  they  are  recognized 
in  the  more  crystalline  forms  by  the  smaller  amount  of  orthoclase  margins 
to  the  labradorite  crystals;  but  in  the  less  crystalline  forms,  where  the 
groundmass  is  partly  glassy,  or  where  the  feldspar  microlites  are  very 
minute,  or  where  the  groundmass  is  nearly  opaque  with  iron  oxide,  as  in 
many  scoriaceous  forms  of  basalt,  it  is  not  possible  to  recognize  orthoclase, 
and  the  exact  character  of  the  rock  is  uncertain  unless  its  geological  con- 
tinuity with  coarser-grained  forms  or  its  chemical  composition  be  known. 
A  number  of  basaltic  rocks  collected  from  the  Yellowstone  Park  belong 
in  this  category.  Some  are  seen  to  contain  very  little  orthoclase  (1137, 
1143,  1150,  1304,  1353).  In  others  the  presence  of  orthoclase  is  questiona- 
ble (1145,  1303,  1459,  1460,  1470,  1471,  1526,  1697,  1703).  Others  have 
groundmasses  that  are  but  slightly  crystallized.  Coarse-grained  equivalents 
of  these  transitional  varieties  occur  in  the  granular  core  as  orthoclase- 
gabbros. 

Transitional  varieties  between  shoshonite  and  highl)^  feldspathic  forms 
closely  related  to  banakite  occur  as  dikes  in  the  breccia  near  the  head  of 
the  canyon  of  the  Stinkingwater  River  (1468,  1455).  One  is  &  gray,  fine- 
grained rock,  resembling  diorite  in  outward  appearance.  It  consists  of 
cloudy  feldspars,  Avhich  are  mostly  allotriomorphic  orthoclase  with  partly 
altered  kernels  of  plagioclase  whose  exact  character  is  not  determinable, 
besides  small  crystals  of  labradorite  and  a  small  amount  of  an  allotrio- 
morphic, isotropic  mineral  which  is  also  clouded.  With  these  is  a  considera- 
ble amount  of  augite,  biotite,  and  magnetite,  and  fewer  serpentinized 
olivines.     The  augite  is  idiomorphic  in  part.     The  other  rock,  which  might 


BANAKITE. 


347 


vei-y  well  be  a  coarser-grained  portion  of  the  one  just  described,  is  whiter 
in  color  and  coarser  grained,  and  is  full  of  irregularly  shaped  tablets  of 
biotite,  from  1  to  3  nun.  broad.  It  has  the  same  mineral  composition  as  the 
first  one,  except  that  biotite  is  more  abundant,  and  some  of  the  feldspars 
ai'e  2  mm.  long. 

BAXAKITE. 

The  most  feldspathic  rocks  of  this  series,  which  occur  as  dikes  asso- 
ciated with  dikes  of  shoshonite  and  absarokite,  are  not  so  numerous.  A 
larger  proportion  of  them,  however,  have  been  analyzed.  They  occur  in 
Crandall  Basin,  in  Ishawooa  Canyon,  and  near  the  head  of  Stinkingwater 
River.  A  leucite-bearing  variety  forms  a  lava  sheet  near  Beaverdam  Creek. 
Their  chemical  composition  is  shown  by  the  analyses  in  the  accompanying 

table: 

Analyses  of  banakite  and  quurtz-hanalcite. 


Constituent. 

1 

2 

3 

t 

5a 

56 

6 

7 

SiO' 

51.82 

.71 

16.75 

4.56 

3.36 

.23 

52.63 

.81 

16.87 

4.52 

3.11 

.10 

51.46 

.83 

18.32 

4.61 

2.71 

.17 

52.33 

.71 

18.70 

4.95 

1.83 

.03 

.14 

52.93 

.72 

19.67 

3.07 

3.50 

.15 

51.56 

.65 

21.00 

5.17 

2.76 

Trace. 

57.29 

.72 

18.45 

4.38 

1.20 

Trace. 

.12 

60.89 
.49 

17.14 

3.32 

.95 

.09 

.19 

'PiO, 

AUG, 

Fe.O., 

FeO        

MnO     

NiO 

BaO 

.26 
4.03 
4.94 
.3.91 
5.02 

.29 
3.69 

4.77 
3.86 
5.17 

.21 
2.88 
4.69 
4.20 
4.75 

MgO 

2.91 
6.03 
4.11 
4.48 

2.69 
4.71 
4.51 
5.45 

2.52 

4.83 

4.37 

4.13 

.13 

.69 

.21 

2.27 

2.08 
3.57 
4.43 
5.43 

1.16 
3.58 
4.54 
5.71 

CaO 

NaiO 

K2O 

Li,0 , 

P.jOs 

.52 

.63 

.86 

.81 

.59 

.46 

.27 

SO3 

HiO 

3.97 

3.65 

3.89 

3.45 

2.73 

2.18 

1.61 

Total 

100.  08 

100. 10 

100. 38 

100. 31 

100. 09 

100. 29 

100.  31 

99.94 

1.  Banakite,  dike,  Lead  of  Lamar  River.     Analyst,  L.  G.  Eakins.     (1309.) 

2.  Banakite,  dike,  Hoodoo  Mountain.     Analyst,  L.  G.  Eakins.     (1296.) 

3.  Banakite,  dike,  Isliawooa  Canyon.     Analyst,  L.  G.  Eakins.     (1699.) 

4.  Banakite,  dike,  near  he.id  of  Stinkingwater  River.     Analyst,  W.  H.  Melville.     (1466.) 

5a.  Leucite-banakite,  lava  sbeet,  southeast  fork  of  Beaverdam  Creek.     Analyst,  L.  G.  Eakins. 


(1643.) 


56.  Leucite-banakite,  lava  sheet,  southeast  fork  of  Beaverdam  Creek.     Analyst,  J.  E.  Whitfield. 


(1643.) 


6.  Quartz-banakite,  dike,  near  head  of  Stinkingwater  River.     Analyst,  W.  H.  Melville.     (1463.) 

7.  Quartz-banakite,  dike,  near  head  of  stinkingwater  River.     Analyst,  W.  H.  Melville.     (1469.) 


348  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAX,  PARK. 

The  rocks  of  analyses  1  and  2  form  dikes,  the  second  one  occurring 
on  the  south  face  of  Hoodoo  Mountain  and  the  first  one  on  the  divide  south, 
the  two  dikes  trending  iii  the  same  direction,  a  little  east  of  south.  The 
rock  is  the  same  in  both  (1296,  1309).  It  is  light  gray  and  aphanitic,  with 
a  glistening  luster.  There  are  prominent  phenocrysts  of  black  augite  and 
rusted  spots  of  serpentinized  olivine,  but  no  porphyritical  feldspar.  In  the 
rock  from  Hoodoo  Mountain  (1296)  there  are  numerous  amygdules  of  white 
stellate  zeolite. 

In  thin  section  the  rocks  are  holocrystalliue,  with  more  feldspar  than 
ferromagnesian  minerals.  The  feldspar  is  lath-shaped  and  tabular,  with 
irregular  outlines.  The  crystals  are  simple  twins  with  low  extinction 
angles,  and  are  orthoclase  with  kernels  of  plagioclase,  which  is  mostly 
altered,  the  centers  of  the  crystals  being  decomposed  in  many  cases. 
There  is  considerable  serpentine  scattered  through  the  rock.  The 
ferromagnesian  minerals  of  the  groundmass  have  the  same  characters  as  in 
the  allied  rocks;  they  are  augite  and  biotite,  with  magnetite,  and  some 
ilmenite  in  rod-like  shapes;  apatite  occurs  in  needles.  The  rocks  contain 
much  analcite,  forming  clusters  of  crystals,  which  are  partly  cloudy  but 
mostly  transparent.  They  frequently  fill  cavities,  and  sometimes  occupy 
spaces  whose  outlines  appear  to  have  belonged  primarily  to  isometric 
minerals,  while  in  places  the  irregular  outline  and  inclosure  of  other  minerals 
make  it  appear  to  be  a  part  of  the  original  groundmass  of  the  rock.  It  is  to 
be  remarked  in  this  connection  that  basalts  with  abundant  crystals  of  analcite 
which  appear  to  be  primary  minerals  have  been  found  and  described  by 
Lindgren^  in  the  Highwood  Mountains,  about  200  miles  north  of  this  district. 
The  dike  on  the  divide  south  of  Hoodoo  Mountain  is  parallel  to  that  of  the 
absarokite  (1306)  whose  chemical  composition  is  shown  in  analysis  2  of  the 
table  on  p.  329. 

A  rock  from  the  ridge  west  of  Rocky  Creek  (1624)  is  almost  identical 
with  that  just  described.  The  groundmass  is  nearly  panidiomorphic.  The 
orthoclase  is  pronounced,  and  there  is  much  biotite  and  augite,  besides 
grains  of  an  isotropic  mineral,  probably  analcite.  Its  microstructure  is 
shown  in  PI.  XXXVIII,  fig.  1. 

Others  of  the  same  kind  are  from  Hoodoo  Basin  (1302),  from  the  south 

' Tenth  Census,  Vol.  XV,  1886,  p.  727 ;  also  Proc.  California  Acad.  Set.,  2d  ser.,  Vol.  Ill,  p.  51. 


BANAKITE.  349 

side  of  the  amiiliitheater  at  the  head  of  Stinkingwater  River  (1460),  and 
from  a  dike  on  the  Ishawooa  (1702). 

The  rock  of  the  third  analysis  (1699)  is  similar  to  the  last,  but  is 
more  feldspathic.  It  fonns  a  dike  in  the  Ishawooa  Canyon.  It  is  dark 
gray  and  waxj^  looking,  with  tabular  plienocrysts  of  feldspar,  and  many 
smaller  ones.  In  thin  section  it  is  holocrystalline,  with  abundant  lath-shaped 
twins  of  orthoclase,  having  a  rectangular  central  inclusion  of  labradorite 
(Ana  Aba).  Tliere  is  an  isotropic  cement  between  the  feldspars,  which  in 
places  is  cloudy,  and  niay  be  analcite  or  sodalite.  Biotite  and  augite  are 
abundant  in  small  crystals,  besides  magnetite  and  a  little  serpentine,  which 
appears  to  have  been  derived  from  small  olivines.  The  phenocrysts  are 
labradonte  (Auj  Aba),  some  of  which  have  borders  of  orthoclase.  There  is 
also  a  large  individual  of  isoti'opic  mineral  without  crystallographic  bound- 
ary.    This  rock  is  shown  in  PI.  XXXVIII,  fig.  2. 

A  closely  related  rock  (1466)  from  a  dike  near  the  head  of  Stinking- 
water  River  has  almost  the  same  chemical  composition  (analysis  4).  It 
carries  more  phenocrysts  of  serpentinized  olivine.  In  thin  section  it  is 
coarser  grained  than  the  last  variety,  and  the  feldspars  are '  more  altered 
and  less  distinct.  The  muieral  composition  is  like  that  of  the  rock  just 
described,  but  a  few  of  the  augites  are  bright  green,  indicating  an  approach 
to  segirite-augite. 

Analyses  ba  and  56  of  the  table  on  page  347  ai-e  of  a  leucite-bearing 
variety  (1643),  previously  alluded  to  as  forming  a  massive  surficial  sheet 
of  lava  immediately  overlying  tlie  shoshonite  which  occurs  on  the  south- 
east fork  of  Beaverdam  Creek,  and  whose  chemical  composition  is  given  in 
analysis  2  of  the  table  on  page  340.  Its  chemical  composition  is  but 
slightly  different  fi"om  that  of  the  rock  last  described  (1466),  analysis  4. 
The  rock  is  dark  gray,  with  a  somewhat  waxy  luster,  and  carries  small 
phenocrysts  of  feldspar,  serpentinized  olivine,  and  a  few  augites.  In  thin 
section  it  is  holocrystalline,  and  has  a  groundmass  of  mici'oscopic  leucites 
and  unstriated  feldspars,  which  appear  to  be  orthoclase,  but  may  be  plagio- 
clase  with  low  angles  of  extinction,  besides  augite  and  magnetite  and  some 
serpentine.  There  are  a  few  patches  of  light-brown  mica.  The  pheno- 
crysts are  labradorite,  serpentinized  olivine,  and  fewer  augites,  magnetites, 
and  stout  apatites.  The  crystals  of  leucite  h^ve  the  characteristic  forna  and 
inclusions,  and  in  places  are  somewhat  altered. 


350  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

This  rock  grades  into  denser,  finer-grained,  forms  (1601),  and  also  into 
vesienlar  forms  (1645,  1646),  which  are  purplish  gray  and  somewhat 
decomposed.  In  these  varieties  the  groundmass  is  finer  grained  and  the 
leucites  are  more  obscm-e,  being  filled  with  a  cloud  of  minute  dots  with 
only  a  narrow  margin  of  pure  substance  around  them.  The  remainder  of 
the  groundmass  consists  of  microlites  of  feldspar,  augite,  and  magnetite, 
with  some  serpentine.  Phenocrysts  are  few  and  are  labradorite,  serpen- 
tinized  olivine,  and  magnetite.  Leucite  is  abundant,  and  the  greater  part 
of  the  groundmass  appears  isotropic  between  crossed  nicols. 

The  rocks  of  analyses  6  and  7  belong  to  this  series  both  mineralogic- 
ally  and  chemically,  but  are  somewhat  more  siliceous,  having  5  to  9  per 
cent  more  silica.  They  might  properly  be  given  specific  names,  but  at 
present  we  prefer  to  class  them  with  banakite,  under  the  name  quartz- 
banakite,  although  the  amount  of  quartz  is  very  small.  The  two  rocks 
analyzed  are  closely  alike  in  alkalies  and  lime,  but  the  first  is  lower  in  silica 
and  slightly  higher  in  alumina,  iron  oxide,  and  magnesia.  They  differ 
somewhat  in  mineral  composition,  though  both  are  characterized  by  abun- 
dant feldspar  and  biotite.  The  first  one  (1463)  is  a  gray  rock,  distinctly 
crystalline,  with  a  few  megascopic  crystals  of  feldspar  and  mica.  In  thin 
section  it  is  seen  to  be  holocrystalline,  and  is  composed  of  lath-shaped, 
rectangular,  and  allotriomorphic  feldspars,  with  considerable  brown  biotite, 
in  part  idiomorphic,  besides  magnetite  and  a  little  augite,  partly  decom- 
posed. There  is  very  little  quartz  and  calcite.  The  central  part  of  the 
feldspar  crystals  is  lime-soda  feldspar,  in  some  cases  labradorite,  judging 
from  the  optical  properties.  The  marginal  part  is  orthoclase,  which 
forms  a  considerable  portion  of  the  feldspar,  but  is  subordinate  to  the 
plagioclase. 

The  second  one  (1469)  is  a  light-gray  rock  with  numerous  small  tabu- 
lar feldspars  and  some  large  ones,  and  few  phenocrysts  of  biotite.  Most  of 
the  megascopic  feldspars  exhibit  polysynthetic  twinning,  but  a  few  appear 
to  have  the  brilliant  unbroken  cleavage  of  sanidine.  None  of  these,  how- 
ever, are  found  in  the  thin  sections  prepared,  in  which  all  the  feldspar 
phenocrysts  are  polysynthetic  twins.  In  thin  section  the  rock  is  seen  to  be 
holocrystalline  and  nearly  panidiomorphic,  the  feldspar  of  the  groundmass 
being  in  small  rectangular  to  lath-shaped  crystals  with  fluidal  arrangement 
(PI.  XXXVIII,  fig.   3).     The  rock  also  contains  a  comparatively  small 


U.  S.  GEOLOG(CAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.    XXXVIII 


fAj  «  25 


rBj  X   28 


rci  X  30 


(-  flj  X  42 


PHOTOMICROGRAPHS    OF   BANAKITE,    QUARTZ-BANAKITE,    AND    ANDESITE 


THE  MELIOTVPE  PfilNTIHG  CO.,  BOSTON 


ROCKS  RESEMBLING  AHSAROKITE.  351 

ajnount  of  biotite,  very  little  ma<>'notite  i\i\(\  aug-itejand  some  colorless  apatite. 
The  t'eldspar  plienocrysts  are  labradorite,  while  the  feldspar  of  the  ground- 
mass  is  mainly  orthoclase,  with  kernels  of  fresh  feldspar  that  has  the  optical 
characters  of  oligoclase.  There  is  very  little  quartz,  and  some  little  chlorite 
or  serpentine.  The  feldspars  of  this  rock  are  quite  fresh,  as  are  also  the 
biotites.  A  coarser-grained  and  more  altered  modification  of  this  rock 
occurs  in  another  dike  near  the  head  of  the  main  stream  (1467).  The 
feldsjiars  of  the  groimdmass  are  not  idiomorphic,  but  acicular,  with  the 
microstructure  characteristic  of  syenite-porphyries.  The  mineralogical 
analogy  between  banakite  and  shoshonite  is  chiefly  in  the  association  of 
labradorite  phenocrysts  with  orthoclase  microlites.  Biotite  and  augite  are 
common  to  some  varieties  of  both,  while  olivine  is  present  in  one  variety 
of  banakite  and  is  connnon  to  most  shoshonites.  These  rocks  are  the 
highly  feldspathic  modification  of  shoshonite  magma,  and  are  complemen- 
tary to  absarokite,  which  rejjresents  the  least  feldspathic  modification  of  the 


same  magma. 


SIMILAR  KOCKS  IN  MONTANA. 


Rocks  almost  identical  with  absarokite  occur  in  the  region  about  Boze- 
man,  Montana,  and  have  been  thoroughly  described  by  MerrilP  in  a 
bulletin  of  the  United  States  National  Museum.  They  are  intrusive 
bodies  in  part,  and  have  been  described  under  the  head  of  questionable 
basalt  and  lampi*ophyre.  They  are  more  or  less  decomposed  in  some 
cases  and  quite  fresh  in  others.  Their  mineral  composition  and  habit  are 
like  those  of  the  rocks  here  called  absarokite.  The  phenocrysts  are  olivine 
and  monoclinic  pyroxene,  whose  chemical  composition  in  the  case  of  the 
rock  from  near  Fort  Ellis  is  that  of  chrome-diopside.  The  rock  itself  is 
imusually  rich  in  magnesia  and  comparatively  low  in  iron  oxide,  so  that  it 
is  probable  that  the  monoclinic  pyroxenes  in  the  other  absarokites  are  not 
such  pure  diopsides,  but  are  most  likely  malacolites  or  augites.  The  pyrox- 
ene in  the  coarse-grained  shonkinite  of  Square  Butte,  Montana,  which  is 
related  to  absarokite  chemically,  has  been  shown  by  Weed  and  Pirsson  to 
be  augite.  There  are  no  phenocrysts  of  feldspar,  and  the  groundmass  con- 
tains orthoclase,  or  when  not  distinctly  crystallized  is  found  to  be  compara- 
tively rich  in  potash  and  soda.     The  chemical  compositions  of  the  rocks 

'  Merrill,  Geo.  P.,  Notes  on  some  eruptive  rocks  from  Gallatin,  Jeflferson,  and  Madison  counties, 
Montana:  Proc.  U.  S.  Nat.  Mus.,  Vol.  XVII  (No.  1031),  1895,  pp.  637-673. 


352 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 


described  by  Merrill  are  shown  in  the  first  four  analyses  in  the  table, 
which  is  introduced  here  for  comparison  with  those  of  absarokite  in  the 
Yellowstone  Park. 

Analyses  of  absarokite  and  similar  rocks. 


Constitaent. 

1 

2 

3 

4 

5 

6 

7 

SiO.2 

46.90 

.41 

10.17 

.33 

1.22 

5.17 

.10 

20.98 

6.20 

1.16 

2.04 

.44 

49.13 

.42 

9.05 

.39 

3.57 

5.05 

.15 

17.21 

5.68 

2.01 

2.24 

.38 

.05 

50.82 

.59 

11.44 

.03 

.25 

8.94 

.19 

14.01 

8.14 

1.79 

3.45 

.20 

.06 

51.65 

.55 

13.89 

.80 

2.70 

4.80 

.15 

11.56 

4.07 

2.99 

4.15 

.21 

.19 

.19 

1.30 

1.89 

50.03 

.61 

14.08 

Trace. 

2.92 

6.11 

.08 

10.73 

7.46 

1.46 

2.64 

.42 

.04 

52.33 

.14 

15.09 

54.15 

Not  det. 

18.92 

TiO.2 

AI.O3 

'Cr.iOs 

FeiO  1 

4.31 
4.03 

.09 
6.73 
7.06 
3.14 
3.76 
1.02 

.07 

1      6.79 

Not  <let. 
1.90 
3.72 
5.47 
8.44 

Not  (let. 
CI.  42 

FeO 

MnO           

MeO        

CaO.-     ..         

Na,0 

K2O 

P.Os 

BaO  

SO3 

HjOat  100° 

1.04 
4.38 

.84 
3.50 

.58 

3.70 

2.68 

Not  det. 

Total 

100. 54 

99.67 

100. 49 

101.09 

100.  28 

100.  45 

99.81 

1.  Fort  Ellis,  2J  miles  southeast  of  Bozeman,  Montana.     Analyzed  by  T.  M.  Chatard. 

2.  Bear  Creek,  Madison  Valley,  Montana.     Analyzed  by  T.  M.  Chatard. 

3.  South  Bowlder  ,aud  Antelope  Creek,  Montana.     Analyzed  by  L.  G.  Eakins. 

4.  Cottonwood  Creek,  Montana.     Analyzed  by  T.  M.  Chatard. 

5.  Cottonwood  Creek,  Montana.     Analyzed  by  L.  G.  Eakins. 

6.  Cottonwood  Creek,  Montana.     Analyzed  by  L.  G.  Eakins. 

7.  Cottonwood  Creek,  Montana.     Analyzed  by  G.  P.  Merrill. 

The  variability  of  these  rocks  within  certain  limits  is  evident,  the 
greatest  range  being  in  magnesia.  While  not  exactly  alike  chemically, 
they  agree  in  being  low  in  silica  and  alumina,  high  in  magnesia,  compara- 
tively high  in  alkalies,  with  high  potash.  The  rock  from  which  the  fifth 
analysis  was  made  is  a  transitional  variety  between  absarokite  and  the 
normal  basalt  of  the  region. 

The  sixth  analysis  is  from  an  intrusive  rock  called  augite-porphyrite 
by  Merrill.  It  corresponds  to  shoshonite  in  alkalies,  but  is  lower  in  alumina 
and  higher  in  magnesia  and  lime.  It  is  intermediate  between  shoshonite 
and  absarokite.  It  is  associated  with  the  rocks  whose  chemical  composition 
is  given  by  analyses  4  and  5,  and  plainly  belongs  to  this  series. 


KOGKS  (JORKKSPONDING  TO  ABSAUOKITE  AND  BANAKITE.      353 

Near  tlic  absarokite  of  Cottonwood  Creek  is  a  syoiiitic  rock  wliicli 
rorrespoiuls  in  sonic  respects  to  the  l)anakite  of  the  Stinkingwater  region, 
in  that  it  is  highl}-  feldsj^atliic  with  abnndant  biotite  and  some  pyroxene. 
Its  niicrostructure  is  that  of  trachyte-porphyry.  Chemically  (analysis  7) 
it  is  much  richer  in  alkalies,  liaving  8.44  per  cent  of  j)otasli  and  5.47 
per  cent  of  soda,  and,  as  Merrill  points  out,  is  (piite  like  the  sodalite- 
syenite  of  Square  Butte,  Montana,  described  l)y  Lindgren.'  They  are 
more  alkaline  feldspathic  nioditications  of  magmas  which  have  yielded 
absarokite  and  the  somewhat  similar  magma  which  at  Square  Butte  has 
crystallized  into  the  coarse-grained  rock  called  shonkinite.^ 

This  new  type  of  granular  crystalline  i-ock  consists  essentially  of  augite 
and  orthoclase,  with  biotite,  olivine,  magnetite,  albite,  and  anorthoclase, 
with  accessory  nepheline  and  sodalite,  and  other  minerals.  Its  chemical 
composition,  as  shown  in  the  accompanying  analysis,  is  similar  to  that  of 
the  absarokites  of  the  Yellowstone  Park,  except  in  the  higher  percentage 
of  lime,  but  the  low  silica  and  alumina  and  the  relatively  high  alkalies, 
with  high  potash  and  high  magnesia  and  lime,  .show  its  chemical  relation 
to  this  group. 

In  the  Little  Belt  Jlountains  of  Montana'  there  are  rocks  almost  the 
same  as  absarokite  chemically,  but  coarsely  crystalline,  as  at  Square  Butte. 
And  Weed  and  Pirsson  have  desci-ibed  the  petrographical  characters  of  the 
rocks  from  Yogo  Peak,  whose  chemical  composition,  together  with  that  of 
the  rock's  from  Square  Butte,  Highwood  Mountains,  is  shown  by  the  analyses 
in  the  table  on  the  following  page. 

'Liudgren,  W.,  Eruptive  rocks  from  Montana :  Proc.  California  Acad.  Nat.  Sci.,  2d  series,  Vol. 
Ill  (Part  I,  1891),  1893,  pp.  45-47. 

'•'Weed,  W.  H.,  and  Pirsdon,  L.  V.,  Highwood  Mountains  of  Montana:  Bull.  Geol.  Soc.  America, 
Vol.  VI,  pp.  389-422,  pis.  24-26. 

'Weed,  W.  H.,  and  Pirsson,  L.  V.,  Igneous  rocks  of  the  Yogo  Peak,  Montana:  Am.  Jour.  Sci., 
3d  series,  Vol.  L  (No.  300,  Dec,  1895),  pp.  467-479. 
ilON  XXXII,  FT  II 23 


354  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Analyses  of  igneous  rocks  from  Yogo  Peak  and  Square  Butte,  Montana. 


Constituent. 

1 

2 

' 

i 

5 

SiO..                       

61.65 

.56 

15.07 

2.03 

2.25 

.09 

3.67 

4.61 

.27 

4.35 

4.50 

.33' 

Trace. 

.10 

Trace. 

54.42 

.80 

14.28 

3.32 

4.13 

.10 

6.12 

7.72 

.32 

3.44 

4.22 

.59 

Trace. 

.13 

Trace. 

48.98 

1.44 

12.29 

2.88 

5.77 

.08 

9.19 

9.65 

.43 

2.  22 

4.96 

.98 

Trace. 

.08 

Trace. 

.22 

.26 

.56 

46.73 

.78 

10.05 

3.53 

8.20 

.28 

9.68 

13.22 

56.45 

.29 

20.08 

1.31 

4.39 

.09 

.63 

2.14 

TiO. 

ALOi        

Fe.O, 

FeO       

MnO 

MgO 

CaO 

BaO 

Na,0 

1.81 
3.76 
1.51 

5.61 

7.13 

.13 

K:0 

P  O, 

Cr.O:, 

SrO 

LijO 

.     Trace. 

CI      .18 

]         1. 24 

Fl 

.43 

1.77 

H,0  at  110° 

.26 

.41 

.22 
.38 

H2O  above  110- 

Total 

100. 15 

100. 19 

99.99 
0=F1  .08 

100.  97 
0=C1  .04 

100. 45 
.10 

99.91 

100.  93 

100.  35 

1.  Syeuite,  Yogo  Peak.     Analyzed  by  W.  F.  Hillebrand. 

2.  Monzouite,  Yogo  Peak.     Analyzed  by  W.  F.  Hillebrand. 

3.  Shonkinite,  Yogo  Peak.     Analyzed  by  W.  F.  Hillebrand. 

4.  Shonkinite,  Square  Butte.     Analyzed  by  L.  V.  Pirsson. 

5.  Sodalite-syeuite,  Square  Butte.     Analyzed  by  AV.  H.  Melville. 

These  authors  state  that  the  three  rocks  from  Yogo  Peak  grade  into 
oue  another,  and  are  facies  of  one  mass,  whose  variations  are  the  result  of 
differentiation.  They  are  granular  crystalline,  and  consist  essentially  of 
orthoclase  and  augite  in  different  proportions,  with  subordinate  amounts 
of  plagioclase,  biotite,  magnetite,  and  in  the  syenite,  hornblende,  and  in 
shonkinite,  olivine,  besides  accessory  minerals.  In  the  syenite  orthoclase 
exceeds  auo-ite,  in  monzonite^  orthoclase  equals  augite,  and  in  shonkinite 
auo-ite  exceeds  orthoclase.  Chemically  the  series  from  Yogo  Peak  is 
characterized  by  comparatively  low  alumina,  with  relatively  high  potash, 

1  The  rock  called  yogoite  in  the  i^aper  cited  has  been  shown  by  these  authors  in  a  subsequent 
paper  to  be  the  same  as  Brogger's  monzouite,  and  the  name  yogoite  has  been  withdrawn.  See  The 
Bear  Paw  Mountains  of  Montana :  Am.  Jour.  Sci.,  4th  series,  Vol.  1, 1896,  pp.  351-362. 


COMl'LEMENTAUY  HOCKS.  355 

which  is  nearly  constant.  Tlie  sum  of  the  alkalies  decreases  with  decrease 
of  silica  and  alumina.  Ma<>nesia  and  lime  are  fairly  liij^h.  In  the  two 
rocks  of  S(iuare  Butte  the  shonkinite  is  like  that  of  Yoyo  I'eak,  but  alumina 
and  alkalies  are  somewhat  lower,  and  mag-nesia  and  lime  hii)-lier.  The 
syenite  of  Square  Butte,  the  complementary  rock  of  shonkinite,  is  high  in 
alumina  and  alkalies  and  very  low  in  magnesia  and  lime,  with  very  high 
potash.  In  these  two  cases  we  find  shoukinites  as  extreme  forms  of  differ- 
entiations in  connection  with  syenitic  rocks  quite  different  from  one  another 
in  chemical  composition,  one  being  comparatively  low  in  alumina  and  the 
other  high,  the  sum  of  the  alkalies  in  one  case  being  8.85  per  cent  and  in 
the  other  12.74  per  cent.  In  each  instance  the  associated  rocks  are  facies 
of  one  igneous  mass.  A  comj^arison  of  the  series  of  differentiation  products 
just  described  shows  to  what  extent  they  may  differ  from  one  another  in 
neighboring  regions. 


CHAPTER  X. 
THE    RHYOLITES. 


By  Joseph  Paxson  Iddings. 


INTRODUCTIOIf. 

The  rhyolite  (if  the  Yellowstone  National  Park  occurs  almost  whollj'- 
as  extrusive  surficial  lava  flows  in  the  form  of  nearly  horizontal  sheets, 
some  having  enormous  proportions.  In  only  one  locality  does  it  assume 
the  character  of  a  volcanic  mountain,  in  which  place  it  occurs  as  breccia  and 
also  as  intrusions  and  surface  flows.  It  constitutes  the  great  plateau  of  the 
Park,  and  sends  out  arms  into  valleys  in  the  surrounding  ranges  of  moun- 
tains, and  is  found  in  isolated  remnants  upon  their  slopes.  Owing  to  its 
great  areal  extent,  and  also  to  the  fact  that  it  is  in  places  more  than  2,000 
feet  thick,  its  volume  is  very  large.  It  is  exposed  to  view  in  many  clifl"s 
and  bare  slopes  tlu'oughout  the  region,  and  has  been  studied  in  detail  in 
many  places. 

Its  two  most  striking  petrological  characteristics  are  the  uniformity  of 
its  composition  chemically  and  mineralogically  and  the  multiformity  of  its 
physical  aspect.  With  a  range  of  only  5  per  cent  in  the  silica,  and  of  much 
less  in  the  other  constituents  throughout  miles  of  material,  there  is  the 
greatest  diversity  in  the  appearance  and  texture  of  the  rock,  even  within 
the  limits  of  a  few  feet.  Its  color  may  be  white,  black,  yellow,  red,  brown, 
or  grays  of  various  tones,  which  may  be  uniform  for  broad  areas,  or  mingled 
in  blotches,  streaks,  and  layers,  or  finely  speckled  in  small  spots.  Its 
luster  may  be  dull  and  stony  or  vitreous  and  brilliant,  and  its  texture  may 
be  rough  or  smooth  as  the  rock  is  porous,  vesicular,  and  pumiceous,  or 
dense  and  compact.  In  some  localities  the  characters  are  quite  uniform  for 
a  large  extent  of  rock;  in  others  they  are  highly  diversified.  In  order  to 
convey  a  proper  idea  of  the  relations  of  these  various  modifications  to  one 

356 


t> 


KHYOLITE  NEAR  JIAMMOTII  HOT  SPKINGS.  357 

another  and  to  show  their  orij^iu,  it  will  he  necessary  to  descrihe  the  field 
occurrence  and  niegascopicul  characteristics  in  a  number  of  localities  within 
the  Park,  and  afterwards  to  treat  systematically  the  microscopical  characters. 

MEGASCOPICAIi  CHAllACTERS. 

VICINITY  OF    MAMMOTH    HOT  SPRINGS. 

The  rhyolite  at  the  Golden  Gate,  where  the  road  to  the  Geyser  Basins 
passes  alonjf  the  face  of  a  rocky  cliff  at  the  south  end  of  Terrace  Mountain, 
is  a  dense,  light  purplish-gray  rock,  separated  into  distinct  horizontal 
layers,  and  jointed  by  irregular  vertical  cracks,  which  cause  it  to  weather 
in  pinnacles  of  angular  blocks.  In  the  lower  part  of  the  cliff  the  rhyolite 
is  dense  and  dark  purple,  passing  up  into  lighter-colored  and  more  porous 
fonns,  with  occasional  flattened  ca\'ities  and  yellow  spots.  The  rock  has  a 
stony  lithoidal  groundmass,  in  which  glisten  small  crystals  of  quartz  and 
sanidine  (1775,  1776). 

It  also  forms  a  prominent  cliff,  100  to  150  feet  high,  along  the  top  of 
the  southern  portion  of  the  west  escarpment  of  Mount  Everts,  which  is 
well  shown  in  the  panoramic  view  of  this  mountain,  by  W.  H.  Holmes, 
wliich  accompanies  his  report  on  the  geology  of  the  Yellowstone  National 
Park.i  I 

Here  the  rhyolite  is  massive,  with  a  rude  columnar  structure.  It  is 
reddish  purple  and  lithoidal,  with  many  small  jihenocrysts  of  quartz  and 
feldspar.  Near  the  northern  end  of  the  sheet,  on  the  summit  of  Mount 
Everts,  it  passes  into  a  grayish-white  rock,  finely  porous  in  spots  (1762). 
Beneath  the  rhyolite  sheet  there  is  a  deposit  of  1-hyolitic  dust  or  ash 
about  4  feet  thick,  in  places  more,  which,  as  Holmes  has  pointed  out,  is 
beautifully  and  delicately  laminated  in  light  and  dark  grays,  brown,  and 
bufts.  The  top  of  the  sandstone  strata  on  which  this  ash  rests  is  covered 
with  a  thin  layer  of  small  fragments  of  the  same  kind  of  sandstone  and 
sandy  soil,  only  a  few  inches  thick.  Ujjon  this  is  a  layer  of  rhyolitic  ash 
or  sand,  passing  up  into  very  fine  white  dust  (1763),  formed  of  microscopic 
angular  particles  of  glass  and  a  small  amount  of  crystalline  grains.  This  is 
thinly  laminated.  Over  it  are  alternating  layers  of  coarser  rhyolitic  sand 
and  finer  dust,  all  laminated,  with  the  thinnest  possible  lines,  wliich  are 


'Twelfth  Aun.  Rept.  U.  S.  Geol.  and  Geog.  Stiiv.  Terr.  (Hayden),  for  1878;  Part  II,  PI.  XXXII. 


358     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

persistent  and  perfectly  parallel  to  one  another  and  to  the  plane  of  contact 
of  the  overlying-  massive  rhyolite.  This  friable  portion  passes  npward  by 
insensible  gradations  into  dark-purple  dense  rock  with  abundant  pheno- 
crysts,  almost  indistinguishable  from  the  overlying  rock,  from  which, 
however,  it  is  separated  by  a  thin  layer  of  black  perlitic  glass  (1769)  less 
than  one-fourth  of  an  incli  thick.  A  similar  deposit  of  dust  iniderlies  the 
rhyolitic  sheet  in  the  mountain  north  of  TeiTace  Mountain,  where  it  has 
been  indurated  in  the  same  manner. 

The  rhyolite  sheet  of  j\Iount  Everts  extends  over  the  whole  southern 
half  of  the  top  of  the  mountain  and  down  the  slopes  of  the  southeastern 
spurs  to  the  valley,  and  overlies  a  thin  sheet  of  vesicular  basalt  which  is 
exposed  in  a  number  of  places.  It  is  found  near  the  top  of  the  plateau  wall 
south  of  Lava  Creek,  where  it  is  about  150  feet  thick,  and  extends  south 
into  the  gi'eat  plateau.  In  the  neighborliood  of  Osprey  Falls,  east  of 
Bunsen  Peak,  the  same  rhyolite  sheet  is  exposed  in  the  cliff  near  the  falls. 
Beneath  it  is  a  deposit  of  light-gray  rhyolitic  dust,  which  grades  upwai'd 
into  more  compact  rock  and  tlien  into  dark  glassy  rock  immediately  beneath 
the  massive  rhyolite.  The  rhyolite  sheet  is  from  100  to  150  feet  thick  and 
overlies  8  sheets  of  basalt,  which  are  superimposed  nearly  hoi'izontally, 
and  it  is  in  turn  overlain  by  a  50-foot  sheet  of  basalt,  the  whole  series, 
including  the  rhyolite,  being  finely  columnar.  The  surfaces  of  the  columns 
of  the  rhyolite  and  of  those  of  basalt  are  very  similar  in  color,  owing  to 
weathering  and  to  the  lichens,  so  that  the  two  rocks  are  scarcely  distin- 
guished from  one  another  at  a  distance,  the  rhyolite  appearing  as  dark  as 
the  Ijasalt.  Near  the  falls,  however,  the  rhyolite  columns  are  longer  and 
straighter,  and  become  granular  at  the  upper  ends,  where  they  weather  into 
pimiacles. 

The  rhyolite  forming  the  cliff  at  the  Golden  Gate  contiimes  as  a 
nearly  horizontal  sheet  northward  beneath  the  travertine  deposit  on  Ter- 
race Mountain,  and  forms  the  top  of  tlie  hill  north  of  this,  where  it  is  from  150 
to  200  feet  thick.  It  is  exposed  in  a  bold  cliff  heading  an  amphitheater  on 
the  northeast  side  of  this  mountain,  and  has  the  same  characters  as  in  the 
cliff  on  Blount  Everts.  It  is  dark  purple,  lithoidal,  and  full  of  rather  large 
phenocrysts.  In  the  top  of  the  cliff  it  is  in  places  glassy  and  perlitic,  and 
contains  large  vesicles.  Beneath  the  sheet,  as  already  mentioned,  there  is  a 
deposit  of  rhyolitic  dust,  whose  upper  portion  is  indurated  like  that  on 


OliSIDIAN  CLIFF.  35i) 

Jlount  Everts,  the  nuiteriiil  from  Ijotli  loealities  being'  identical.  The 
rhyohte  sheet  continues  north  luitil  it  rtiuches  the  an(U?sitic  breccia  forming 
the  southeast  spur  of  Sepulchre  Mountain,  upon  which  it  rests,  its  lower 
portion  inclosing  fragments  of  andesite.  It  extends  along  the  base  of 
the  south  slope  of  Sepulchre  Mountain  west  to  the  divide  between  Glen 
and  Reese  creeks,  and  forms  the  bench  of  dark-])urple  rock  with  small 
phenocrysts  south  of  Cache  Pond,  and  also  an  isolated  remnant  of  light- 
reddish  earthy  rhyolite  overlying  the  andesite  on  the  west  base  of  Sepulchre 
Mountain. 

From  this  we  see  that  in  the  neighborhood  of  the  Mammoth  Hot 
Springs  the  rhyolite  has  a  very  uniform  character,  being  mostly  lithoidal, 
except  in  one  place  on  the  old  Norris  road  northwest  of  Terrace  Mountain, 
where  a  small  mass  of  dark-coloi'ed  rhyolitic  perlite  is  exposed,  which,  as 
Holmes  has  remarked,  "is  similar  to  that  forming  the  under  surface  of 
most  of  the  rhyolitic  flows  in  this  region."  In  this  vicinity,  however,  the 
under  surface  of  most  of  the  rhyolite  sheet  has  only  a  thin  iilm  of  perlitic 
glass  along  its  contact  with  the  underlying  rhyolitic  tuff.  The  tuff  deposit 
has  not  been  observed  on  Glen  Creek,  nor  at  the  head  of  Reese  Creek, 
nor  does  it  underlie  the  most  northern  remnant  of  rhyolite  which  occurs  on 
the  west  side  of  Bear  Gulch,  north  of  the  Park  boiuidary. 

OBSIDIAN  CLIFF. 

The  rhyolite  which  forms  the  plateau  country  and  the  flat-topped 
bluffs,  300  or  400  feet  high,  on  both  sides  of  Willow  Park  along  Obsidian 
Creek  is  a  lithoidal  to  earthy  rock,  reddish  purple  in  darker  and  lighter 
shades,  and  filled  with  brilliant  phenocrysts  of  quartz  and  sanidine,  the 
latter  exhibiting  a  blue  iridescence  in  man)-  localities.  Rhyolite  of  the  same 
character  continues  to  form  the  plateau  as  fa^-  south  as  the  Norris  Geyser 
Basin,  being  well  exposed  all  along  the  road.  It  also  extends  east  to  Lava 
Creek  and  forms  the  west  base  of  the  mountains  west  of  Tower  Creek, 
overlying  andesitic  breccia  and  reaching  an  altitude  of  8,800  feet. 

At  the  noiihern  end  of  Beaver  Lake  the  lithoidal  rhyolite  is  overlain 
by  a  great  flow  of  rhyolitic  obsidian,  which  covers  the  high  country  to  the 
east  in  a  sheet  75  to  100  feet  thick  and  has  accumulated  in  an  ancient  valley 
to  the  depth  of  200  feet.     The  stream   erosion  of  this  thicker  mass  has 


360     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

formed  Obsidian  Cliff/  whose  shining  black  columns  of  g-lass  rise  100  feet 
above  the  road. 

The  cliff  stretches  for  half  a  mile  from  the  outlet  of  Beaver  Lake 
along  the  east  side  of  Obsidian  Creek,  being  150  to  200  feet  high  near  the 
lake  and  becoming  lower  northward.  The  upper  half  is  a  vertical  face  of 
rock,  the  base  of  which  is  obscured  by  debris  of  large  blocks  of  the  same 
material.  The  obsidian  sheet  extends  eastward  up  the  rude  benches  to  the 
top  of  the  plateau  400  feet  alcove  Beaver  Lake.  Along  the  west  edge  of 
this  table-land  it  forms  a  cliff'  about  50  feet  high,  which  extends  south  to 
the  Lake  of  the  Woods. 

Following  the  obsidian  back  from  the  face  of  this  upper  cliff,  over  the 
hummocky  surface  of  the  plateau,  the  black  glass  becomes  filled  with  gas 
cavities  and  passes  into  banded  ])umiceous  rock,  and  finally  into  light-gray 
pumice.  This  covers  the  surface  of  the  plateau  for  2^  miles  eastward,  to 
the  valley  of  Solfatara  C'reek.  Here  again  the  lava  flow  is  exposed  in  a 
cliff,  the  lower  portion  of  which  is  lilack  and  red  ob.sidian.  Toward  the 
south  the  obsidian  flow  extends  a  mile  beyond  the  Lake  of  the  Woods,  and 
northward  it  crosses  the  east-west  drainage  that  cuts  off  the  higher  jwrtion 
of  the  plateau  a  distance  of  some  5  miles.  The  original  thickness  of  this 
lava  flow  is  not  known,  since  the  upper  pumiceous  portion  has  been  eroded 
to  a  variable  extent.  The  denser  obsidian  portion  is  from  75  to  100  feet 
thick. 

The  point  at  which  the  obsidian  broke  through  the  older  rocks  has  not 
been  discovered,  but  it  is  evident  that  the  lava  forming  Obsidian  Cliff 
flowed  down  from  the  high  plateau  in  a  northwest  direction  into  a  preexist- 
ing valley.  The  planes  of  flow  in  the  lava  clearly  indicate  that  it  crept 
down  the  slope  back  of  Obsidian  Cliff  and  accumulated  in  the  bottom  of  a 
channel  between  rhyolite  hills. 

The  most  noticeable  feature  of  this  body  of  obsidian  is  its  columnar 
structure,  which  is  confined  to  the  southern  end  of  the  cliff.  It  is  shown 
in  PI.  XXXIX.  The  glassy  columns  rise  from  a  talus  slope  that  extends 
50  feet  up  the  cliff.  They  are  vertical  prisms  50  or  60  feet  high,  and  vary 
in  width  from  2  to  4  feet  near  the  south  end  of  the  cliff,  the  width  of  each 
column  being  quite  constant  throughout  its  length.     (Jn  the  south  face  of 

'Idding8,  J.  P.,  Obsidian  Cliff,  Yellowstone  National  Park:  Seventh  Ann.  Kept.  U.  S.  Geol. 
Survey,  1888,  pp.  249-295. 


U.    5.    GEOLOOrCAL  SURVFv 


MONOGRAPH  XXXII      PART  II      PL  XL 


TOP  OF   COLUMNS,   OBSIDIAN    CLIFFS. 


COLUMNAR  OBSIDIAN.  361 

this  end  of  the  cHff  the  columns  are  the  same,  but  grow  less  clearly  defined 
toward  the  oast,  where  a  sharp  bend  in  the  lava  sheet  has  fV)nned  gaps  in 
the  rock  and  has  destroyed  the  ciuitinuity  of  the  mass.  Beyond  this  tlie 
colunnis  incline  considerably  toward  the  west,  as  though  the  underlying 
surface  of  contact  sloped  toward  the  west  also.  The  columns  in  the  main 
face  of  the  cliff  are  tilted  If)"  to  the  eastward,  and  the  planes  of  flow  which 
cross  them  have  an  average  dip  of  10^  E.,  indicating  that  the  underlying 
surface  at  this  place  sloped  toward  the  east.  The  colunnis  become  broader 
to  the  north,  the  largest  being  20  feet  in  width,  and  with  the  change  in  the 
character  of  the  rock  from  glassy  to  lithoidal  they  grade  into  massive  blocks 
formed  by  vertical  cracks  farther  apart.  The  columns  have  four,  five,  and 
six  sides,  which  are  unequally  developed,  but  at  a  distance  the  general  effect 
is  quite  regular. 

The  obsidian  forming  the  lower  part  of  the  columns  is  dense  and  black, 
and  transparent  only  on  verj'  thin  edges.  It  is  traversed  by  bands  or 
layers  of  small  gray  spherulites.  In  this  part  of  the  columns  there  are 
almost  no  cavities  or  lithophysfe,  and  but  little  contortion  of  the  layers. 
Higher  up,  the  obsidian  is  less  massive  and  contains  large  lithophysEe 
flattened  parallel  to  the  plane  of  flow.  The  tops  of  the  columns  pass  into 
-obsidian,  which  for  10  feet  is  quite  dense,  but  above  this  is  full  of  large 
cavities  which  honeycomb  the  mass.  This  may  be  seen  in  the  photograph 
of  the  columns  (PL  XL).  This  upper  portion,  about  50  feet  thick,  is 
divided  by  vertical  cracks  into  broad  quadrangular  blocks.  The  sides  of 
the  columns  are  comparatively  straight,  and  are  independent  of  the  flow 
stiTicture  within  the  mass,  which  is  indicated  by  the  spherulitic  layers  that 
traverse  the  rock  in  parallel  planes  more  or  less  contorted  These  layers 
pass  through  the  columns  at  all  angles,  exhibiting  abrupt  folds  and  curves, 
which  have  been  cut  across  sharply  by  the  colunmar  cracks.  The  crystal- 
line spherulitic  layers  formed  planes  of  weakness,  along  which  transverse 
cracks  were  produced.  There  is  another  kind  of  pai-ting,  which  took  place 
while  the  lava  was  still  molten,  but  when  it  was  so  viscous  that  in  places 
where  vertical  layers  pulled  apart  in  flowing  down  the  slope  the  gaps  did 
not  close  up.     These  are  of  only  exceptional  occurrence. 

The  columnar  portion  of  the  west  face  of  the  cliff  extends  for  only  a 
few  hundred  feet  northward,  the  character  of  the  rock  also  changing  in  this 
direction.     The  spherulitic  and  lithoidal  layers  also  become  more  frequent, 


362  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

until  the  black  glass  appears  as  thin  bands  in  a  light-gray  rock,  and  finally 
the  whole  mass  is  a  laminated  lithoidal  rock.  The  lithoidal  form  of  the 
rock  is  not  found  in  the  thinner  portions  of  the  lava  flow,  but  only  where  it 
has  accumulated  in  the  ancient  channel.  It  is  split  into  thin  plates  along 
the  planes  of  flow,  owing  to  the  differences  in  texture  of  the  alternating 
layers,  which  vary  in  degree  of  crystallization.  This  delicate  lamination 
and  variability  of  crystallization  will  be  referred  to  again,  after  the  micro- 
scopical characters  have  been  described. 

Owing  to  the  fact  that  the  spherulitic  structure,  which  is  highly  devel- 
oped in  the  obsidian  at  this  place,  is  typical  of  that  which  occurs  in  a  great 
number  of  other  localities  in  the  Yellowstone  Park,  it  seems  advisable  to 
describe  it  in  considerable  detail,  in  order  to  give  a  clear  impression  of  this 
very  characteristic  mode  of  crystallization.  The  spherulites  form  isolated 
spherical  bodies  or  groups  of  spheres,  often  so  intimately  intergrown  as  to 
form  layers  in  the  rock.  Their  substance  is  lusterless  and  stony,  dull 
bluish  gray  and  pink.  They  are  of  various  sizes,  the  larger  ones  frequently 
being  hollow  or  porous. 

The  simplest  :form  of  the  megascopic  spherulites  is  that  of  small  dark- 
blue  spherules,  about  the  size  of  a  mustard  seed,  embedded  in  the  black 
obsidian.  When  broken,  they  appear  lighter  gray  within,  have  a  dense 
porcelain-like  texture,  and  exhibit  slight  indications  of  a  radially  fibrous 
structure.  They  are  usually  located  along  fine  lines  of  minute  dots  on  the 
surface  of  the  obsidian.  The  small  blue  spherules  are  generally  crowded 
together  along  these  lines,  or  more  properly  along  the  planes  of  which  these 
lines  are  the  traces,  and  which  are  planes  of  flow.  Sometimes  a  number  of 
layers  will  lie  close  together  with  the  thinnest  possible  sheet  of  black  glass 
between  them,  or  they  will  unite  to  form  a  baud  a  fourth  of  an  inch  thick, 
whose  surface  is  covered  with  protruding  hemispheres.  Occasionally  groups 
of  spherules  are  prolonged  in  one  direction,  forming  parallel  ropes  through 
the  black  glass. 

The  surface  of  the  spherules  is  brown  or  red,  and  constitutes  a  plane 
of  weakness  between  the  siiherulite  and  the  glass,  along  Avhich  the  two 
separate  with  ease,  leaving  a  dull  pitted  surface  on  the  obsidian.  The 
arrangement  of  the  spherulites  in  the  plane  of  flow  is  quite  iiTegular,  though 
occasionally  in  arborescent  figures. 

Spherulites  about  the  size  of  peas  have  an  agate-like  banding  in  con- 


SPHERULITES  IN  OBSIDIAN.  •  363 

centric  shells,  combined  with  a  radially  tibrons  structure.  Their  form  is 
more  or  less  spherical,  sometimes  l)ein<^  depressed  on  one  side,  or  they  are 
eloufjated  into  <i'ourd  shapes.  They  are  frequently  agg'rej'ated  in  botryoidal 
and  kidney-shaped  groups.  Their  surface,  where  separated  from  the  obsid- 
ian, has  a  delicate  velvety  bloom,  like  that  of  a  peach,  which  in  rich  shades 
of  brown  and  teiTa  cotta  contrasts  strongly  with  the  black  glassy  matrix. 

The  larger  spherulites  an  inch  or  more  in  diameter,  are  usually  lighter 
colored,  in  shades  of  reddish  gray,  often  having  a  blue  center.  They  have 
a  more  earthy  texture  than  the  small  ones,  and  a  distinct,  radially  fibrous 
structure,  with  satiny  luster.  In  some  cases  there  is  a  granular  spotted 
appearance  in  the  outer  portion,  and  frequently  a  distinctly  concentric  struc- 
ture is  present,  the  shells  being  either  broad  and  dense  or  of  the  most  deli- 
cate thinness.  The  surface  of  these  spherulites  is  often  ridged  with  rings 
numing  parallel  to  the  flow  planes  of  the  rock,  closely  resembling  the  surface 
of  concretions  in  sedimentary  rocks.  Their  shapes  vary  from  spheroidal 
to  flattened  disks  and  hemispheres  and  irregular  forms  resulting  from  the 
interference  of  spherules  that  have  grown  close  together. 

The  delicate  -banding  of  the  rock  which  marks  its  flow  structure  passes 
uninterruptedly  through  all  these  spherulites,  although  it  is  not  always 
recognizable  without  the  aid  of  a  lens.  This  indicates  that  the  spherulites 
were  formed  after  the  lava  came  to  rest  and  when  the  parallel  layers  of 
flow  had  become  motionless.  There  is  no  deiinite  order  in  which  the 
different  kinds  of  spherulites  crystallized.  Sometimes  the  larger  ones  have 
developed  first;  in  other  cases,  the  smaller  ones. 

The  spherulites  are  not  all  solid;  the  larger  ones  especially  are  more  or 
less  porous,  often  cavernous.  The  large  earthy  ones,  which  appear  densest, 
have  microscopic  cavities  between  the  crystals  composing  them.  Others 
have  a  saccharoidal  texture  and  are  made  up  of  slightly  adhering  crystals. 
Many  of  them  have  porous  or  open  cavities  within  their  mass,  the  periphery 
often  forming  a  solid  crust  or  shell,  like  the  rind  of  a  cantaloupe.  In  some 
cases  these  cavities  ramify  through  the  heart  of  a  spherulite  and  are  coated 
with  brilliant  crystals.  The  porous  spherulites  often  resemble  pithy  berries, 
while  the  more  open  ones  appear  to  have  shrunk  and  cracked  apart,  like 
the  heart  of  an  oven'ipe  watermelon.  This  character  is  illustrated  in 
figs.  1  and  5  of  PI.  XLI.  The  cavity  is  cbnfined  to  the  limits  of  a  single 
sphenilite  when  this  occurs  isolated  in  the  rock;  detached  ones  with  per- 


364  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

fectly  continuous  shells  are  often  very  hollow  within.  Isolated  spherulites 
in  dense  black  obsidian,  without  the  trace  of  cracking,  are  sometimes  half 
hollow,  presenting  a  white  skeleton  of  crystalline  fibers  and  nodules,  or 
concentric  shells  which  are  dotted  with  minute  pellets  of  tridymite.  This 
form,  which  is  a  typical  lithophysa,  is  represented  by  fig.  3  of  PI.  XLI. 
The  shells  are  usually  so  delicate  that  parts  of  them  fall  out  when  the  rock 
is  broken.  •  On  the  white  frosted  substance  of  these  lithophysaj  rest  the 
honey-yello^y  crystals  of  fayalite,^  Avhicli  have  not  yet  been  attacked  by 
atmospheric  agencies.  In  most  other  cases  the  porous  nature  of  the  inclos- 
ing rock,  when  lithoidal,  has  allowed  these  agencies  to  attack  the  fayalite, 
when  it  is  usually  more  or  less  altered  to  an  opaque  metallic  substance, 
through  the  formation  of  ferric  oxide.  Cavities  are  less  frequent  in  the 
small  blue  spherulites,  but  occasionally  the  smallest  spherules  are  white 
and  porous;  and  in  j^laces  along  the  spherulitic  layers,  or  through  the  black 
glass,  there  are  granulated  bands  of  small  cavities  with  a  white,  gray,  or 
pink  coating. 

Besides  the  thin  blue  layers  with  spherulitic  structure,  the  obsidian  is 
also  banded  by  light-gray  ones  of  a  more  crystalline  or  porcelain-like 
nature.  As  these  become  more  numerous  the  rock  assumes  a  lithoidal  or 
stony  appearance  and  grades  into  purplish-gray  rock,  delicately  banded 
with  blue — a  lithoidal  rhyolite,  or  lithoidite  in  this  case,  since  there  are  no 
phenocrysts  in  it.  This  rock  is  thinly  fissile  in  jilates  parallel  to  the  band- 
ing, which  are  sometimes  not  more  than  one-sixth  of  an  inch  thick  (PI. 
XLII).  Occasionally  the  rock  breaks  into  blocks  which  bear  the  strongest 
resemblance  to  silicified  wood. 

The  lithoidite  is  completely  spherulitic,  but  the  spherulites  are  micro- 
scopic and  have  a  character  somewhat  diff'erent  from  that  of  those  just 
described,  the  megascopic  ones  being  almost  all  porous  or  hollow.  The  rock 
abounds  in  lithophysse  of  great  delicacy  and  beauty,  and  often  of  great  size, 
the  largest  being  a  foot  or  more  in  diameter.  An  idea  of  their  abundance 
is  given  by  fig.  2  of  PL  XLIII,  which  represents  a  slab  of  lithoidite,  in 
natural  size.  The  lithophysse  in  this  rock  are  mostly  hemispherical,  and 
consist  of  concentric  shells  which  arch  over  one  another  like  the  petals  of  a 
rosfe  (fig.  4  of  PI.  XLI  and  fig.  1  of  PI.  XLIII).  The  shallower  ones  pre- 
sent small  rose-like  centers  surrounded  by  thin  circular  shells  (fig.  2  of  PI. 

'  For  a  description  of  these  fayalite  crystals  see  the  paper  on  Obsidian  Cliff,  already  cited,  p.  270. 


U.  e.  QEOLOOICAL  auovEv 


MONOGRAPH  XXXII      PART  II      PL.   XL! 


LITHOPHYS/€. 


U.  8.  OEOLOOICAL  SURVeV 


MONOGRAPH    XXXM     PART    II     PL.    XLII 


FISSILE    LITHOIDAL    RHYOLITE,    OBSIDIAN    CLIFF 


U.   S.   OEOLOQICAL  SURVEY 


MONOORAPH  XAXtl      PART  II      PL.  XLIil 


Z.  ^'"^**^^^^«,si-^  ^ 


LITHOPHYS/E. 


u.  9.  OEOLOOieALtURVE' 


nNoi.HAPH   x^Ml      PART   II       PL.    XLIV 


COLUMNAR   RHYOLITE,    WEST   SIDE  OF  OBSIDIAN   CREEK. 


LITIIorHYSiE  AT  OBSIDIAN  CLIFF.  365 

XLIIl).  The  disks  are  sometimes  oval,  and  are  sometimes  composed  of 
several  sets  of  shells,  which  have  been  started  from  centers  near  together 
and  have  developed  in  sections,  givin<i-  a  scalloped  form  to  the  curves. 
Others  are  eccentric  or  send  out  long  curving  arms,  as  fig.  2  of  PI.  XLI. 

The  concentric  shells  are  generally  very  thin,  and  often  so  close 
together  that  in  one  histance  fifty  occur  within  a  radius  of  2  inches.  They 
are  very  fragile  and  crumble  under  the  touch,  being  made  up  of  small  and 
slightly  adhering  crystals  of  brilliant  quartz  and  orthoclase.  In  the  litho- 
physa  represented  on  natural  scale  by  fig.  1  of  PI.  XLIII  the  rose-like 
center  is  surrounded  by  delicate  shells.  The  outer  portions  to  the  right 
and  left  are  somewhat  massive,  though  finely  porons  and  crystalline,  and 
are  ti'aversed  by  well-marked  shrinkage  cracks,  which  gape  open  from  the 
base  of  the  rock  to  which  the  lithophysa  adhered,  and  clearly  indicate  the 
contraction  of  the  massive  portion.  In  the  cavities  between  some  layers 
of  the  laminated  lithoidite  there  are  small  tabular  crystals  of  sanidine,  with 
blue  iridescence.  They  are  Manebach  twins,  the  basal  pinacoid  being 
the  talnilar  plane.  They  contain  soda  and  potash  in  equal  molecular 
proportions.^ 

In  recapitulation,  then,  this  rhyolitic  lava  is  a  flow  about  100  feet 
thick,  except  where  it  has  piled  up  in  a  small  valley.  It  is  glassy,  except 
the  lithoidal  portion  in  the  valley,  and  is  free  from  phenocrysts  The 
obsidian  is  dense  in  the  lower  part  of  the  sheet  and  carries  numerous 
spherulites.  Large  vesicles  occur  in  the  upper  portion,  and  toward  the 
surface  of  the  flow  the  spherulites  disappear  and  the  glass  becomes  filled 
with  gas  cavities  and  passes  up  into  pumice.  The  lithoidal  portion  is  filled 
Avith  lithophysse  and  has  numerous  porous  layers.  These  characteristics 
repeat  themselves  in  the  rhyolite  in  various  parts  of  the  Park. 

The  columnar  structure  which  is  so  well  developed  in  this  obsidian  is 
also  observed  in  the  rhyolite  in  uiany  other  places  in  this  region.  It  occurs 
in  the  poi^phyritic  lithoidal  rhyolite  on  the  west  side  of  Obsidian  Creek, 
directly  opposite  the  clifl",  and  is  shown  in  the  accompanying  illustration 
(PI.  XLIV).  These  columns  are  short  and  stout,  about  15  feet  high  and  2 
or  3  feet  broad.  They  are  traversed  by  pronounced  jointing,  which  splits 
the  rock  into  plates  parallel  to  the  planes  of  flow.  From  the  inclination  of 
these  it  would  appear  that  the  original  surface  of  the  lava  sloped  northward 

'  Obsidian  Cliff,  loc.  cit.,  p.  267. 


366     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

somewhat  more  steeply  than  does  the  present  ridge.  Similar  columnar 
structure  occurs  in  tlie  purple  lithoidal  rhyolite  (1815)  on  Winter  Creek,  2 
miles  west  of  this  locality. 

CANYONS  OF  GIBBON   RIVER  AND  MADISON  RIVER. 

The  lava  forming  the  high  bluff  back  of  the  Paint  Pots  and  just  east  of 
the  Gibbon  River  as  it  leaves  the  Geyser  Meadow  is  a  variety  of  rhyolite 
somewliat  difterent  from  that  forming  the  plateau  country  roundabout.  It 
is  lithoidal  and  porphyritic,  like  the  occurrences  alreadj'  described,  but  is 
dull  steel-gray  in  color,  and  full  of  minute,  irregularly  shaj^ed  cavities, 
producing  a  very  rough  fracture.  The  phenocrysts  are  mostly  small  white 
feldspars,  which  are  plagioclase,  and  much  fewer  transparent  sanidines,  and 
very  rarely  quartz;  small  augites  may  be  seen  with  a  lens.  The  rock 
appears  more  like  a  Ijasalt  than  a  rhyolite.  It  passes  southward  along  the 
east  side  of  the  river  into  light-purple  lithoidal  rhyolite  with  similar  plagio- 
clases,  but  much  more  quartz  and  sanidine. 

The  Gibbon  River  after  leaving  Geyser  Meadow  cuts  a  narrow  canyon, 
500  to  600  feet  deej),  through  rhyolite,  which  is  almost  entirely  lithoidal, 
but  of  variable  character.  On  the  west  side  it  is  exposed  in  high  vertical 
cliffs  of  dark  lithoidal  rock  with  pronounced  banding  or  flow  structure, 
which  is  greatly  contorted.  Back  of  the  hot  springs  on  the  east  side  there 
are  a  number  of  angular  fragments  of  reddish-brown  glassy  rhyolite  full 
of  small  phenocrysts  of  quartz  and  feldspar  (1852).  These  are  probably 
not  in  place.  The  west  wall  near  the  bridge  consists  of  reddish-purple 
lithoidal  rhyolite,  full  of  irregular  pores,  and  crumbling.  It  is  rich  in 
phenocrysts  of  quartz  and  feldspar  (1851,  1853),  and  is  a  nevadite,  strictly 
speaking.  The  great  massive  clilf  weathers  into  columnar  pinnacles,  which 
are  very  chai'acteristic  of  crumbling  rhyolite.  The  denser  variety  of  the 
rock  weathers  into  fragments  with  smooth  surfaces  and  sharp  edges. 

At  the  falls  of  the  Gibbon  the  rhyolite  is  reddish  and  lithoidal,  passing 
into  glassy  rock,  that  at  the  base  of  the  falls  being  black  obsidian  full  of 
porphyritical  crystals,  which  is  so  thoroughly  cracked  that  it  is  difficult  to 
obtain  a  compact  liand  specimen  of  it  (1855,  1856). 

The  canyon  made  by  the  Madison  River  below  the  junction  of  the 
Gibbon  and  Firehole  rivers  has  been  cut  1,700  feet  through  the  rhyolite 
mass  without  reaching  the  underlying  rocks.     The  canyon  presents  fine 


RHYOLITK  OF  MADISON  CANYON.  367 

exposures  of  rhyolite.  A  rude  coluiunar  structure  is  plainly  seen  in  the 
rhvolite,  which  is  evidently  one  thick  sheet  and  not  a  succession  of  thin 
sheets  superimposed  on  one  another. 

The  face  of  the  cliff  on  the  north  side  of  tlie  canyon  exhibits  long, 
slender,  vertical  columns  of  rhyolite,  200  feet  high,  with  shorter  ones  some- 
what inclined.  The  U})per  part  of  the  cliff  is  traversed  by  a])proximately 
horizontal  joints,  which  arch  over  the  tops  of  the  vertical  colunnis,  a  structure 
similar  to  that  in  the  upi)er  part  of  the  glassy  end  of  Obsidian  Cliff.  The 
rhyt)lite  at  this  point  is  lithoidal,  with  numerous  small  plienocrysts,  and  is 
banded  dark  and  light  purjile.  The  lighter-colored  parts  are  finely  porous 
(1857).  West  of  this  prominent  point  the  rhyolite  is  massive,  in  nearly 
horizontal  layers,  and  weathers  into  rounded  pinnacles,  which  are  shown 
in  PI.  XLV.  The  rock  from  this  mass  breaks  into  great  rounded  blocks, 
like  granite,  and  weathers  into  angular  sand.  It  is  literally  crowded  with 
phenocrysts  of  quartz  and  sanidine,  with  abundant  small  rusted  augites, 
and  is  a  uevadite.  In  places  it  has  a  dark-purple  banded  g-roundmass  and 
is  somewhat  vesicular  (1858).  Parts  of  it  are  filled  with  hollow  spherulites, 
which  are  highly  crj^stalline  and  porous,  wdth  gaping  cracked  hollows  at 
their  centers,  which  are  encrusted  with  tridymite  and  minute  feldspars,  with 
larger  crystals  of  quartz  exhibiting  the  characteristic  steep  rhombohedral 
faces,  §  R.  There  are  also  a  few  rusted  fayalites.  In  some  instances  there 
are  indications  of  concentric  shells  (1859,  1860).  The  same  nevadite  forms 
the  summit  of  the  highest  point  of  the  north  wall  of  the  canyon  (1862). 
From  a  distance  it  appears  as  though  there  were  a  thinner  sheet  of  rhyolite 
overlying  a  very  thick  one,  the  top  of  the  lower  flow  weathering  away  and 
leaving  the  bottom  of  the  upper  one  dense  and  well  defined,  but  this 
appearance  may  be  deceptive,  since  the  rock  occurring  in  the  talus  at  the 
base  of  the  slope  is  all  one  variety,  very  rich  in  phenocrysts.  The  apparent 
difference  may  arise  from  slight  variation  in  the  physical  character  of  the 
rock  at  that  place. 

MADISON    PLATEAU,  NORTH    OF    THE    LOWER    GEYSER    BASIN. 

The  northwestern  arm  of  the  rhyolite  plateau,  west  of  Obsidian 
Creek  and  Gibbon  River  and  north  of  the  Madison  River,  covers  all  the 
lower  portion  of  the  northwestern  corner  of  the  Yellowstone  Park,  reaching 
up  the  slopes  of  the  Grallatin  Mountains  to  altitudes  of  8,000  and  8,600  feet. 


368  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

It  forms  the  long  flat-topped  spurs  extending  out  from  tlie  base  of  these 
mountains,  and  passes  under  the  Pleistocene  valley  of  the  Madison  River. 
It  carries  on  its  surface  a  few  remnants  of  a  once  extensive  basalt  sheet, 
and  in  places  has  been  er(ided  down  to  the  underlying  rocks,  which  are 
mostly  gneiss.  Throughout  most  of  this  area  the  rhyolite  is  lithoidal, 
reddish  purple,  and  slightly  porphyritic,  Phenocrysts  are  not  very 
abundant  in  the  rock  southwest  of  Mount  Holmes  (1816)  and  in  that  found 
in  the  vicinity  of  Gneiss  Creek  and  its  northeast  bi-anch  (1818  to  1820). 
At  its  extreme  northwestern  end,  north  of  Fan  Creek,  the  rhyolite  overlies 
a  conglomerate  of  andesitic  fragments,  and  is  exposed  in  a  cliff  200  feet  high, 
the  lower  portion  being  dense  and  lithoidal,  the  upper  jDart  containing  litho- 
physpe.  Small  lithophysfe  are  also  found  filling  the  dark-purple  rhyolite  on 
the  summit  of  the  ridge  to  the  west. 

At  the  l^ase  of  the  west  slope  of  the  plateau  south  of  Cougar  Creek 
the  lava  is  glassy  black  obsidian,  closely  resembling  that  of  Obsidian  Cliff, 
except  that  it  carries  a  few  small  plienocrysts.  It  is  spherulitic,  with  small 
blue  spherulites  (1864)  and  small  lithophysa?  containing  quart2;,  tridymite, 
and  fayalite.  Part  of  the  obsidian  is  filled  with  small  lithophysse,  which 
are  mostly  hollow,  gaping  spherulites,  with  very  distinct  delicate  prisnis, 
which  radiate  from  what  was  once  the  Center  of  the  pasty  spherule,  and 
consequently  ajjpear  to  have  been  formed  ])rior  to  the  cracking  and  gaping 
of  the  spherule.  The  sides  of  the  hollows  are  dotted  with  brilliant  pellets 
of  tridymite.  These  very  hollow  lithophysse,  some  of  which  exhibit  a 
tendency  toward  concentric  shells,  existed  as  hollow  bodies  with  very  slight 
but  rigid  shells  before  the  surrounding  magma  solidified,  for  a  number  of 
them  have  been  crushed  in  such  a  manner  as  to  prove  that  the  thin  shells 
were  rigid  and  that  the  matrix  was  very  viscous  and  the  pressure  not  very 
great;  for  the  glass  has  not  forced  its  way  into  the  cavities,  and  in  one  case 
did  not  fill  up  the  space  made  by  the  cracked  shell. 

At  the  west  end  of  Madison  Canyon  the  river  cuts  through  lithoidal 
rhyolite,  which  forms  the  western  foothills  of  the  plateau  south  of  the 
river.  It  is  light  colored,  with  lithophysse  and  spherulites,  and  in  one  place 
is  full  of  irregular  cavities  which  are  coated  with  crystals  of  quartz  and 
hematite.  The  quartz  is  prismatic,  with  the  unit  rliombohedrons  and  a 
steeper  one  less  strongly  develojjed,  but  perfect  when  present.  The  hema- 
tite is  in  thin  tablets  with  crystal  faces,  and  is  usually  twinned  (1867). 


VICINITY  OF  LOWER  GEYSER  BASIN.  369 

The  top  of  the  plateau  south  of  Madison  Canyon  is  ahnost  entirely 
glassy  rhyolite,  perlite,  and  obsidian.  At  the  western  edge  of  the  top,  near 
tlie  road,  is  black  i)orphyritic  obsidian,  which  is  vesicular  in  layers,  the 
vesicles  in  places  having  been  elongated  in  one  direction  and  flattened  in  a 
plane  perpendicular  to  the  layers.  With  it  is  associated  a  grayish-white 
pumice  of  the  same  magma,  into  which  it  undoubtedly  passes  (1865, 1866). 
The  edge  of  the  plateau  north  of  Sentinel  Creek  is  partl)^  lithoidal  rhyolite, 
reddish  purple,  with  abundant  prominent  sanidines  and  smaller  qviartzes 
(1877,  1878),  some  of  it  containing  beautiful  white  lithophysfe  with  con- 
centric shells  (1873).  But  the  greater  part  of  the  rock  is  obsidian  or  per- 
lite, with  the  same  i)henocrysts  as  the  lithoidal  portion  of  the  rock.  Much  of 
it  is  spherulitic,  having  abundant  small  blue  or  red  spherulites,  both  com- 
pact and  porous,  with  radial  fibration  and  concentric  zones.  Through  these 
spherulites  the  phenocrysts  are  scattered  indiscriminately,  not  appearing  to 
act  as  a  nucleus.  Larger  spherulites  occur,  and  more  typical  lithophysse 
(1874  to  1876),  and  the  obsidian  in  places  is  red  and  black,  especially 
in  the  small  alcoves  and  arroyos  along  the  southern  edge  of  the  plateau. 
The  eastern  side  of  this  block  of  table-land  is  a  cliff  from  300  to  500  feet 
hiffh,  at  the  base  of  which  runs  the  Firehole  River.  The  rock  is  lithoidal 
and  banded,  while  along  the  east  bank  of  the  river  above  the  falls  the 
rhyolite  is  glassy  for  the  most  part. 

VICINITY    OF    LOWER    GEYSER    BASIN. 

On  the  east  bank  of  Firehole  River  east  of  Madison  Plateau  the  rhyo- 
lite occurs  with  marked  layer  structure.  The  layers,  which  are  bent  and 
folded,  trend  almost  parallel  to  the  direction  of  the  stream.  The  rock 
exhibits  great  variability.  Some  of  it  is  lithoidal,  dense,  purple,  and 
banded.  Much  of  it  is  black  perlite,  with  small  blue  spherulites  in  layers, 
so  crowded  together  as  to  leave  but  small  patches  of  perlite  glass;  other 
layers  are  microspherulitic  (1869).  Large  spherulites  are  scattered  through 
the  rock,  together  with  numerous  phenocrysts  of  sanidine  and  quartz,  which 
exhibit  no  connection  with  the  layer  structure  so  far  as  their  distribution  is 
concerned,  but  show  a  tendency  for  the  longer  crystals  of  feldspar  to  lie 
more  nearly  parallel  to  the  layers  than  transverse  to  them. 

The  perlite  outcrops  in  long  ridges  j^arallel  to  the  river,  and  stands  in 
nearly  vertical  layers  of  alternating  characters,  including  spherulitic  perlite, 

MON  XXXII,  PT  II 24 


370     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

purer  glass,  and  red  pumice,  witli  layers  of  litliopliysse.  This  is  shown  in 
PI.  XLVI,  Avhich  represents  several  masses  of  this  rock  that  have  been  eroded 
into  rude  monuments  situated  about  a  mile  above  the  lower  falls.  The  ver- 
tical layers  are  well  shown  in  the  illustration.  The  small  monument  is  filled 
with  lithophysse.  A  few  hundred  yards  above  the  falls,  on  the  east  bank, 
there  is  an  exposure  of  black  perlite  bearing  very  large  lithophysn?,  from 
1  to  2  feet  in  diameter  (1870).  This  is  shown  in  PI.  XL VII.  Some  are 
compact  spherulites,  with  little  if  any  cavity,  purplish  red  in  color,  and 
breaking  with  radiating  cracks.  Others  have  distinct  coiicentric  shells,  one- 
fourth  of  an  inch  thick,  with  a  spherical  nucleus,  which  is  shrunken  and 
cracked,  and  have  large  cavities.  The  radiate  crystallization  is  very  pro- 
nounced in  the  more  porous  parts  of  the  lithophysse,  and  the  feldspar  rays 
can  be  seen  with  a  pocket  lens.  They  are  studded  with  minute  brilliant 
and  transparent  crystals  of  tridymite,  and  the  sides  of  the  cavities  are  spotted' 
with  pseudomorphs  of  fayalite,  like  those  at  Obsidian  Cliif. 

The  rock  in  which  these  remarkable  bodies  occur  is  a  black  and  gray 
perlite,  full  of  small  sjoherulites  and  phenocrysts,  some  layers  of  the  rock 
being  very  dense.  They  stand  vertical  and  in  places  are  much  bent.  Most  of 
the  perlite  is  ver}'  crumbling,  and  consists  of  gray  glass}^  shells,  surround- 
ing rounded  and  subangular  grains  of  black  glass,  which  weather  out  into 
black  sand.  The  small  spherulites  are  beautifully  banded  in  concentric 
shells,  being  blue  at  the  center  and  red  outside  (1868). 

Where  the  river  near  this  place  cuts  a  narrow  gorge  through  the  rhyo- 
lite,  the  rock  is  lithoidal  and  banded.  Farther  south,  at  the  end  of  the  i-idge 
east  of  the  river,  about  2  miles  below  the  mouth  of  Nez  Percd  Creek,  there 
is  a  breccia  of  ]5erlite  and  lithoidal  rhyolite  carrying  fragments  of  an  almost 
fibrous  variety  (1871),  pieces  of  which  were  found  west  of  the  road  4  miles 
north  of  the  Lower  Geyser  Basin  (1872).  It  is  lithoidal  and  porphyritic, 
and  is  traversed  by  long,  slender  pores  so  close  together  as  to  produce  a 
fibrous  structure,  the  fibers  curving  around  the  phenocrysts.  The  sides  of 
the  elongated  vesicles  are  coated  with  white  pellets  of  tridymite,  the  rock 
itself  being  dark  slate  color. 

Brecciated  rhyolite  occurs  a  short  distance  to  the  southeast,  in  the  first 
low  ridge  north  of  the  Nez  Perc(i  Creek.  North  of  this  the  low  ridges  are 
covered  with  light-red  pumiceous  glass,  delicately  banded  with  black,  pro- 
ducing the  most  perfect  and  beautiful  lamination.     It  is  rich  in  phenocrysts 


U.   8.   GEOLOGICAL  SURVEY 


MONOGRAPH  /XXII      PART   I       PL.    XLVII 


PERLITE   WITH   SPHERULITES,    FIREHOLE   RivER, 


VICINITY  OF  LOVVEK  GEYSER  BASIN.  371 

of  aanidine  and  smaller  (jiiartzes,  the  larger  feldspars  lying  parallel  to  the 
lamination  (187!t).  This  pumice  passes  into  dark-gray  porphyritic  perlite, 
full  of  red  and  blue  splierulites  (1882).  In  })laces  it  contains  lithophysaj 
several  inches  in  diameter,  with  wide  gaping  centers,  which  have  Iseen 
crushed  and  dislocated  to  some  extent,  and  into  the  cavities  of  which  the 
viscous  matrix  was  in  some  instances  foi'ced. 

Rhyolite  exhibiting  variations  similar  to  those  just  described — lithoidal, 
glassy,  perlitic,  pumiceous,  spherulitic  or  with  lithophysai — forms  the  pla- 
teau northeast  of  the  Lower  Greyser  Basin  and  north  of  Nez  Perc^  Creek 
(1890,  1891).  On  its  southern  edge,  about  3  miles  east  of  the  Lower  Geyser 
Basin,  the  bluff  exposure  is  rhyolite,  which  is  lithoidal  and  beautifully  lam- 
inated, or,  perhaps  more  properly  speaking,  streaked  in  layers,  the  dark 
purplish-gray  rock  being  marked  with  lighter-colored  lines  or  streaks,  which 
appear  to  be  more  highly  crystallized,  and  are  spotted  with  minute  round 
holes  about  the  size  of  a  pin  point  (1884).  In  a  neighboring  exposure,  where 
the  bluff  on  the  south  side  approaches  the  river,  the  banded  rhj^olite  is  light 
reddish  purple  streaked  with  yellow  (1883).  It  is  filled  with  plienocrysts  of 
sanidine  and  smaller  quartzes,  which,  however,  are  scarcely  noticeable 
except  on  close  examination,  because  of  their  transparency  and  the  general 
mottling  of  the  rock.  The  rock  is  parted  in  parallel  plates,  which  appear 
to  be  independent  of  the  direction  of  the  flow  structure  and  stand  at  all 
angles  in  the  cliff.     In  one  place  the  jointing  is  semicircular. 

The  plateau  south  of  Ngz  Percti  Creek  and  east  of  the  Lower  Geyser 
Basin  is  of  the  same  character  as  that  north.  Lithoidal  rhyolite  alternates 
with  much  glassy  rhyolite,  which  is  in  many  places  a  very  fine  gray  perlite. 
Southwest  of  the  broad  valley  at  the  forks  of  Nez  Percd  Creek  there  is  a 
breccia  of  gray  perlite,  some  fragments  of  which  are  of  large  size.  It  is 
both  compact  and  vesicular  to  pumiceous,  the  vesicles  being  flattened  and 
elongated  (1885  to  1887).  The  southeast  branch  of  this  stream  cuts  a 
narrow  gulch  through  black,  porphyritic  obsidian,  which  is  so  thoroughly 
cracked  that  it  weathers  into  a  black  sand.  Glassy  breccia  occurs  in 
other  places  over  this  plateau  (1889).  A  very  remarkable  form  of  com- 
pactly spherulitic  rhyolite  is  also  found  sparingly.  It  is  megascopically 
axiolitic,  the  spherulitic  crystallization  ha^^ng  taken  place  from  short,  curved 
planes  that  cross  one  another  at  all  angles,  and  also  from  most  of  the 
phenocrysts  which  act  as  nuclei  of  small  splierulites.     The  result  is  a  brown 


372     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

and  blue  mottled  rock  which  on  a  smooth  jointing  siirface  exhibits  a  curious 
pattern  of  curved  blue  lines  and  spots  (1892).  The  numerous  gulches  and 
small  canyons  around  the  east  and  southeast  corner  of  the  Lower  Geyser 
Basin  afford  excellent  opportunities  for  studying  the  character  of  the  rhyo- 
litic  lava  in  this  neighborhood.  Fine  exposures  of  perlite  and  obsidian, 
more  or  less  spherulitic  and  usually  associated  with  lithoidal  rhyolite,  are 
found  in  many  places. 

On  the  north  side  of  the  mouth  of  the  canyon  south  of  that  draining 
into  Hot  Lakes  spherulitic  rhyolite  is  exposed  in  which  spherulites  from 
the  size  of  large  shot  to  an  inch  in  diameter  constitute  almost  the  entire 
rock  mass.  In  places  where  they  are  very  closely  packed  together  the 
exposures  when  seen  from  a  short  distance  have  the  appearance  of  even- 
grained  conglomerate  or  bits  of  pebbles  or  coarse  gravel.  Exposures  of 
such  character  occur  man}"  feet  in  vertical  thickness  and  many  yards  in 
horizontal  extent.  Farther  up  this  canyon  vesicular  rhyolite  and  fine  gray 
perlite  are  exposed  (191(j,  1920). 

Similar  gray  perlite  with  very  perfect  perlitic  structure  forms  the  bluff 
on  the  east  side  of  the  Firehole  River  opposite  Excelsior  Geyser.  It  is  full 
of  small  phenocrysts  and  is  slightly  vesicular  (1904,  1905).  In  places  it  is 
lithoidal.  It  is  separated  into  nearly  horizontal  layei"s  by  joints  which  curve 
down  to  the  northward  at  a  somewhat  stee^jer  pitch  than  the  slope  of  the 
hill,  indicating  the  descent  of  the  lava  into  a  basin-like  depression  to  the 
north  and  the  subsequent  erosion  of  the  top  of  the  hill.  There  is  a  tendency 
to  prismatic  jointing.  The  slope  of  the  bluff  farther  south  is  covered  with 
a  fine  sand  of  perlitic  grains.  Porphyritic  rhyolite  of  the  same  variable 
character  forms  the  spurs  around  the  drainage  of  Rabbit  Creek 

The  spur  of  the  plateau  southwest  of  the  Lower  Geyser  Basin  has  a 
precipitous  wall  on  the  north  and  east  sides,  which  exposes  lithoidal  por- 
phyritic rhyolite,  the  top  of  the  plateau  being  almost  wholly  glassy  perlite 
and  cracked  obsidian,  which  form  the  canyon  of  the  Little  Firehole  River 
near  its  falls  (1922,  1923). 

UPPER  GEYSER  BASIN. 

Though  the  plateaus  on  all  sides  of  the  Upper  Geyser  Basin  are 
normal  rhyolites  like  the  various  forms  just  described,  the  rock  in  the  imme- 
diate vicinity  of  the  great  geysers  of  this  basin  is  abnormal.     It  is  a  dull 


VICINITY  OF  UPPER  GEYSER  BASIN.  373 

lithoidal  rock,  slate  color  speckled  witli  li<>lit  gray,  carrying  abundant  phe- 
nocrvsts  of  feldspar,  most  of  which  a'v  white  or  yellow  and  exhiliit  brilliant 
striated  cleavage  planes.  There  are  none  of  (juartz.  This  rock  resembles 
that  forming  the  bluti"  at  the  southeast  corner  of  Geyser  Meadow.  It  is 
exposed  in  the  rounded  hills  back  of  the  Splendid  Geyser  (1924),  and  in 
tabular  masses  back  of  the  Grand  (1926),  and  forms  the  west  bank  of  the 
Firehole  Kiver  east  of  Old  Faithful  Geyser.  The  microscopical  features  will 
be  described  in  another  place.  Its  extent  and  its  relation  to  the  normal 
rhvolite  of  the  neighborhood  were  not  made  out.  Perlite  with  large 
spherulites  occurs  on  the  bank  of  the  Firehole  River  a  short  distance  above 
Old  Faithful  Geyser  (2166,  2167). 

Above  the  Upper  Geyser  Basin  the  road  along  the  Firehole  River 
traverses  rhyolite  like  that  of  the  plateau,  for  the  most  part  lithoidal,  and 
weathering  into  crumbling  sand.  Through  it  the  river  has  cut  a  narrow 
rocky  channel  which  is  tilled  with  great  masses  of  rhyolite  that  have  fallen 
from  the  steep  sides.  Just  below  Keplei's  Cascade  the  river  passes  through 
a  narrow  gate  in  a  channel  not  more  than  2  feet  wide.  The  cut  exposes 
vertical  layers  of  spherulitic  rhyolite,  mostly  lithoidal  (1933),  the  layers 
ci'ossing  the  stream  at  right  angles. 

Following  the  southeast  branch  of  the  Firehole  River  to  the  pass  of  the 
old  trail  near  the  north  end  of  Shoshone  Lake,  one  traverses  country  covered 
with  lithoidal  and  glassy  rhyolite.  For  long  distances  the  road  lies  in  a  line 
glassy  sand  derived  from  the  disintegration  of  perlite.  The  clitf  that  stretches 
for  3  miles  along  the  south  side  of  the  road  presents  a  variety  of  phases  of 
rhyolite.  At  its  western  end  it  is  lithoidal  and  very  porous  and  vesicular, 
with  here  and  there  patches  and  streaks  of  glassy  rock.  Farther  east  the 
glassy  rock  predominates,  with  smaller  masses  of  lithoidal  rhyolite.  Near 
the  pass  south  of  the  road  well-banded  lithoidal  rock  abounds,  and  at  the  • 
pass  glassy  and  spherulitic  modifications  occur,  as  varied  as  those  of  Obsidian 
Cliff.  The  vesicular  lithoidal  rock  at  the  west  end  of  the  cliff  is  lig-ht 
bluish  gray,  discolored  by  brown  and  yellow  stains.  It  carries  numerous 
phenocrysts,  which  are  so  transparent  as  to  be  easily  overlooked.  The  small 
irregular  vesicles  are  not  distributed  uniformly  through  the  rock,  as  is  usually 
the  case  in  basalt,  but  are  very  unequally  scattered,  being  abundant  in 
some  spots  and  almost  absent  from  others.  This  is  a  very  common  mode 
of  occurrence  in  the  lithoidal  rhyolite  of  this  region  (1934,  1935).     The 


374     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

well-banded  lithoidal  portiou  near  the  pass  is  dark  slate  colored,  striped  witli 
layers  of  light  purplish  gray,  often  of  the  utmost  delicac)',  in  this  respect 
resembling  the  laminated  lithoidal  part  of  Obsidian  Cliff.  There  are  occa- 
sionally small  cavities  with  transparent  tabular  crystals  of  sanidine  and 
some  of  quartz.  The  phenocrysts  are  abundant,  and  consist  of  sanidine, 
plagioclase,  and  quartz,  with  numerous  rusted  crystals  of  a  ferromagnesian 
mineral,  which  has  been  found  to  be  augite.  The  longer  phenocrysts  lie 
more  or  less  parallel  to  the  lamination  (1937).  Some  of  the  obsidian 
contains  small  black  spherulites,  the  size  of  small  shot.  Other  parts  of  it 
are  streaked  with  red  and  brown  glass  (1936).  The  most  perfect  perhtic 
structure  is  developed  in  places,  together  with  curiously  crenulated  cavities 
that  traverse  the  rock  in  streaks  and  are  coated  with  crystalline  grains, 
which  in  some  instances  appear  to  be  fragments  of  broken  phenocrysts  of 
feldspar  (1939-1940)  that  have  been  dragged  apart  along  the  line  of  the 
cavity. 

MADISON   PLATEAU   SOUTH   OF  THE  GEYSER  BASINS. 

The  whole  of  this  plateau  is  rhyolite,  mostly  black  glassy  obsidian, 
with  porphyritical  crystals,  in  places  spherulitic.  This  alternates  with 
pumiceous  glass,  which  occurs  in  bands  or  layers.  The  alternation  of  dense 
and  pumiceous  glass  is  very  persistent  over  the  whole  top  of  the  plateavi,  but 
the  majority  of  outcrops  consist  of  the  denser  obsidian,  since  the  pumiceous 
portions  of  the  rock  have  been  more  easily  eroded.  The  character  of  the 
country  and  of  the  rocks  is  very  monotonous  and  uniform,  varied  only  in 
the  neighborhood  of  Summit  Lake  by  small  areas  of  hot  springs  and  fuma- 
roles.  The  top  of  the  plateau  soutliwest  of  tlie  Upper  Geyser  Basin  is 
glassy,  but  the  lower  part  of  the  bluff  along  Iron  Spring  Creek  is  lithoidal 
gray  rhyolite,  more  or  less  porous  and  vesicular.  The  shallow  drainage 
channels,  as  the}^  approach  the  edge  of  the  plateau,  drop  into  deep  ravines, 
where  are  large  streams  of  water  which  are  not  met  with  on  the  top  of  the 
plateau.  The  water  comes  from  the  edge  of  the  plateau,  out  of  the  mass  of 
the  rhyolite,  the  upper  portion  of  which  is  porous  and  vesicular,  while  the 
lower  part  is  dense  and  compact.  The  smaller  of  the  streams  draining  south- 
westerly into  Boundary  Creek,  east  of  Buffalo  Lake,  cuts  a  gulch  150  feet 
in  the  edge  of  the  bluff  which  forms  the  east  wall  of  the  basin  of  Buffalo 
Lake.  The  gulch  has  vertical,  rocky  walls,  exposing  a  fine  section  of  the 
rhyolite  lava,  the  flow  of  which  has  been  greatly  contorted.     The  lowest 


MADISON  PLATEAU.  375 

portions  of  the  cliflf  are  l)luisli-}.Tay  litlioidiil  rli^-olitc,  passin<--  up  into  black 
and  red  obsidian  (19')!)  with  small  plienocrysts.  Tlie  rock  is  richly  spher- 
ulitic,  witli  large  lithophysa'  in  thick  layers.  Tlie  lava  sheet  is  slaggy  on 
top,  with  layers  that  have  been  stretched  and  cracked  transversely.  From 
the  structure  of  the  lava  it  is  evident  that  the  flow  poured  down  a  steep 
slope  westward  into  the  valley  basin  of  Buffalo  Creek.  The  jiresent 
eastern  wall  is  a  bluff  150  to  200  feet  high.  Farther  down  Boundary 
Creek,  as  far  as  the  bluff  north  of  Falls  River  Basin,  the  rhyolite  is  lithoi- 
dal,  but  the  bluff  west  of  the  falls  of  lioundary  Creek,  forming  the  edge  of 
the  plateau,  is  black  and  red  spherulitic  and  porphyritic  obsidian  (1950). 
The  same  observation  was  made  by  Professor  Penfield  in  traveling  from 
Madison  Lake  across  the  southern  end  of  the  plateau  to  Falls  River  Basin. 
The  whole  surface  of  the  country  is  black  obsidian  and  grayish-white 
pumice  (1941,  1942),  which  is  porphyritic  with  large  sanidines  and  smaller 
quartzes,  but  as  the  level  of  the  basin  is  approached  the  rock  grows 
lithoidal. 

On  the  continental  divide  south  of  Madison  Lake  the  black  obsidian 
is  in  some  places  finely  vesicular  and  in  others  spherulitic,  with  small  litho- 
physfe  coated  with  tridymite  pellets  and  containing  a  small  amount  of 
fayalite.  It  incloses  many  angular  fragments  of  very  fine-grained  basalt, 
which  is  often  highly  vesicular  and  which  has  the  petrographical  characters 
of  the  so-called  "recent  basalts."  Similar  inclosed  fragments  of  basalt  were 
found  in  various  places  northwest  of  this  locality.  They  indicate  the 
existence  of  basalt  flows  in  this  vicinity  prior  to  the  outbreak  of  the  top 
sheet  of  rhyolite,  but  no  large  body  of  basalt  was  observed. 

BECHLER    CANYON. 

Bechler  River  cuts  a  fine  canyon  through  the  great  rhyolite  mass,  thus 
separating  Madison  Plateau  from  Pitchstone  Plateau.  The  canyon  trends 
in  a  northeast-southwest  direction  and  exhibits  a  very  marked  diffei-ence 
between  its  western  and  eastern  walls.  The  former  is  a  rather  i^ersistent 
bluff  800  feet  high,  while  the  latter  is  from  1,000  to  2,000  feet  in  height, 
presenting  the  greatest  thickness  of  rhyolite  exposed  within  the  Park. 

The  rock  of  the  country  forming  the  northern  head  of  Bechler  River 
has  the  character  of  that  on  the  surface  of  the  plateaus,  the  rhyolite  being 
mostly  glassy  and  pumiceous,  in  some  places  crowded  with  spherulites,  in 


376  GEOLOGY  OF  THE   YELLOWSTONE  NATIONAL  PARK. 

Others  perlitic.  Parts  of  it  are  lithoidal.  Before  the  valley  commences  to 
canyon,  at  an  altitude  of  about  7,900  feet,  the  stream  cuts  its  way  through 
lithoidal  rhyolite,  well  laminated  and  much  contorted,  with  most  of  the 
layers  standing  in  a  vertical  position.  Below  this  the  stream  continues  to 
cut  through  dark-gray  porphyritic  rhyolite,  which  is  lithoidal  and  finely 
banded,  while  on  the  top  of  the  western  wall  at  the  upper  end  of  the 
canyon  pi-oper  the  rock  is  glassy  and  beautifully  spherulitic  in  irregularly 
shaped  forms,  inclosing  grains  of  obsidian,  and  producing  the  appearance 
of  large  axiolites  on  the  surface  of  the  rock  in  a  manner  already  described. 
It  also  contains  small  hollow  spherulites,  distinctly  fibrous  (1946),  and 
passes  into  highly  vesicular  to  pumiceous  lithoidal  rock,  light  bluish  gray 
in  color  (1945). 

Half  a  mile  above  the  mouth  of  Bechler  Canyon  the  rock  exposed  in 
the  stream  bed  is  dense  lithoidal  rhyolite  (1949).  It  forms  the  bed  of  the 
stream  up  to  near  Colonnade  Falls,  which  is  about  a  mile  above  the  mouth 
of  the  canyon.  Here  the  rhyolite  is  overlain  by  a  horizontal  sheet  of  basalt 
which  is  at  the  same  altitude  as  that  of  the  great  basalt  sheet  in  Falls  River 
Basin,  a  tongue  of  which  must  have  flowed  up  into  the  canyon.  It  gives  rise 
to  Colonnade  Falls,  where  the  stream  drops  60  feet  from  a  ledge  of  rock  into 
a  basin  partly  inclosed  by  a  semicircular  wall  of  colunmar  basalt.  At  the 
base  of  this  wall  the  large  vertical  columns  are  30  feet  high;  they  pass  up 
into  irregularly  cracked  basalt,  which  at  the  top  is  massive  and  vesicular, 
forming  a  layer  which  projects  over  the  face  of  the  wall.  The  wet  columnar 
rock  forms  a  dark  background  for  the  free-falling  water  with  its  rainbowed 
mist,  while  the  banlcs,  kept  moist  by  the  shifting  spray,  are  covered  with  a 
luxuriant  growth  of  ferns  on  the  one  side  and  of  flowers  on  the  other. 

A  hundred  yards  upstream  is  Iris  Falls,  about  40  feet  higli,  of 
diff'erent  character.  It  is  broad  and  is  broken  by  large  masses  of  rock  at 
its  base.  The  rock  is  porphyritic  rhyolite,  which  is  a  later  flow  than  the 
basalt,  and  must  have  been  a  small  one  in  the  bottom  of  the  canyon.  The 
lower  portion  of  this  later  flow  of  rhyolite  is  glassy,  being  a  spherulitic 
obsidian  (1961),  and  is  brecciated  with  inclosed  masses  of  older  rhyolite. 
It  grades  upward  hito  lithoidal  rock  which  is  light  gray  colored  (1948). 
This  passes  up,  at  the  top  of  the  falls,  into  black,  glassy,  and  spherulitic 
forms  again.  Half  a  mile  farther  upstream  is  another  waterfall,  of  60  feet, 
having  the  same  general  character  as  the  last.     It  cuts  through  the  later 


FALLS  ItlVER  BASIN.  377 

sheet  of  rhyolite,  which  is  finely  exposed  on  the  east  wull.  In  tlie  bottom 
portion  of  the  flow  nix'  h>r<>t'  masses  of  inclosed  rock.  The  central  layer  is 
massive,  with  well-marked  planes  of  flow.  A  short  distance  upstream  are 
fine  double  cataracts,  and  above  these  are  others  in  continuous  succession, 
the  river  descending  in  all  about  150  feet.  The  rocks  on  both  sides  of  the 
can\'on  appear  to  be  soaked  with  water,  which  runs  into  the  river  from  a 
multitude  of  small  streams  and  springs  along  the  base  of  the  walls. 

FALLS   RIVER   BASIN. 

Falls  River  Basin,  which  in  reality  is  a  terrace  of  the  great  plateau,  at 
an  altitude  of  from  6,300  to  6,500  feet,  is  about  15  miles  long  and  8  miles 
wide.  It  is  a  portion  of  the  vast  rliyolitic  lava  flow,  which  is  partially 
covered  by  a  thin  sheet  of  basalt.  The  river  has  cut  its  way  down  to  the 
rhyolite,  which  forms  the  bed  of  the  stream  from  a  point  1  mile  below  the 
mouth  of  Boundary  Creek  down  as  far  as  explored,  below  Boone  Creek. 
The  rhyolite  is  lithoidal  and  fissile,  and  at  the  falls  below  the  mouth  of 
Falls  River  there  is  evidence  of  more  than  one  flow  of  rhyolite.  The  upper 
of  these  falls  is  a  cataract.  The  middle  one  is  a  beautiful  fall,  15  or  20  feet 
high  and  about  200  feet  wide,  with  a  cascade  in  low  steps  above  it.  At  the 
west  end  of  this  fall  there  is  a  low  arched  cave,  formed  by  a  sheet  of  dense, 
gray,  glassy  rhyolite,  with  small  pheuocrysts  (1952),  overlying  a  mass  of 
brecciated  glassy  rhyolite,  which  is  more  easily  eroded.  Above  the  gray 
layer  the  rhyolite  is  glassy  and  spherulitic  (1956),  passing  up  into  banded 
lithoidal  rock.  The  exposure  appears  to  be  that  of  the  bottom  of  a  lava 
flow.  The  third  waterfall  is  broad  and  low,  not  more  than  5  feet  hia-h. 
About  2  miles  above  the  mouth  of  Boone  Creek  there  is  another  fall,  where 
the  river  cuts  50  feet  into  the  rhyolite,  leaving  isolated  blocks  of  .the  rock 
standing  like  monuments  in  the  stream.  The  rhyolite  forms  a  bench  on 
both  sides  of  the  river,  with  bluff's  of  basalt  100  feet  high  standing  back  a 
short  distance.  This  branch  canyon  of  the  Snake  River  begins  to  assume 
the  same  geological  character  which  the  deeper  canyon  of  the  main  stream 
possesses  in  the  neighborhood  of  Shoshone  Falls,  Idaho,  where  numerous 
sheets  of  columnar  basalt  overlie  a  glassy  and  lithoidal  dacite  of  peculiar 
characters,  which  closely  relate  it  to  the  rhyolite  of  the  Yellowstone  National 
Park. 

The  valley  of  Conant  Creek,  just  north  of  the  forty-fourth  parallel  of 


378  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

latitude,  is  cut  into  litlioidal  rhyolite,  which  is  somewhat  spherulitic  and  is 
filled  with  small  phenocrysts  (1955).  This  rhyolite  continues  south  beyond 
the  limits  of  the  area  explored  and  forms  the  northwestern  base  of  the 
foothills  of  the  Teton  Range  up  to  an  elevation  of  over  8,000  feet.  Where 
it  has  Ijeen  cut  across  by  the  valley  of  Conant  Creek  its  contact  with  the 
underlying  rocks  is  seen  to  be  very  steeply  pitched  to  the  west,  indicating 
how  steep  the  preexisting  surface  must  have  been  at  this  place.  The  rhyo- 
lite near  the  contact  is  rudely  columnar.  It  is  part  of  the  great  lava  flood 
which  buried  the  slopes  of  the  northern  foothills  of  the  same  range,  and  is 
found  overlying  sedimentary  and  Archean  rocks  and  volcanic  breccias  of 
andesite  which  had  accumulated  on  them.  About  the  head  of  Conant  and 
Boone  creeks  and  along  Berry  Creek  thin  tongues  of  the  rhyolite  sheet, 
continuous  with  the  heavy  mass  of  Pitchstone  Plateau,  have  been  left  in 
favored  places,  and  have  escaped  the  erosion  which  must  have  considerably 
modified  the  contour  of  the  surface  in  the  vicinity  of  this  high  range  of 
mountains.  These  portions  of  the  lava  lie  at  higher  altitudes  than  the  top 
of  the  plateau  north,  and  even  exceed  in  some  places  the  highest  elevation 
of  the  main  body  of  Pitchstone  Plateau.  In  two  points  north  of  Berry 
Creek  the  altitude  of  the  pi'esent  surface  of  the  rhyolite  is  8,900  feet,  and 
just  east  of  Forellen  Peak  it  reaches  9,300  feet,  resting  in  a  thin  sheet  on 
sedimentary  rocks. 

The  petrographical  character  of  tlie  rhyolite  varies  somewhat  in  this 
neighborhood,  but  the  variations  are  mainly  due  to  the  fact  that  the 
exposures  are  in  many  cases  at  or  near  the  bottom  of  the  lava  flow,  where 
it  has  been  aff'ected  by  coming  in  contact  with  underlying  rocks.  Thus,  on 
the  west  slope  of  the  mountain  north  of  the  head  of  Conant  Creek  the 
mass  of  the  rhyolite  is  lithoidal  and  but  slightly  porphyritic,  but  near 
the  bottom  of  the  flow  it  is  in  places  black  obsidian  (1958)  with  a  fine 
mottling  that  is  almost  imperceptible  and  is  more  pronounced  in  a  gray, 
glassy  form  of  the  rock  (1954)  fi'om  the  same  locality,  which  is  similar 
to  that  at  the  middle  falls  on  Falls  River  (1952).  In  places  the  lithoidite 
is  light  bluish  or  purplish  gray  and  has  large  flattened  vesicular  cavities 
intimately  related  to  hollow  spherulites  and  lithophysoe  (1953,  1957).  These 
exhibit  characteristic  V-shaped  cracks,  and  have  evidently  resulted  from  the 
gaping  open  in  spots  of  a  viscous  substance.  They  are  coated  with  yellow- 
stained  crystals  of  the  same  minerals  as  those  which  occur  in  lithophysae, 


FALLS  RIVER  BASIN.  37i) 

and  around  tlie  cavity  the  rock  is  lif^liter  colored.  Another  modification 
of  the  rock,  which  lias  numerous  small  i)henocrysts  of  quartz,  occurs  2  miles 
northeast  of  Survey  Peak.  It  is  laminated  and  fissile  in  thin  ])lates,  resem- 
bling a  schist  (1960).  A  similar  form  of  rhy elite  is  found  on  the  long  spur 
east  of  Snake  River,  opposite  the  mouth  of  Owl  Creek.  The  rhyolite  cap- 
ping the  limestone  on  the  divide  between  Berry  and  Conant  creeks  belongs 
to  the  nevadite  tyi)e,  being  filled  with  phenocrysts.  Near  its  contact  with 
the  limestone  it  is  dark  slate  colored,  glassy,  and  spherulitic  (1959).  It 
grades  upward  into  lighter-colored,  purplish,  and  yellow  lithoidal  nevadite, 
full  of  irregularly  shaped  ca^^ties.  It  weathers  in  great  rounded  and 
roughened  masses  like  granite.  The  same  is  tiaie  of  the  rhyolite  in  the 
neighborhood  of  Birch  Hills,  in  the  valley  to  the  northeast,  and  at  Terrace 
Falls.  Here  the  coarsely  jjorphyritic,  reddish-purple  rhyolite,  or  nevadite, 
has  been  weathered  and  eroded  into  great  rounded  towers  100  feet  high, 
which  resemble  exposures  of  coarsely  crystalline  granite. 

It  is  to  be  remarked  that  while  the  rhyolite  in  the  vicinity  of  Birch 
Hills  is  lithoidal  along  the  valleys  cut  by  both  forks  of  Falls  River  at 
altitudes  of  from  6,700  to  7,000  feet,  j^et  within  the  amphitheater  at  the 
head  of  Mountain  Ash  Creek  the  stream  at  7,000  feet  cuts  a  narrow  canyon 
through  porous  and  glassy  rhyolite,  which  also  forms  the  spur  on  the  north 
side  of  the  amphitheater  at  7,350  feet,  where  it  is  black  porphyritic  obsidian 
and  perlite.  This  is  1,200  to  1,500  feet  below  the  edge  of  the  Pitchstone 
Plateau,  where  the  rhyolite  is  black  and  red  spherulitic  obsidian  with  many 
phenocrysts  (1972).  Farther  down  Mountain  Ash  Creek,  at  an  altitude  of 
6,800  feet,  where  two  branches  unite  at  the  crest  of  Union  Falls,  80  feet 
high,  the  rhyolite  is  lithoidal.  The  occurrence  of  glass)"  forms  of  rhyolite 
in  the  bottom  of  this  amphitheater  overlying  lithoidal  ones  indicates  that 
this  was  the  surface  of  a  flow,  aiid  not  the  interior  jjortion  of  one  which 
has  been  exposed  by  the  erosion  of  a  vast  amphitheater. 

PITCHSTONE  PLATEAU. 

One  of  the  most  interesting  exposures  of  rhyolite  is  that  furnished  by 
the  high  spur  between  the  branches  of  Glade  Creek,  a  tributar}-  of  the 
Snake  River,  which  enters  the  latter  about  5  miles  north  of  the  forty-fourth 
parallel  of  latitude.  The  spur  is  from  600  to  1,000  feet  high,  and  at  its 
southern  end   presents  a  high  bluff  of  lithoidal  rock,  exhibiting  greatly 


380  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

contorted  bands  of  flow.  Its  base  consists  of  a  talus  of  large  blocks.  The 
rhyolite  is  dark  gray,  speckled  with  white  and  brown.  It  bfears  many 
phenocrysts  of  white  plagioclase  and  fewer  of  quartz  and  sanidine,  besides 
many  small  rusted  crystals  of  augite  (1964,  1966,  1967).  Through  the 
rock  are  scattered  cavities  of  various  sizes  and  shapes  with  gray  or  white 
walls,  which  are  coated  with  brilliant  crystals  of  quartz,  tridymite,  or  sani- 
dine, with  opaque  crystals  of  faj-alite.  The  quartzes  have  been  studied  b}^ 
Professor  Peniield,  who  has  found  them  to  have  a  simple  but  very  unusual 
development.  In  addition  to  the  common  quartz  forms — prism  and  unit 
rhombohedrons — there  are  steep  rhombohedrons  (3032),  3/2  and  (0332), 
3/2,  and  narrow  trapezohedral  faces  rb  3/2-3/2.^ 

The  same  rare  forms  occur  on  the  quartzes  in  the  lithophysse  at 
Obsidian  Cliff"  and  in  other  localities  within  the  Yellowstone  Park.  The 
white  walls  of  these  cavities  vary  in  thickness  from  mere  lines  to  an  inch, 
and  some  of  them  have  a  distinctly  spherulitic  structure  with  widely  gaping 
centers.  They  are  in  part  hollow  spherulites  of  a  peculiar  character,  very 
closely  related  to  the  irregular  cavities  in  the  rock,  which  could  not  be 
termed  spherulites.  The  outei-  margin  of  the  hollow  spherulites  is  not 
shai-ply  defined  against  the  groundmass  of  the  rock,  as  in  most  instances. 
The  radial  fibration  is  not  recognizable  V)y  the  unaided  eye,  and  a  concen- 
tric zonal  structure  is  observed  in  only  a  portion  of  them.  The  most 
characteristic  feature  of  these  hollow  spherulites  is  the  occurrence  of  com- 
paratively large  quartz  crystals  in  two  habits,  usually  in  diff"erent  parts  of 
the  cavity.  One  form  of  the  quartz  consists  of  stout  crystals,  seldom  over 
2  mm.  in  diameter,  in  one  iiistance  6  mm.,  very  transparent,  with  a  pale 
smoky  to  amethystine  color.  The  others  are  slender  white  prisms,  10  nmi. 
long.  The  transparent  crystals  are  often  located  on  a  nearly  flat  side  of 
the  cavity,  while  the  white  prisms,  intersecting  in  all  directions,  form  a  kind 
of  network  which  occupies  the  thicker  part  of  the  center  of  the  spherulite. 
The  light-colored  streaks  and  more  crystalline  parts  of  the  rock  are  punc- 
tured with  minute  round  holes.  Along  the  cliff"  to  the  westward  the  rock 
passes  into  laminated  lithoidal  rhyolite  with  open  layers  incrusted  with  the 
same  minerals  as  those  in  the  cavities  just  described. 

The  rhyolite  on  the  second  ridge  east  of  Glade  Creek  is  black  and 


I  Iddings  aud  Pentield,  Tho  minerals  in  hollow  spherulites  of  rhyolite  from  Glade  Creek,  Wyo- 
ming: Am.  Jour.  Soi.,  3d  series,  Vol.  XLII,  1891,  p.  39. 


MOUNT  SHBKIUAN.  381 

brown  Dbsidijui,  witli  iiiiiiiy  plu'iiocrysts  and  small  splnTulites.  The  splieru- 
lites  have  crystallized  around  plienocrysts  as  nuclei  in  many  cases.  There 
are  also  small  crenulated  cavities,  which  lie  indiscriminately  in  the  glass 
and  spherulites  and  are  coated  with  minute  crystals  (1968,  1969).  These 
curious  cavities  occur  in  the  rock  ot"  Obsidian  Clitf  and  elsewhere  in 
the  Park. 

RED   MOUNTAINS. 

On  the  edg-e  of  the  plateau  of"  rhyolite  which  lies  between  the  Yellow- 
stone Lake  and  Snake  River  rises  a  small  group  of  mountains,  whose  highest 
peak  at  the  eastern  end  is  ]\Iount  Sheridan  (10,200  feet).  It  is  an  east-west 
ridge  with  four  prominent  spurs  trending  north  and  south,  sejjarated  by 
deep  amphitheaters.  Its  summits  are  from  1,500  to  !2,000  feet  above  the 
plateau,  but  the  eastern  peak  is  2,700  feet  above  Heart  Lake,  which  lies  at 
its  base.  The  slopes  and  spurs  on  the  east  and  north  are  short  and  steep, 
and  only  the  southern  ones  fall  away  gradually  to  tlie  level  of  the  jilateau. 
These  mountains  are  of  rhyolite,  whose  character  in  the  body  of  jMount 
Sheridan  ditfers  somewhat  from  that  of  the  plateau.  On  the  steep  north- 
eastern spur  south  of  the  Heart  Lake  Geyser  Basin  much  of  the  rhyolite 
is  white  and  gi'ay  lithoidal  rock,  with  a  moderate  number  of  small 
phenocrysts,  in  some  places  very  few,  and  belonging  to  the  variety  liparite. 
The  main  mass  of  Mount  Sheridan  and  the  ridge  immediately  west  is 
composed  of  this  dense  liparite,  which  is  light  purplish  gray  in  color  and 
fissile  in  thin  plates  (1980).  Similar  rhyolite  occurs  near  the  top  of 
the  ridge  and  on  the  summit  of  Mount  Sheridan,  where  it  is  coated  with 
hyalite  in  places  and  contains  many  transparent  crystals  of  tridymite  in 
thin  fissures  (1984).  The  rhyolite  on  the  top  of  the  ridge  and  on  the  upper 
northern  slope  and  summit  of  Mount  Sheridan  is  brecciated,  but  it  is  com- 
pact, and  is  evidenth*  brecciated  flow  rock  and  not  an  aggregation  of  loose 
fragments  and  dust,  which  is  the  case  with  almost  all  of  the  andesitic  breccia 
of  this  region.  In  places  on  the  summit  the  rhyolite  is  brown  and  glassy, 
and  the  brecciated  portion  is  intersected  by  dikes  of  massive  banded  lithoidal 
rhyolite  of  no  considerable  extent.  This  appears  to  be  the  only  instance 
in  which  anything  resembling  a  dike  of  rhyolite  has  been  observed  in  the 
Yellowstone  Park.  All  of  the  rhyolite  exposures  observed  b}^  the  writer 
appeared  to  be  surface  flows  of  lava  resting  upon  older  rocks.  In  the  cases 
where  later  bodies  of  rhyolite  have  been  recognized  they  have  always  been 


382     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

ill  the  form  of  surficial  flows,  the  orifices  or  fissure  through  which  they 
reached  the  surface  not  being  exposed  to  view.  This  is  most  noticeably 
the  case  in  the  outlying  remnants  of  thin  sheets  whose  jjlane  of  contact 
with  the  underlying  rocks  is  frequently  observed. 

The  eastern  face  of  Mount  Sheridan  is  composed  of  massive  white 
and  gra}'  liparite,  like  the  northeastern  spur.  The  upper  portion  of  the 
long  northern  spur  consists  of  a  heavy  flow  of  rhyolite,  about  700  feet 
thick,  which  appears  to  have  the  same  character  as  the  plateau  rock. 

In  the  neighborhood  of  Lewis  and  Sho.shone  lakes  the  rhyolite  exhibits 
variations  from  lithoidal  to  glassy  forms.  The  bluff  west  of  Lewis  River 
at  the  crossing  of  the  old  trail,  2J  miles  below  Lewis  Lake,  exposes 
very  fine  lithoidal  rhyolite,  mottled  dark  and  light  gray,  which  is  porphy- 
ritic  and  banded  (1971).  The  top  of  the  plateau  west  and  north  of  Lewis 
Lake  is  mostly  glassy  or  hyaline  rhyolite — black  and  red  obsidian  and 
perlite,  which  is  spheruhtic  and  porpliyritic  (1973).  This  may  be  observed 
along  the  trail  between  the  two  lakes.  The  character  of  the  rhyolite  on 
the  east  side  of  Shoshone  Lake  near  its  outlet  is  particularly  varied.  It  is 
porpliyritic  and  is  streaked  with  black  and  red  glass  and  blue  spherulitic 
layers,  besides  blue  lithoidal  portions,  weathering  pink  on  the  exposed 
surface.  The  lake  l)each  is  made  up  of  very  irregularl}'  shaped  pebbles 
of  this  rhyolite,  wliich  are  but  partially  rounded  and  form  a  beautiful 
variegated  sand. 

VICINITY  OF  YELLOWSTONE  LAKE. 

The  most  striking  A-ariability  in  the  rhyolitic  lava,  however,  is  found 
along  the  shores  of  the  Yellowstone  Lake.  The  many  miles  of  coast  offer 
numerous  bluffs  which  have  been  cut  into  the  surface  of  the  great  rhyolite 
sheet,  and  the  slightly  glaciated  hills  of  the  plateau  country  immediately 
west  of  the  lake  shore  present  all  possible  modifications  of  this  variable 
lava. 

A  good  example  of  this  is  found  in  the  cliff  on  the  second  point  south 
of  the  mouth  of  the  West  Arm  of  the  lake  and  the  first  one  north  of  Flat 
Mountain  Arm.  Here  red  and  black  glassy  forms  occur,  separately  and 
also  intimately  mixed.  The  rock  is  porphyritic  and  more  or  less  spheru- 
litic. There  are  masses  of  black  obsidian  completely  shattered  by  irregular 
tracks,  which  cause  it  to  crumble  readily  into  small  angular  fragments,  and 


WEST  OF  YELLOWSTONE  LAKE.  383 

otliers  t)t'  dark  and  liglit  bruwuisli-red  obsidian  canying-  dark-blue  splieru- 
lites  with  gray,  brown,  or  i)urple  outer  shells,  also  completel}'  crackled. 
lilack  and  red  streaked  obsidians  alternate  in  layers  with  bands  of  densely 
spherulitic  material,  and  occasionally  of  porous  spherulites.  In  places  the 
lamination  is  ,very  pronounced,  and  thin  spherulitic  layers,  when  l)rokeu 
from  the  obsidian,  are  covered  Avith  wart-like  excrescences,  which  are 
protruding-  spherulites,  ribbed  with  parallel  lines  corresponding  to  the  planes 
of  lamination  of  the  rock.  Parts  of  the  rock  are  fissile  and  consist  of  lioht- 
brown  glass  streaked  with  black  and  red  in  small  blotches,  and  even  rather 
large  lumps,  wliich  have  been  di-awn  out  into  lenticular  shapes  during  the 
flow  of  the  rock  (1994  to  1998). 

Pumiceous  glassy  rhyolite  forms  the  top  of  the  plateau  in  many  places 
about  the  West  Arm  of  the  lake.  Southwest  of  Riddle  Lake  the  drainao-e 
exposes  light-gray  pumice  overlying  black,  glassy,  porphyritic  rhyolite  or 
obsidian.  Lower  downstream,  near  the  forks,  the  rhyolite  is  lithoidal, 
purplish  gray,  and  banded,  and  is  accompanied  by  black  glassy  varieties 
carrying  spherulites,  which  are  the  commoner  kinds  over  this  part  of  the 
jjlateau. 

In  the  immediate  vicinit}'  of  Duck  Lake  light  and  dark  gray  pumice 
and  perlite  form  a  brecciated  flow  (1986  to  1989),  while  farther  west  the 
rhyolite  is  in  places  lithoidal.  At  Rock  Point  porphyritic  obsidian  with 
small  spherulites  occurs  in  a  brecciated  mass.  The  surface  of  the  spheru- 
lites and  of  the  glass  immediately  in  contact  with  them,  as  well  as  that  of 
the  obsidian  blocks,  is  dark  red,  like  other  portions  of  the  body  of  obsidian 
in  many  places.  There  is  also  black  perlite  with  small  lithophysfe;  and 
light-brown  and  black,  streaked  and  blotched  perlite,  and  silvery-grav 
fibrous  pumice  (2003,  2004). 

An  idea  of  the  great  diversity  of  the  rhyolite  along  the  west  shore  of 
the  lake  may  be  gotten  from  several  typical  exposures  in  the  neighborhood 
of  Bridge  Bay,  from  which  extensive  collections  have  been  made.  On  the 
south  side  of  Bridge  Creek,  about  a  mile  west  of  the  lake,  a  branch  stream 
has  cut  into  brecciated  pumiceous  and  hyaline  rhyolite.  It  is  porphyritic 
and  partly  spherulitic  crackled  obsidian  and  perlite,  with  many  small 
roughened  cavities.  The  brecciated  portion  contains  some  fragments  which 
are  2  feet  in  diameter.  A  highly  vesicular  modification  of  it  is  almost 
fibrous,  owing  to  the  elongation  of  the  vesicles,  which  have  been  drawn  out 


384     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

in  thin  tubes.  This  form  of  the  rock  is  microspheruhtic  or  lithoidal,  with 
some  glassy  portions,  and  the  breccia,  which  is  largely  composed  of  this 
material,  is  the  same  as  that  which  occurs  on  the  Firehole  River  a  short 
distance  below  the  Lower  Geyser  Basin  (2020  to  2023).  A  more  varied 
occurrence  is  crossed  l)v  the  trail  in  a  coulee  about  a  mile  south  of  Bridge 
Creek.  It  is  mostly  glassy  and  is  full  of  phenocrysts  of  quartz  and  feldspar. 
One  black  ])rojecting  mass  of  rock  consists  of  finely  vesicular  to  pumiceous 
perlitic  obsidian.  This  grades  into  a  light  reddish-brown  pumiceous  breccia 
inclosing  fragments  of  white  pumice  with  light-brown  borders  and  small 
fragments  of  light-brown  pumice  and  pieces  of  black  obsidian.  This  passes 
into  a  dense  red  ^Jerlite  mottled  with  black  and  gray,  and  the  latter  grades 
into  reddish-br(iwn  and  also  dark  drab-colored  perlite,  which  in  turn 
passes  into  spherulitie  obsidian  banded  with  minutely  spherulitic  or  lithoi- 
dal layers  full  of  small  roughened  cavities.  It  is  scoriaceous  in  places  and 
exhibits  a  great  variety  of  colors  on  weathered  surfaces  (2013  to  2019). 
All  this  variation  of  texture  and  color  takes  place  within  a  distance  of  100 
feet.  Farther  south  the  rhyolite  becomes  more  lithoidal  in  places,  purplish 
lithoidal  and  spherulitic  bands  being  intermingled  with  obsidian  and  jjerlite. 
It  is  often  roughly  vesicular  and  slag-like  (2014).  The  modifications  of 
rhyolite  just  described  constantly  recur  over  the  plateau  in  this  vicinity. 

A  still  more  varied  assortment  of  rhyolite  is  found  in  a  low  bluff  on  the 
lake  shore  half  a  mile  south  of  Bridge  Bay.  It  consists  of  brecciated  pumice 
and  scoria,  with  some  massive  lava,  and  appears  to  be  the  surface  or  the 
forward  end  of  a  flow  of  porphyritic  rhyolite.  The  colors  of  the  rock,  all 
of  whose  varieties  appear  to  be  textural  modifications  of  one  magma,  range 
from  jet  black  through  different  shades  of  gray  to  almost  white,  besides 
reds  which  are  dark  liver  colored  to  pink,  and  browns  that  are  reddish  and 
others  that  approach  yellow.  These  colors  occur  separately  in  large  masses 
or  are  combined  in  brecciated  bodies  in  blotches  and  streaks,  or  as  mottlings 
and  bandings  in  massive  rock.  The  greater  j^art  of  the  rock  is  glassy,  but 
some  of  it  is  lithoidal.  There  is  black  crackled  obsidian  grading  into  per- 
lite banded  by  delicate  layers  of  spherulites.  Some  of  it  is  more  spherulitic 
and  carries  hollow  spherulites,  which  are  distinctly  fibrous  on  the  inside 
and  are  coated  with  tridymite  pellets.  There  is  dense  black  obsidian  so 
filled  with  hollow  spherulites  as  to  appear  like  a  porous  or  vesicular 
rock.  Black,  red,  and  brown  obsidians  occur  together,  with  and  without 
spherulites,  some  of  which  are  blue  and  red,  while  others  are  porous  and 


RIIYOLITE  SOUTH  OF  BRIDGE  BAY.  385 

hollow.     A  pitcliN-  MiU'k  obsidian  with  l)luish  metallic  luster  is  filled  with 
minute  pores   that  give  it  a  rough   fracture  surface,  besides  some  larger 
pores  which  are  pumiceous  and  generally  occur  about  the  phenocrysts,  some 
of  the  larger  feldspars  appearing  to  have  been  fractured  and  dragged  apart. 
Another  form  of  obsidian  is  so  finely  vesicular  as  to  be  almost  a  pum- 
ice; it  is  dark  gray  colored,  with  grains  of  black  glass  scattered  through  it. 
Others  are  lighter  gray,  and  the  most  pumiceous  rock  is  silvery  white  and 
fibrous.     In  the  larger  cavities  the  glass  has  been  drawn  out  to  the  finest 
threads,  like  spun  glass.     Among  the  phenocrysts  the  few  light-green  augites 
are  plainly  recognizable.     There  is  black  glass  with  bright  yellow  pumi- 
ceous spots,  and  sanidine  crystals  which  have  split  open  down  the  middle 
lengthwise,  and  others  irregularly  cracked  and  piilled  apart,  the  cracks  not 
having  become  filled  with  the  glass,  which  must  have  been  expanding  into 
pumice  at  the  time.     This  grades  into  rock  in  which  the  yellow  pumice 
preponderates  over  the  black  glass.-     There  is  perlite  of  black,  red,  and 
brown  glass  intimately  mingled  and  banded,  with  feldspars  arranged  nearly 
parallel  to  the  planes  of  flow;  also  a  light-red  dense  perlite  with  small 
black    spots.      There    is    a   light-red,    lithoidal,   fibrous,   vesicular    variety 
with  irregular  patches  and    remnants    of   black    glass,   besides  light-gray 
lithoidal  rock,  with  streaks  of  dark-gray  and  black  glass  and  porous  and 
scoriaceous  portions.     Some  of  these  forms  of  the  rhyolite  are  masses  in 
the  breccia,  but  the  more  finely  brecciated  material  presents  a  still  more 
variegated   appearance.      The    most    striking  breccia   is  a   light-red,  also 
reddish-brown,  finely  porous  glass  filled  with  lumps  of  light-gray  glass  of 
all  sizes  which  is  finely  porous  and  minutely  crackled,  besides  others  of 
dark-gray  pumice  and  rounded  lumps  of  highly  inflated  vesicular  black 
glass.     Some  of  the  black  glass  is  compact  and  occasionally  spherulitic. 
Another  form  of  breccia  consists  of  fragments  of  black  and  red  obsidian  in 
a  matrix  of  smaller  fragments  of  the  same,  most  of  which  are  red,  appar- 
ently cemented  together  by  a  porcelain-like  material,  which  is    pink  or 
white.     There  is  distinct  evidence  of  plasticity  and  flow  in  the  form  and 
arrangement  of  the  small  pieces  of  glass,  and  the  porcelain-like  portion  is 
a  crystalline  modification  of  the  magma,  which  can  be  traced  into  spheru- 
litic patches.     The  reddening  of  the  glass  seems  to  have  occuired  subse- 
quent to  its  breaking  up,  for  the  fragments  of  black  obsidian  have  a  red 
margin  or  surface  of  variable  thickness. 

MON  XXXII.  PT  II 25 


386  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

NATURAL    BRIDGE. 

Bridg-e  Creek  has  received  its  name  from  a  small  natural  bridg-e  of 
rhyolite  wliich  sjians  a  narrow  g-ulch  through  which  runs  a  tributary  to  the 
main  creek.  Tliis  bridge,  which  is  shown  in  the  illustration  (PI.  XLVIII), 
consists  of  two  vertical  slabs  of  lithoidal  rhyolite,  parts  of  the  contorted 
layers  of  lava  flow,  which  stand  about  vertical  in  this  place.  The  vertical 
layers  just  east  of  the  north  end  of  the  bridge  are  shown  in  PI.  XLIX. 
They  are  slightly  curved  and  are  separated  by  open  crevices  with  rough- 
ened scoriaceous  walls.  Of'  the  two  slabs  forming  the  bridge  the  eastern, 
or  that  seen  in  the  illustration,  is  2  feet  thick  at  its  ends  and  thinner  in  the 
middle.  There  is  a  space  of  2  feet  between  it  and  the  western  slab,  which 
is  4  feet  thick.  The  span  of  the  arch  is  about  30  feet  and  its  rise  about  10 
feet,  the  top  of  the  bridge  being  some  40  feet  above  the  creek.  The  eastern 
slab  is  traversed  by  two  vertical  cracks,  and  by  horizontal  ones  just  below 
the  base  of  the  arch.  The  rhyolite  is  porphyritic  and  lithoidal,  dark  blue- 
gray,  mottled  with  light  gray,  and  distinctly  banded  in  places.  It  bears 
numerous  holloAv  spherulites  of  considerable  size  and  many  small  lith- 
ophysse  with  delicate  concentric  shells,  but  no  small  megascopic  dense 
spherulites.  The  lithoidal  rock  alternates  with  glassy  layers  of  black 
perlite  having  dense  spherulitic  bands  and  some  large  dense  spherulites 
(2048  to  2052). 

The  large  hollow  spherulites  have  been  crushed  while  the  matrix  was 
plastic,  though  not  liquid,  for  the  broken  shells  have  been  dislocated  and 
the  sides  of  the  spherulite  forced  in  and  the  cavity  partly  tilled  by  the 
matrix.  But  this  was  not  liquid  enough  to  enter  very  far  into  the  hollow 
cavity,  nor  has  it  filled  up  the  cracks  on  the  outside  of  the  shells.  It  is 
evident  that  there  was  miition  in  the  lava  after  the  large  hollow  spherulites 
had  formed,  and  that  they  were  rigid  crystalline  bodies.  It  is  quite  as 
evident  that  the  delicate  lithopliyste  of  various  sizes  Avere  not  formed  before 
the  lava  came  to  rest,  because  they  have  not  been  crushed  in  any  case, 
although  their  shells  are  often  much  thinner  than  those  of  the  hollow 
spherulites.  Moreover,  their  eccentric  and  irregular  shapes  are  more  or 
less  in  accord  with  the  crooked  and  distorted  banding  which  marks  the 
planes  of  flow  in  the  rock.  They  Ivdve  the  same  character  as  tliose  at 
Obsidian  Clitf  and  are  highly  crystalline;  but  the  fayalites  have  been 
changed   to    light-yellow  opaque  pseudomorphs,  and  the  iron   has   been 


NATURAL   BRIDGE,    EAST  SIDE  OF   YELLOWSTONE   LAKE. 


U.   8.   GEOLOGICAL  SURVEY 


MONOORAPH  XXXII      PARI    II      ri.    XLIX 


VERTICAL    PLATES   OF    RHYOLITE,    NATURAL   BRIDGE 


RHYOLITE  OF  ELEPHANT  BACK.  387 

concentrated  to  stout  tablets  of  hematite,  with  brilHaut  crystal  faces,  some 
of  them  set  upon  the  fayalite  ))seu(lomorplis,  and  of  later  ()rii)in.  In  some 
of  the  lithoi)hysa»  hematite  occurs  without  pseudomorphs  of  fayalite.  The 
Natural  Bridge  is  one  of  the  best  localities  for  the  study  of  these  hollow 
fonns  of  crystallization. 

NORTH  AND  EAST  OF  YELLOWSTONE  LAKE. 

The  spur  of  the  plateau  lying  west  of  the  outlet  of  Yellowstone  Lake, 
and  known  as  the  Elephant  Back,  is  ribbed  and  grooved  b}'  numerous 
drainage  channels  that  cut  deep  gulches  down  its  slopes  and  permit  the 
nature  of  the  mass  of  lava  forming  it  to  be  observed.  The  surface  of  the 
slopes  and  the  top  of  the  plateau  consist  for  the  most  part  of  glassy  forms 
of  rhj^olite,  strongly  porphyritic.  Black  obsidian,  passing  into  red  pumiceous 
breccia  like  that  south  of  Bridge  Creek,  is  the  prevailing  rock,  with  occa- 
sional areas  of  lithoidal  rhyolite.  The  obsidian  is  markedly  banded  with 
parallelly  oriented  feldspars  and  layers  of  spherulites,  some  of  them  red, 
porous,  and  distinctly  fibrous,  with  white  pellets  of  tridymite,  the  feldspar 
fibers  radiating  trom  the  center  of  the  spherulite,  though  often  separated 
from  it  by  an  open  space  (2066,  2068).  But  as  the  drainage  channels  are 
followed  from  the  top  of  the  plateau  downward  the  glassy  forms  become 
less  abundant,  and  in  the  deeper  gulches  the  whole  mass  of  the  rock  is 
lithoidal  and  well  banded  (2067).  This  relationship  between  the  lithoidal 
and  the  glassy  forms  of  rhyolite  is  the  usual  one  for  the  large  flows;  the 
upper  surface  is  glassy  and  more  or  less  pumiceous,  the  lower  part  of  the 
mass  is  lithoidal,  and  the  bottom  of  the  flow,  when  exposed,  is  glassy  for  a 
variable  thickness  in  many  cases,  but  not  in  all. 

Along  the  Yellowstone  River  3  miles  below  the  outlet  of  the  lake, 
about  opposite  the  mouth  of  Thistle  Creek,  the  rhyolite  is  lithoidal  and 
purplish  gray,  not  noticeabl)^  banded,  and  full  of  phenocrysts,  of  which  the 
quartzes  are  more  perfectly  crystallized  than  in  the  greater  number  of  cases 
noticed.  This  characteristic  becomes  more  pronounced  in  the  vesicular 
brecciated  rhyolite  which  forms  a  massive  exposin-e  about  2  miles  below 
the  head  of  Thistle  Creek.  In  this  rock  well-developed  double  pyramids 
of  quartz,  with  smooth  crystal  faces,  project  into  the  cavities  of  the  rock 
and  from  broken  surfaces.  The  saiaidine  is  iridescent  in  blue  and  some- 
times in  more  brilliant  prismatic  colors.     Farther  iip  the  creek  the  rhyolite 


388  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

is  dense  and  dark  colored.  But  on  the  summit  of  the  peak,  9,000  feet  high, 
at  the  head  of  the  creek,  it  is  light  pink  and  gi'ay,  earthy  in  texture,  and 
brecciated  like  a  tutf,  with  fragments  of  andesites,  and  with  phenocrysts 
like  the  vesicular  brecciated  rock  lower  down  the  creek.  There  is  no 
evidence,  however,  that  it  is  a  tuff,  but  it  appears  to  be  a  finely  brecciated 
massive  rock,  of  the  same  kind  as  the  rhyolite  opposite  the  mouth  of  Thistle 
Creek,  except  that  the  latter  is  denser  and  not  brecciated  (2059  to  2064). 

Along  the  east  shore  of  Yellowstone  Lake  the  rhyolite  extends  from 
the  vicinity  of  Pelican  Creek  on  the  north  as  far  south  as  Brimstone  Basin, 
a  small  area  of  hot  springs  2  miles  south  of  Columbine  Creek.  It  forms  a 
sheet  of  lava  which  constitutes  the  table-land  and  flat-topped  spurs  between 
the  lake  and  the  Absaroka  Mountains,  reaching  an  elevation  of  about  8,500 
feet.  Tongues  of  it  extend  up  the  long  valleys  and  are  found  at  still  higher 
altitudes.  In  the  valley  of  Sylvan  Lake  it  forms  a  massive  bluflp  on  the 
north  side,  which  reaches  8,700  to  8,800  feet  elevation.  This  is  several 
hundred  feet  higher  than  the  divide  in  Sylvan  Pass;  still  it  has  not  been 
found  east  of  the  watershed  in  the  valleys  draining  into  the  Stinkingwater 
River.  In  the  next  valley  north  of  that  of  Clear  Creek  the  rhyolite  sheet 
is  found  at  9,000  feet.  The  rock  throughout  the  greater  part  of  this  area  is 
massive,  lithoidal,  purplish,  and  porphja-itic.  The  glassy  and  pumiceous 
parts  which  probably  formed  its  sui-face  have  been  eroded  away. 

VICINITY  OF  YELLOWSTONE  RIVER. 

The  surface  of  Central  Plateau,  which  extends  from  the  Elephant  Back 
west  to  the  head  of  Nez  Percti  Creek,  and  around  the  west  end  of  Hayden 
Valley  northward,  is  covered,  like  the  countiy  south,  with  glassy  rhyolite. 
It  is  mostly  porphyritic  black  obsidian,  more  or  less  spherulitic,  and  is  in 
places  vesicular.  On  the  south  branch  of  Alum  Creek,  a  short  distance  from 
the  road,  the  obsidian  is  spherulitic  and  carries  lithophyspe  and  hollow 
spherulites  from  1  to  6  inches  in  diameter  (2072,  2073).  The  obsidian  in 
jjlaces  is  traversed  by  jointing  planes,  along  which  the  surface  of  the  rock 
is  smooth  and  polished,  but  slightly  uneven  and  warped.  The  crystals  of 
quartz  and  feldspar  have  been  cut  across  smoothly  in  most  instances,  though 
in  many  cases  the  plane  of  jointing  has  curved  around  the  end  of  a  crystal, 
or  followed  the  cleavage  of  the  feldspar  when  this  was  nearly  coincident 
with  the  plane  of  jointing.     A  small  elevation  and  depression  extends  for 


CENTRAL  PLATEAU.  339 

a  short  distance  i'rom  each  of  the  larger  crystals,  all  being  parallel  and 
pointed  in  one  direction.  They  appear  as  though  they  had  resulted  from 
the  resistance  offered  by  the  jjlienocrysts  to  a  slieariug  stress.  The  hill  south 
of  the  hot  springs  east  of  j\Iarys  Lake  is  formed  of  porphja-itic  perlite, 
full  of  small  hollow  spherulites  and  lithophysa^,  which  have  been  partly 
altered  by  the  action  of  heated  vapors,  which  come  up  throuo-h  it  and 
deposit  crystals  of  sulphur.  The  phenocrysts  of  feldspar  and  the  spheru- 
lites are  much  decomposed,  the  quartzes  and  grouudmass  remaining  unal- 
tered. The  hollow  spheruHtes  are  partly  filled  with  opal,  and  less  often 
with  sulphur  (2070). 

The  top  of  the  plateau  from  the  north  side  of  Hayden  Valley  to  Gib- 
bon River  and  Grebe  Lake  is  covered  with  porphyritic  glassy  rhyolite  or 
obsidian,  in  places  spherulitie.  This  is  the  character  of  the  rock  along  the 
road  from  the  Yellowstone  Falls  to  the  valley  of  the  Gibbon,  and  along  the 
west  bank  of  Yellowstone  River  from  Alum  Creek  to  Cascade  Creek.  At 
the  north  side  of  the  mouth  of  Otter  Creek  there  is  much  silver-ora^^ 
pumice,  which  is  beautifully  fibrous,  exhibiting  a  satin-like  sheen  Avhen  the 
light  is  reflected  from  the  sides  of  the  fibers,  but  appearing  dark  gray  and 
vitreous  on  transverse  surfaces.  It  is  filled  with  phenocrysts  (2084  to  2089). 
A  somewhat  similar  pumice,  or  more  correctly,  a  highl}^  vesicular  porphy- 
ritic perlite,  occurs  in  a  small  gulch  west  of  the  Upper  Falls  of  the  Yellow- 
stone. It  forms  a  loosely  adliering  breccia  of  pumice  and  perlite.  Some 
masses  of  perlite  are  quite  dense,  with  only  small  vesicles,  but  most  of  it  is 
greatly  inflated,  Avith  flattened  cavities.  In  places  the  perlitic  structure  is 
not  complete,  lea^-ing  kernels  of  iiTegularly  sliaped  obsidian,  which  weather 
out  and  cover  the  ground  with  black  sand  (2080  to  20S3).  In  the  meadow 
of  Cascade  Creek  south  of  Dunraven  Peak  the  rhyolite  exposed  in  the 
creek  bed  is  finely  vesicular  lithoidal  rhyolite,  purplish  gray,  with  many 
phenocrysts  of  plagioclase  and  fewer  of  sauidine  and  quartz  (2092,  2093). 
The  rock  closely  resembles  that  which  forms  the  bluff  at  the  southeast 
comer  of  Geyser  Meadow  and  also  the  rock  of  the  Upper  Geyser  Basin. 

VICINITY    OF    THE    GRAND    CANYON    OF    THE    YELLOWSTONE. 

Since  the  topographic  and  scenic  features  of  the  Grand  Canyon,  and 
the  character  and  condition  of  the  rocks  forming  it,  are  described  in  detail 
by  Mr.  Arnold  Hague  in  Part  I  of  this  monograph,  it  is  not  necessary 


390     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

to  repeat  any  of  the  petrograpliical  description  of  the  rhyoHte  in  this,  its 
most  notable,  exposure.  There  is,  however,  an  occurrence  of  cokimnar 
cracking  in  an  inconspicuous  locality  which  is  of  considerable  petrological 
interest  on  account  of  its  bearing  on  the  general  question  of  the  production 
of  jirismatic  parting,  and  which  may  properly  find  a  place  in  this  chapter. 

The  fine  columnar  parting  on  the  east  side  of  the  canyon  north  of 
Agate  Creek  are  described  in  Part  I.  Here  the  columns  are  80  feet 
long  and  several  feet  in  diameter.  But  the  prismatic  cracking  to  be 
described  occurs  in  a  small  gulch  on  the  west  wall  of  the  canyon  a  mile 
south  of  Deep  Creek.  The  rhyolite  forming  the  upper  part  of  the  plateau 
at  this  place  is  lithoidal  and  porphyritic,  light  purplish  gray,  with  a  rough 
fracture.  It  is  jointed  in  broad  blocks  which  weather  into  rough  granite- 
like masses.  This  passes  downward  into  more  distinctly  columnar,  denser 
rhyolite,  which  is  exposed  on  the  south  side  of  the  gulch  in  a  beautifully 
columnar  cliff  300  feet  high.  The  vertical  columns  are  so  regular  in  shape 
that  they  may  be  easily  mistaken  at  a  little  distance  for  basaltic  ones. 

On  the  north  side  of  the  gulch  thei'e  is  a  ledge  of  columnar  basalt  100 
feet  thick  resting  upon  gravel  and  andesitic  breccia.  Immediately  overly- 
ing the  basalt  is  the  bottom  contact  of  a  younger  flow  of  rhyolite.  The 
lowest  portion  is  tuffaceous  and  yellow,  passing  i;pward  into  denser  material, 
and  this  into  dark-gray,  brownish,  porphyritic  glass,  which  has  cracked  in 
thin,  straight  prisms,  some  quadrangular,  others  irregularly  shaped.  The 
prisms  vary  in  size  from  4  to  8  inches  long  and  from  one-third  to  three- 
fourths  of  an  inch  thick,  and  thicker.  This  glass  grades  into  lithoidal 
purplish  rock,  which  is  also  cracked  into  small  prisms  and  columns.  Some 
of  these  are  3  or  4  feet  long  and  4  inches  thick;  others  are  very  small, 
about  6  inches  long,  and  irregularly  shaped,  like  prisms  of  starch.  They 
are  more  or  less  curved,  and  occur  grouped  together  in  the  form  of  large 
blocks,  whose  relation  to  the  original  form  of  the  whole  mass  was  not  made 
out.  They  appear  to  have  resulted  from  a  shrinkage  within  these  blocks. 
The  jointing  planes  which  constitute  the  faces  of  these  prisms  or  columns 
intersect  the  many  porphyritical  crystals  of  quartz  and  feldspar,  producing 
smooth  faces,  which  show  that  the  groundmass  of  the  rock  was  rigid  Avhen 
the.  cracking  took  place.  The  small  columns,  in  their  shape  and  arrange- 
ment, are  precisely  like  those  formed  in  dried  starch. 


RIIYOLITR  NEAR  THE  LAMAK  RIVER.  ,       391 

NORTHEASTERN    CORNER    OF    YELLOWSTONE    PARK. 

Toward  the  northeast  the  rliyolite  sheet  thins  out  and  overhes  the 
andesitie  and  okler  rocks,  which  had  previously  been  <rreatly  eroded.  East 
of  the  Yellowstone  Canyon  the  plateau  top  consists  of  rhyolite,  into  which 
have  been  cut  the  canyons  of  Broad,  Deep,  and  A^ate  creeks.  The  rhyolite 
reaches  an  altitude  of  9,000  feet  where  it  is  found  in  contact  with  the 
basalt  of  IVIirror  Plateau,  and  also  on  the  peak  northwest  of  the  headwaters 
of  Broad  Creek.  At  the  latter  place  the  rock  is  red,  glassy,  and  somewhat 
pumiceous  (2058),  with  abundant  phenocrysts  and  included  fragments  of 
obsidian  Down  the  drainage  channels  from  the  summit  of  this  point  the 
rhyolite  is  denser  and  vesicular  and  contains  large  lithophysse,  while  still 
lower  down  it  is  dense,  banded,  and  lithoidal.  In  the  cliff  east  of  Mirror 
Lake  the  rock  is  dense,  has  small  phenocrysts,  and  exhibits  characters 
that  are  found  in  the  parts  of  the  sheet  near  its  Ijottom  contact.  There  is 
rhyolite  along  the  west  base  of  Amethyst  Mountain  and  Specimen  Ridge, 
where  it  constitutes  the  margin  of  the  great  plateau.  Beyond  this  to  the 
north  and  east  it  occurs  only  as  disconnected  remnants,  which  lie  at  all 
altitudes  on  the  slopes  and  summits  of  mountains  and  in  the  bottoms  of 
valleys,  in  almost  every  instance  forming  a  bench  or  table  of  greater  or  less 
prominence. 

Southeast  of  MnTor  Plateau  rhyolite  forms  a  flat-topped  spur  between 
'  Mist  and  Cold  creeks,  lying  between  the  altitudes  of  8,750  and  8,300  feet. 
East  of  the  mouth  of  Cold  Creek  it  forms  a  flat  spur,  and  stretches  from 
8,000  to  8,600  feet,  reaching  to  within  200  feet  of  the  bottom  of  Lamar 
River,  while  on  the  spur  east  of  this  it  lies  between  8,200  and  8,650  feet 
elevation  In  eack  of  these  occurrences  the  rhyolite  is  lithoidal,  purple, 
and  porphyritic. 

The  flat  spurs  and  ridges  on  the  east  side  of  Lamar  River  from  the 
base  of  Saddle  Mountain  to  Cache  Creek  are  rhyolite,  which  also  occurs 
in  isolated  patches  within  200  feet  of  the  river  at  Opal  Creek  and  at  the 
south  base  of  Bison  Peak,  and  also  within  a  short  distance  of  Amethyst 
Creek.  The  character  of  the  rhyolite  in  these  places  is  quite  the  same, 
being  purple  and  lithoidal,  with  small  phenocrysts  (2135,  2155,  2161).  This 
is  also  the  character  of  remnants  of  the  rhyolite  sheet  that  occur  on  the 
north  side  of  the  northwest  end  of  Specimen  Ridge  (2158),  and  in  a  bench 
north  of  the  mouth  of  Lamar  River,  600  feet  above  the  stream  (2157),  and 


392  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

also  on  the  east  slope  of  Garnet  Hill  (2160).  All  of  these  patches  are 
vindoubtedly  portions  of  one  continuous  sheet,  Avhich  has  been  almost  com- 
pletel}^  eroded. 

Remnants  of  the  rhyolite  sheet  lie  high  up  the  slopes  of  Saddle 
Mountain,  even  near  its  summit.  One  area  is  on  the  west  spur  of  the  peak 
southwest  of  Saddle  Mountain,  at  an  altitude  of  from  9,200  to  9,500  feet. 
Near  the  bottom  contact  the  rhj'olite  is  dense  and  dark  colored;  higher  up 
in  the  mass  it  is  somewhat  fissile,  forming  thick  slabs.  It  is  lithoidal,  with 
traces  of  black  glass,  and  is  dark  colored  and  carries  small  pheuocrysts 
and  lithophyspe  (2141).     It  rests  directly  upon  basaltic  breccia. 

On  the  northwest  spur  of  the  peak  of  Saddle  Mountain,  about  700  feet 
below  the  summit,  there  is  a  small  patch  of  rhyolite  forming  a  nearly 
horizontal  sheet  not  more  than  150  feet  in  length.  It  rests  upon  basaltic 
breccia,  which  is  plainly  exposed  in  the  steep  faces  of  the  narrow  ridge. 
At  the  bottom  of  the  rhyolite  is  white  rhyolitic  tuff;  over  this  is  fissile, 
light-gray,  lithoidal  rhyolite  with  small  phenocrysts  (2137).  This  passes 
up  into  dark-colored  s^^herulitic  and  glassy  rhyolite  with  lithophysse  and 
small  phenociysts  (2138),  similar  to  the  rhyolite  on  the  spur  to  the  west. 
There  are  patches  of  rhyolite  at  various  altitudes  on  the  northwest  spur, 
down  to  8,000  feet.  At  about  this  altitude  in  the  gulch  south  of  this  spur 
and  of  Miller  Creek  there  is  a  small  group  of  fumaroles  in  rhyolite  that  is 
partly  dense  and  light  gray,  and  is  jointed  in  rectangular  plates  and  small 
straight  prisms,  and  is  partly  perlitic  and  glassy  (2145  to  2149). 

Rhyolite  covers  the  southern  portion  of  the  flat -topped  sjDur  north  of 
Miller  Creek,  and  patches  of  it  occur  on  the  ridge  near  Parker  Peak,  at 
9,500  feet,  and  on  the  south  slope  of  the  divide  at  the  head  of  Lamar  RiA^er, 
at  9,800  feet.  In  the  last  two  places  the  rock  is  partly  lithoidal,  with  small 
phenocrysts,  and  partly  glassy.  Some  of  it  is  fissile  and  some  of  it  massive, 
carrying  lithophysse.  None  of  it  has  been  found  on  the  north  side  of  the 
divide,  in  the  drainage  basin  of  Crandall  Creek.  Scattered  patches  of  it 
occur  on  lioth  sides  of  Cache  Creek,  and  a  long  narrow  tongue  extends 
along  the  west  side  for  4  miles,  being  situated  between  altitudes  of  7,000 
to  8,000  feet.  In  all  these  cases  the  structure  of  the  rhyolite  masses  is  that 
of  surface  flows,  i-esting  on  an  uneven  surface  of  older  rock,  and  nowhere 
in  this  ^dcinity  was  any  of  it  exposed  in  the  form  of  a  dike  or  other  intrusive 
body. 


PETIJOGRAPHICAL  MODIFICATIONS  OF  EOYOLITE.  393 

MICKOSCOPICAl,  CIIARACTEllS   OF  THE   UlIYOLITB. 

From  the  doscription  of  the  iiief^ascopical  characters  and  the  mode  of 
occurrence  of  the  rhyoHte  just  given,  it  is  evident  that  the  rock  varies 
greatly  in  the  manner  of  its  soHdification  and  crystallization  in  restricted 
ai-eas,  as  well  as  throughout  the  whole  region.  Its  microscopical  characters, 
therefore,  may  be  expected  to  be  equally  varied.  An  examination  of  315 
thin  sections  of  this  rock  shows  that  this  is  true  within  certain  limits.  There 
is  great  variability  among  the  sections,  but  it  is  confined  to  a  definite  range 
of  crystalline  structures  and  to  a  limited  number  of  minerals,  and  is  so  often 
repeated  in  the  rocks  fi'om  different  localities  that  a  clear  idea  of  the  micro- 
scopical characteristics  of  the  rhyolite  can  be  given  only  by  treating  them 
systematically  for  the  whole  region.  It  then  becomes  a  comparatively 
simple  undertaking. 

The  phenomena  investigated  by  a  microscopical  study  are  expressions 
of  the  mode  of  solidification  of  the  lava  and  the  extent  or  degree  and  the 
manner  of  its  crystallization.  The  mode  of  solidification  of  the  rhyolitic 
lava  in  this  region  is  that  of  a  surface  flow  of  variable  thickness.  The  lava 
has  been  in  part  inflated  and  chilled  into  pumice,  or  has  exploded  and 
formed  tuff.  Parts  of  it  have  solidified  to  dense  glass,  sometimes  rendered 
vesicular  by  large  gas  bubbles.  But  the  greater  mass  of  it  has  solidified  in 
the  central  parts  of  deep  flows  or  streams,  forming  lithoidal  rock,  whose 
crystalline  character  can  not  be  recognized  by  the  unaided  eye.  The 
pumiceous  portion  occurs  at  the  top  of  the  flows,  and  passes  downward  into 
dense  glass,  which  in  deep  flows  passes  into  lithoidal  rock.  The  latter  con- 
stitutes the  center  of  the  flow,  and  generally  passes  again  into  glass  at  the 
bottom,  which  may  or  may  not  pass  into  pumice,  or  more  usually  into  tuff, 
the  pumice  having  been  ground  to  pieces  beneath  the  weight  of  the  lava 
stream. 

The  extent  or  degree  of  crystalliza.tion  in  most  cases  manifests  itself  in 
two  ways:  One  is  in  the  amount  and  kind  of  porphyritical  minerals  pres- 
ent; the  other  is  in  the  amount  of  microscopical  crystallization  that  has 
taken  place  in  the  rock,  which  has  led  to  the  production  of  microlites  and 
aggregations  of  two  or  more  minerals  in  various  kinds  of  arrangement.  It 
is  evident  in  many  instances  that  the  first-mentioned  grouj)  of  products 
resulted  from  a  process  of  crystallization  that  antedated  the  arrival  of  the 
lava  at  the  surface  of  the  earth,  for  the  porphyritical  crystals  are  scattered 


394     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PABK. 

uniformly  and  generally  through  large  masses  of  rock,  without  reference  to 
the  boundaries  of  the  rock  body — that  is,  they  are  uniformly  scattered 
through  the  pumiceous,  compact,  glassy,  and  lithoidal  portions  of  the  lava 
flow  in  a  given  locality,  or  are  entirely  absent  from  all  of  them.  It  is  quite 
as  evident  that  the  second  group  of  crystallization  products  came  into  exist- 
ence after  the  lava  reached  the  surface,  and  to  a  great  extent  after  it  had 
ceased  to  flow.  The  reasons  for  this  will  appear  upon  studying  the  micro- 
structure  of  the  various  forms  of  rhyolite,  for  they  will  be  found  to  exhibit 
a  definite  relation  to  the  form  of  the  body  of  the  rock. 

It  does  not  follow  from  this  that  the  porphyritical  crystals  or  pheno- 
crysts  were  developed  prior  to  the  act  of  eruption  of  the  lava;  on  the  con- 
trary, it  has  been  shown  elsewhere^  that  the  j^henocrysts  of  rocks  were 
probably  crystallized  during  the  act  of  eruption,  and  that  in  some  cases 
their  growth  continued  uninterruptedly  into  the  period  of  final  crystalliza- 
tion of  the  whole  magma.  But  in  the  case  of  the  rhyolite  of  this  region 
there  is  nothing  to  indicate  what  were  the  conditions  of  crystallization  in 
different  parts  of  the  rhyolite  lava  previous  to  its  arrival  at  the  surface  of 
the  earth.  There  is  simply  the  fact  that  in  places,  or  in  particular  flows, 
phenocrysts  are  entirely  wanting,  and  that  in  others  they  are  few  or  are 
very  abundant,  and  that  they  may  be  small  in  some  cases  and  large  m 
others.  The  rhyolitic  lava  of  Obsidian  Cliff"  is  an  example  of  a  compara- 
tively small  flow  in  which  no  phenocrysts  have  been  developed.  The  main 
body  of  rhyolite,  however,  is  variable  in  this  respect;  but  the  variations 
obtain  for  larger  areas  of  lava.  Let  us  first  consider  the  microscopical 
characteristics  of  the  phenocrysts. 

PHENOCRYSTS. 

The  minerals  that  have  crystallized  porphyritically  are  quartz,  sanidine, 
plagioclase,  augite,  and  magnetite.  In  this  category  may  be  included  zir- 
con, though  its  crystals  are  always  microscopic  in  size.  Its  period  of  crys- 
tallization is  the  same  as  that  of  the  phenocrysts.  The  same  may  be  said 
of  pseudobrookite,  which  is  closely  associated  with  the  iron  ores  and  zircon, 
and  also  of  apatite  and  allanite,  which  occur  sporadically. 

'Chapter  III,  ]i.  105,  and  Chapter  VII,  p.  267. 


QUARTZ  PHENOORYSTS.  395 

QUARTZ. 

The  phenocrysts  of  qiiai-tz  vary  in  amount  and  in  size  in  diflferent  parts 
or  bodies  of  the  rhyolite.     They  may  be  wholly  absent  or  quite  abundant. 
In  some  cases  they  are  4  or  5  mm.  in  diameter;  in  others,  any  size  less  than 
this,  generally  from  2  to  4  nun.      They  are  noticeably  smaller  than  the 
sandines   in    most   instances.      Their    crystal   form    is    that    of  hexagonal 
bypyramids,  formed  by  the  equal  development  of  the  plus  and  minus  unit 
rhombohedrons,  together  with  small  prism  faces,  but  the  crystals  are  often 
rounded  to  a  greater  or  less  extent  (PI.  LIV,  tig.  4).     Tliey  are  generally 
much  cracked,  the  cracks  being  largely  spheroidal,  so  that  the  quartzes  on 
rock  surfaces  usually  appear  as  rounded  grains.     In  some  instances  their 
crystal  form  is  preserved  and  they  fall  from  the  rock  in  perfect  double  pyra- 
mids.    Owing  to  the  highly  fractured  condition  of  the  quartz,  much  of  it 
falls  out  when  thin  sections  of  the  rock  are  prepared,  and .  a  false  impres- 
sion may  thus  be  gotten  of  its  relative  abundance  unless  the  thin  section  is 
compared  with  the  rock.     In  some  varieties  of  the  I'hyolite  it  is  in  excess  of 
the  other  constituents,  and  from  this  proportion  its  relative  amount  decreases 
until  it  is  entirely  absent  in  some  varieties,  which  may  be  rich  in  feldspars. 
Its  microscopical  characteristics  are  much  the  same  in  all  varieties  of 
rhyohte  from  the  Yellowstone  Park.     Its  substance  is  colorless  and  very 
pure,  except  for  well-defined  inclusions  of  glass,  and  very  rarely  crystals 
of  other  minerals.     Individuals  of  quartz  differ  in  one  rock  section  both  as 
to  outline  and  as  to  inclusions.     Distinctly  idiomorphic  crystals  occur  by 
the  side  of  rounded  ones.     Some  quartz  sections  are  free  from  inclusions, 
while  others  in  the  same  rock  section  contain  a  few  or  many  inclusions  of 
glass  and  bays  of  groundmass  (PI.  LI,  fig.  1).    The  glass  inclusions  usually 
occupy  pyramidal  cavities,  or  they  may  be  rounded;  they    are    seldom 
irregularly  shaped.     They  generally  contain  one  gas  bubble,  whose  size 
appears  to  vary  in  proportion  to  the  volume  of  the  glass  in  any  one  section. 
In  some  instances  there  are  no  gas  bubbles  present. 

The  inclosed  glass  is  in  some  cases  colorless,  in  others  brown,  as  in  the 
illustration  just  referred  to,  usually  one  character  or  the  other  prevailing 
throughout  the  quartzes  of  a  rock  section.  But  often  colorless  and  brown 
inclusions  occur  by  the  side  of  one  another  in  the  same  quartz  crystal.  It 
frequently  happens  that  the  glass  inclosed  in  the  quartz  is  different  in  char- 
acter from  that  forming  the  groundmass  of  the  rock,  when  this  is  glassy. 


396     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  inclosed  glass  may  be  colorless  and  that  of  the  gromidmass  strongly 
colored,  yellow,  brown,  or  red;  or  vice  versa.  It  often  happens  that  the 
inclosed  glass  remains  such,  though  the  groundmass  of  the  rock  becomes 
holocrystalline.  In  a  few  instances  the  colorless  glass  inclusions  contain 
minute  idiomorphic  crystals,  which  are  probably  augite,  for  in  one  case  a 
comparatively  large  crystal  exhibits  the  optical  characters  and  green  color 
of  augite.  One  glass  inclusion  contains  twenty  of  these  crystallites.  In 
another  section  two  colorless  glass  inclusions  contain  curved  trichites.  No 
fluid  inclusions  have  been  observed. 

In  the  great  majoritj"  of  cases  each  quartz  phenocryst  is  a  single 
individual,  with  perfectly  uniform  optical  orientation,  and  no  indication  of 
internal  strain  or  displacement,  except  arovmd  the  glass  inclusions  in  a  few 
instances.  In  several  rock  sections  some  of  the  phenocrysts  of  quartz  con- 
sist of  two  or  three  quartzes  grown  together,  with  more  or  less  divergent 
orientations.     They  are  partly  idiomorphic  and  partly  rounded. 

In  most  of  the  rhyolite  sections  the  quartzes  occur  entirely  isolated 
from  phenocrysts  of  other  minerals.  With  the  excej^tion  of  sanidiue,  it 
is  almost  never  observed  in  juxtaposition  with  other  minerals,  a  common 
occurrence  among*  the  phenocrysts  in  andesites,  where  several  kinds  of  min- 
erals are  often  crystallized  in  clusters.  The  phenocrysts  of  quartz  in  this 
rhyolite  almost  never  inclose  fragnients  or  crystals  of  magnetite,  zircon, 
augite,  plagioclase,  or  sanidine,  so  that  the  relative  period  of  crystallization 
of  these  minerals  with  respect  to  quartz  Avould  be  a  matter  of  conjecture 
were  it  not  for  the  fact  that  intergrowths  of  quartz  and  sanidine  in  direct 
connection  with  the  phenocrysts  of  these  minerals  occur  in  more  than  one 
modification  of  this  rhyolite.  The  intergrowth  possesses  the  well-known 
micrographic  structure,  Avhicli  is  often  strongly  and  beautifully  developed. 

This  micrographic  intergrowth  is  of  two  kinds,  or  rather  it  is  the 
result  of  two  different  phases  of  crystallization.  In  some  cases  it  belongs 
to  the  period  of  crystallization  in  which  the  phenocrysts  of  quartz  and 
sanidine  were  produced;  in  others  it  was  formed  when  the  groundmass 
of  the  rock  crystallized.  The  latter  corresponds  to  its  more  common 
occurrence  in  certain  quartz-porphyries  and  granite-porphyries,  and  will  be 
referred  to  again  in  connection  with  the  description  of  the  groundmass  of 
the  rhyolite.  The  micrographic  intergrowth  which  belongs  to  the  first 
period  of  crystallization  in  the  rhyolite  is  specially  well  developed  in  the 


INTERGKOVVTIIS  OF  QUAliTZ  AND  SANIDINE.  35)7 

lnt;-lily  inHiiti'(l  puiuire  t'roin  uuar  the  iiioutli  ot"  Otter  Creek,  mi  the  west  side 
oF  Yellowstone  Hiver,  above  the  Upper  Falls  (2084,  2088,  2089).  In  this 
pumice  of  coloi'less  glass,  almost  free  from  inicrolitic  crystallization  and 
filled  with  gas  cavities,  there  are  comparatively  large  phenocrysts  of  quartz 
and  sanidine.  In  places  where  two  of  these  minerals  lie  near  each  other 
thev  are  connected  by  a  micrographic  patch,  the  quartz  substance  extend- 
ing irregularly  beyond  the  boundary  of  the  feldspar.  In  one  case  a 
Carlsbad  twin  of  sanidine  is  filled  with  quartz  shreds,  having  one  oi'ienta- 
tion,  and  a  simple  crystal  of  sanidine  is  intergrown  with  quartz  at  one  end 
(PI.  LIV,  fig.  1).  Isolated  micrographic  patches  occur  in  the  pumice  sec- 
tions. The  structure  is  comparatively  coarse,  and  the  form  of  the  inter- 
grown minerals  is  clearly  shown. 

The  micrographic  growth  is  not  only  attached  to  distinctly  idiomoi']^)hic 
phenocrysts,  but  to  a  great  extent  has  crystallographic  boundaries.  Its 
character  as  a  primary  crystallization  in  the  molten  rhyolitic  magma  is 
beyond  question,  for,  besides  the  crystallographic  evidence  just  given,  is 
the  fact  that  the  phenocrysts  with  which  it  is  connected  contain  glass 
inclusions  which  occasionally  occur  within  the  intergrowth  itself,  being 
easily  recognized  by  their  brown  color,  the  surrounding  glass  being  color- 
less. The  intergrowth  of  quartz  and  sanidine  proves  that  the  crystallization 
of  the  phenocrysts  of  these  minerals  was  contemporaneous.  Its  occurrence 
in  highly  inflated  glass  proves  that  its  formation  antedated  the  inflation  of 
the  pumice,  which  took  place  on  its  arrival  at  the  surface  of  the  earth. 

A  slightly  different  micrographic  crystallization  is  found  in  the  rhyo- 
litic pumice  on_  the  west  shore  of  Yellowstone  Lake,  about  a  mile  sovith  of 
Bridge  Bay  (2024,  2029).  In  one  section  a  phenocryst  of  quartz  has  a 
partial  micrographic  fringe,  which  consists  of  minute  intergrowths  of  quartz 
and  feldspar,  with  the  general  form  of  feldspar  crystals,  that  project  from 
the  quartz  phenocryst  at  various  angles,  as  though  it  were  "sprouting" 
with  feldspar.  The  quartz  of  the  fringe  has  the  same  orientation  as  that  of 
the  phenocryst.  In  the  same  rock  section  are  several  isolated  micrographic 
intergrowths  of  great  delicacy  and  beauty,  like  the  microscopic  ones  in  the 
obsidian  of  Obsidian  Cliff.  In  this  instance  also  it  is  evident  that  the 
micrographic  crystallization  antedated  the  inflation  of  the  pumice. 

In  the  holocrystalline  varieties  of  the  rhyolite  there  are  instances  in 
which  quartz  phenocrysts  extend  indefinitely  into  the  suiTounding  ground- 


398  GEOLOGY  OF  THE  YELLOWSTOJfE  NATIONAL  PAKK. 

mass,  quartz  belonging  to  the  final  crystallization  of  the  rock  having 
attachefl  itself  to  the  quartz  phenocryst  with  the  same  orientation  (PL  LIV, 
fig.  4).  The  original  form  of  the  phenocryst  can  g-eneralh'  be  detected  by 
a  faint  line  of  impurities.  This  structure  will  he  desci'ibed  in  connection 
Avith  that  of  the  groundmass. 

SANIDINE. 

The  phenocrysts  of  feldspar  are  j)artly  idiomorphic,  partly  rounded, 
and  often  fragmental.  The}'  consist  of  orthoclase  and  plagioclase,  which 
are  present  in  difterent  varieties  of  the  rhyolite  in  various  proportions.  In 
some  cases  orthoclase  is  the  only  feldspar  present;  less  frequently  plagio- 
clase is  the  predominant,  if  not  the  only,  feldspar  in  porphyritical  crystals. 
The  orthoclase  usually  possesses  the  habit  of  sanidine,  and  may  be  described 
under  that  name. 

Sanidine  usually  occurs  in  simple  crystals,  5  to  7  mm.  long,  and  also 
in  Carlsbad  and  Baveno  twins,  the  latter  being  uncommon.  When  in 
unbroken  crystals,  its  usual  form  is  a  rectangular  prism  with  truncated 
edges,  furnishing  square  cross  sections  and  rectangular  longitvidinal  ones, 
often  with  the  customary  terminal  planes.  It  is  less  frequently  in  tabular 
Carlsbad  twins.  Occasionally  it  has  irregular  outlines,  caused  by  rounded 
intrusions  of  the  groundmass,  indicating  a  partial  resorption  of  the  magma. 
In  many  cases  it  occurs  in  angular  fragments,  and  sometimes  the  crystals 
are  split  in  two  and  the  parts  are  separated  by  a  stream  of  groundmass. 
In  some  crystals  the  cleavage  planes  are  well  developed  and  close  together; 
in  most  instances  they  are  poorly  developed  and  the  crystals  are  traversed 
by  irregular  cracks.  (PI.  L,  fig.  1 ;  PI.  LI,  fig.  4.)  The  substance  of  the 
sanidine  is  generally  very  pure  and  free  from  decomposition,  but  inclu- 
sions of  glass  and  groundmass  are  common.  They  are  numerous  in  some 
forms  of  the  rock,  and  are  ])artly  confined  to  crystallographic  cavities 
and  partly  occur  in  irregularly  shaped  ones.  The  g-lass  inclusions  are 
often  colorless,  often  brown,  the  two  kinds  occurring  in  the  same  crystal. 
Frequently  they  contain  more  than  one  gas  bubble,  sometimes  as  many  as 
thirteen,  which  is  in  striking  contrast  to  the  single  bubble  in  those  in  the 
(quartz  phenocrysts.  Inclusions  with  several  bubbles  are  generally  found 
in  the  feldspars  in  pumice.  Crystallites  are  less  common  in  the  glass  inclu- 
sions than  they  are  in  those  in  the  quartzes.  Sanidine  occasionally  incloses 
crystals  of  augite  and  magnetite.    It  frequently  surrounds  crystals, of  plagio- 


PLAGIOGLASE  AND  PYltOXENE.  399 

clase  with  nearly  parallel  orientation,  and  son^etimes  extends  ontward  in 
niicroaTapliic  interiiTowtli  with  (piartz  in  tlie  manner  already  desenbed,  the 
feldspar  substanee  of  the  intergrowth  having-  the  same  orientation  as  that 
of  the  inclosed  sanidine. 

Some  crystals  of  feldspar  Avitli  rectangular  outline  or  cleavage,  which 
appear  to  be  orthoclastic,  exhiljit  a  very  faint  striation  between  crossed 
nicols,  which  is  not  sufficiently  distinct  to  be  positively  determined  as  mul- 
tiple twinning,  but  which  suggests  the  microcline  twinning  which  Miigge^ 
observed  in  the  sanidine  of  certain  trachytes  of  the  Azores.  An  in-egular 
optical  ljeha\'ior  between  crossed  nicols  is  sometimes  observed,  by  which  the 
extinction  of  light  is  unevenly  distributed  over  the  section  of  the  feldspar. 

PLAGIOCLASE. 

The  phenocrysts  of  striated  feldspar  have  -much  the  same  general 
characters  as  those  of  sanidine,  but  they  are  usually  smaller  and  exhiljit  a 
great  number  of  thin  striaj,  or  lamella?,  twinned  after  the  albite  law,  rarely 
after  that  of  pericline.  They  are  sometimes  in  Carlsbad  twins.  The  optical 
behavior  indicates  that  they  are  oligoclase  or  albite.  In  a  few  instances 
the  symmetrical  extinction  angles  indicate  labradorite.  Such  crystals  yield 
square  sections.  They  carry  the  same  kinds  of  inclusions  as  sanidine,  but 
often  a  greater  amount  of  them.  Small  rectangular  glass  inclusions  occur 
in  abundance  in  some  plagioclases,  while  others  are  honeycombed  with 
inclusions  of  groundmass  which  equal  the  feldspar  in  amount.  Inclusions 
of  auo-ite  are  more  common  than  in  sanidine,  and  less  frequently  those  of 
magnetite,  zircon,  and  apatite.  Plagioclase  is  often  inclosed  by  sanidine, 
as  already  remarked,  which  sometimes  only  forms  a  thin  shell  around  a 
portion  of  the  plagioclase  crystal,  and  may  take  part  in  the  microgi-aphic 
stracture  of  the  groundmass.  iBut  the  plagioclase  in  these  rhyolites  has  not 
been  observed  to  enter  into  micrographic  intergrowth  with  or  to  inclose 
quartz. 

PYROXENE. 

The  ferromagnesian  pltenocrysts  in  all  of  the  rhyolite  of  this  region 
belong  to  the  pyroxene  group,  with  the  exception  of  a  small  amount  of 
microscopic  biotite  in  the  rhyolite  of  Glade  Creek.     Fayalite  is  a  product 

'  Miigge,  0.,Petrographische  Untersuchungen  an  Gesteineu  von  deu  Azoren:  Neuee  Jahrbucli 
fur  Mineral.,  1883,  vol.  2,  pp.  189-244  (p.  204). 


400     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  the  final  consolidation  of  the  magma,  and  is  not  included  among  the 
jjhenociysts.  In  most  instances  the  pyroxene  is  augite,  which  occurs  in 
almost  all  of  the  thin  sections  examined,  but  is  present  in  variable  amounts. 
Like  the  other  phenocrysts,  it  is  sometimes  idiomorphic,  with  the  crystal 
form  usual  to  its  occurrence  in  similar  rocks,  or  it  may  be  partially  rounded, 
or  in  fragments.  Tlie  crystals  range  from  3  mm,  long  to  microscopic  ones. 
The  color  is  green,  which  is  strong  grass  green  in  moderately  thick  sections, 
and  pale  green  in  thin  ones.  Its  substance  is  very  pure,  with  compara- 
tively few  inclusions,  which  are  for  the  most  part  magnetite  or  ilmenite, 
zircon,  and  pseudobrookite,  and  rarely  apatite.  In  one  instance  augite 
incloses  a  nearly  idiomorphic  crystal  of  quartz  which  is  almost  the  same 
size.  In  this  particular  case  the  augite  is  the  younger  of  the  two  min- 
erals; it  is  the  only  case  in  the  315  thin  sections  in  which  phenocrysts  of 
these  two  minerals  may  be  observed  in  conjunction.  The  augite  is  usually 
associated  with  crystals  of  iron  oxides,  zircon,  and  pseudobrookite. 

In  many  cases  the  augite  has  a  narrow  opaque  border,  or  a  transparent 
red  one,  undoubtedly  composed  of  iron  oxide.  Rarely  there  is  a  narrow 
border  of  brown  glass  surrounding  the  augite,  when  the  glass  of  the  ground- 
mass  is  colorless.  Occasionall)^  fragments  of  augite  show  that  the  crystal 
was  inclosed  in  the  black  shell  before  it  was  broken — that  is,  the  corrosion 
took  place  before  fracturing.  The  iroii  oxide  sometimes  penetrates  cracks 
in  the  augite.  In  one  crystal  there  is  a  set  of  secondary  inclusions  like 
delicate  needles,  which  are  arranged  along  cracks  and  lie  parallel  to  one 
another  and  to  the  orthoaxis  of  the  crystal.  In  rhyolite  that  has  been 
subjected  to  the  action  of  thermal  waters  the  augite  has  been  completely 
decomposed  and  replaced  by  secondary  minerals. 

In  a  few  cases  an  orthorhombic  pyroxene  is  also  present  in  small 
amount.  It  is  faintly  pleochroic,  and  appears  to  be  hypersthene,  though 
possibly  enstatite.  It  seldom  occurs  independently  of  augite,  and  is  gener- 
ally inclosed  within  the  latter  with  parallel  orientation. 

MAGNETITE   AND   TITANIFEROTJS   IRON   OXIDE. 

Magnetite  and  titaniferous  iron  oxide  are  prominent  porphyritical 
constituents  of  these  rhyolites,  although  they  are  usually  of  microscopic 
proportions — that  is,  they  stand  out  plainly  as  relatively  large  crystals  in 
distinction  to  those  forming  the  gromidmass,  and  show  by  their  mode  of 


ZIRCON  AND  rSEUDOBROOKITE.  401 

occuiTeuce  and  groupinj^  that  they  belong  to  the  jihase  of  crystalHzation 
in  whicli  the  hirger  phenocrysts  were  fonned.  The  same  may  be  said  of 
zircon,  pseudobrookite,  a})atite,  and  alhvnite. 

In  most  cases  it  is  not  possible  to  determine  whether  the  iron  mineral 
present  is  magnetite  or  ilmenite.  Cleavage  lines  intersecting  at  60°  are 
recognized  in  ])artially  decomposed  crystals,  which  occur  in  more  or  lesfe 
altered  rhyolite  from  the  west  wall  of  the  Grand  Canyon  of  the  Yellow- 
stone (2090,  2102).  In  other  cases  of  altered  rhyolite  the  iron  oxide  has 
beer,  converted  into  a  white  opaque  substance,  indicating  the  presence  of 
titanic  oxide,  whose  general  presence  in  the  rhyolite  of  this  region  is  shown 
by  the  widespread  occurrence  of  pseudobrookite,  as  well  as  by  its  chemical 
determination.  In  most  cases  the  iron  mineral  is  perfectly  fresh.  Its  form 
is  often  crystallographic,  but  quite  as  often  irregular.  Some  crystals  are 
definitely  magnetite;  others  are  not  determinable  by  their  outline,  but 
differences  of  luster  are  sometimes  recognized.  It  occurs  in  isolated  o-rains 
from  0.15  mm.  in  diameter  to  smaller,  and  also  in  groups  of  several  grains.  It 
is  generally  attached  to  augite  crystals,  which  sometimes  inclose  as  many 
as  nine  grains  in  one  section. 


ZIRCON. 


Zircon  is  almost  universally  present  in  well-developed  microscopic 
crystals,  which  are  stout  prisms  with  very  simple  forms,  often  consisting  of 
the  unit  prism  and  pyramid,  with  corners  truncated  by  the  ditetragonal 
pyramid  (311).  The  zircons  are  colorless,  with  few  inclusions;  occasionally 
irregularly  shaped  inclusions  and  prismatic  ones  are  numerous.  The  amount 
of  zircon  present  in  different  varieties  of  the  rock  varies  from  none  to 
relative  abundance,  one  large  grain  of  magnetite  having  as  many  as  ten 
crystals  of  zircon  attached  to  or  included  in  it. 

PSEUDOBROOKITE. 

Pseudobrookite  is  almost  as  constant  an  accessory  ingredient  of  these 
rhyolites  as  zircon.  It  is  not  quite  so  abundant,  but  attains  larger  dimen- 
sions, in  one  case  reaching  a  length  of  0.09  mm.,  but  usually  being  much 
smaller.  Its  determination  rests  wholly  on  its  optical  characters.  It 
generally  occurs  in  idiomorphic  crystals,  whose  habit  differs  somewhat. 
The  more  common  forms  are  short  stout  prisms  with  pyramidal  termina- 

MON  XXXII,  PT  II 26 


402  GEOLOGY  OF  THE  YELLOWSTO^fE  NATIONAL  PAEK. 

tions,  or  minute  crystal  grains;  also  long  slender  prisms,  which  are  flat  and 
lathlike.  In  a  few  cases  it  occurs  in  thin  prismatic  plates,  not  wholly 
reo-ular  in  outline.  It  is  evidentl}'  a  biaxial,  orthorhonibic  mineral  with 
high  index  of  refraction  and  brilliant  luster.  Its  color  varies  from  fox  red 
to  reddish  brown  and  opaque,  and  there  is  usualh'  complete  absorption 
parallel  to  the  longer  axis  of  the  prism.  Cleavage  or  inclusions  were  not 
observed.  It  is  closely  associated  with  iron  oxide  and  zircon,  being- 
attached  in  many  cases  to  the  former.     But  it  often  occurs  isolated. 

ALLANITE   AND   APATITE. 

Allanite  occurs  in  only  one  of  the  specimens  of  rhyolite  examined — that 
(2059)  from  the  head  of  Sour  Creek.  Three  or  four  crystals  of  it  are  formed 
in  two  thin  sections  of  this  rock.  They  are  considerabh^  larger  than  the 
crystals  of  pseudobrookite,  but  resemble  them  in  exhibiting  an  almost  total 
absorption.     The  color  is  chestnut  to  olive  brown. 

Apatite  is  present  in  very  small  amount  and  is  only  occasionally 
observed.     It  forms  minute  hexagonal  prisms. 

GROUNDMASS. 

In  studying  the  different  phases  of  groundmass  in  the  various  modifi- 
cations of  this  rhyolite,  we  should  commence  with  those  exhibiting  the  least 
degree  of  crystallization  and  proceed  to  those  exhibiting  the  greatest.  No 
other  rocks  possess  the  variability  of  microstructure  in  their  groundmasses 
that  is  found  to  exist  in  those  of  the  acid  lavas,  especially  the  most  siliceous. 
The  microstructure  of  the  groundmass  of  rhyolites  not  only  varies  in  differ- 
ent parts  of  the  same  rock  body  to  a  very  considerable  extent,  but  in  an  area 
of  a  few  square  millimeters  the  variations  are  strongly  marked,  glassy  and 
holocrystalline  structures  occurring  together  in  some  instances  within  the 
field  of  vision  of  a  microscope.  This  variability  arises  from  a  lack  of  homo- 
geneity in  the  constitution  of  the  most  highly  siliceous  magmas  at  the 
moment  of  their  eruption  upon  the  surface  of  the  earth.  The  demonstration 
of  this  connection  was  furnished  by  the  earlier  studies^  on  the  rocks  now 
being  described,  and  will  be  reviewed  in  the  general  discussion  of  these 

rocks. 

In  a  systematic  description  of  all  the  modifications  of  structure  exhibited 

'Obsidian  Cliff,  Yellowatoue  National  Park:  Seventh  Ann.  Kept.  U.  S.  Geol.  Survey,  1888,  p.  286. 


KHYOLITIO  GLASSES  NEAKLY  FKEE  FROM  MIGROLITES.       403 

by  the  rliyolites  of  the  Yellowstone  National  Park,  Ave  shall  consider,  first, 
those  most  nearl}'  amorphous — that  is,  almost  completely  <i-lassy;  and  sul)- 
secpiently,  those  with  more  and  more  crystallized  mineral  constituents,  or 
those  in  which  the  mineral  crystals  have  attained  their  most  advanced 
development.  This  method  of  procedure  A\'ill  separate  for  the  time  neigh- 
boring- portions  of  one  rock  whose  connection  can  be  pointed  out  subse- 
quently, but  it  has  the  advantage  of  allowing  a  comparison  of  all  similar 
structures  and  the  selection  of  those  which  offer  the  best  illustration  of  the 
probable  explanjitiou  of  the  cause  or  origin  of  the  structure  under  discussion. 

GLASSES   FREE   OR   ALMOST   FREE   FROM   MICROLITES. 

Glasses  absolutely  free  from  microlitic  crystallization  are  seldom  met 
with,  but  man}'  of  them  have  so  few  microhtes  that  they  may  be  classed 
with  the  former  as  glasses  free  or  almost  free  from  microlites.  Such  glasses 
may  be  colorless  in  thin  section,  or  colored  to  a  greater  or  less  degree. 
The  colorless  glasses  free  from  microlites  are  in  almost  every  instance  highly 
pumiceous,  so  that  the  glass  solidified  in  thin  rods  or  films,  and  it  is  found 
that  those  portions  of  the  mass  not  so  highly  inflated  carry  abundant  micro- 
lites. It  must  thei'efore  have  been  the  sudden  expansion  of  the  inclosed 
vapors,  and  the  consequent  chilling  of  the  magma,  that  prevented  the 
microlitic  minerals  from  crystallizing  before  the  magma  solidified.  In  such 
cases  it  is  evident  that  the  magma  reached  the  surface  of  the  earth  in  a 
wholly  amorphous  condition,  except  for  the  phenocrysts,  which  may  or 
may  not  have  been  developed.  In  one  instance  a  pumiceous  glass  is  full  of 
microlites,  which  must  have  crystallized  before  the  rock  became  pumiceous. 

Colorless  pumice  free  from  phenocrysts  forms  the  upper  portion  of  the 
obsidian  flow  on  the  plateau  southeast  of  Obsidian  Cliff.  It  is  slightly 
microlitic.  Pumices  free  from  microlites,  but  with  more  or  less  phenocrysts, 
occur  on  Madison  Plateau  south  of  Madison  Canyon,  on  the  edge  of  the 
plateau  west  of  Yellowstone  River  near  the  mouth  of  Otter  Creek,  on  the 
west  shore  of  Yellowstone  Lake  south  of  Bridge  Creek  Bay,  and  in  other 
localities.  The  gas  cavities  in  these  pumices  are  sometimes  microscopic, 
and  are  generally  elongated,  spindle-shaped  or  drawn  out  to  long  thin  tubes. 
Occasionally  they  appear  to  contain  a  small  amount  of  liquid.  In  many 
cases  the  cavities  are  comparatively  large,  as  in  ordinary  pumice.  In  some 
instances  it  is  evident,  from  the  confusedly  twisted  and  curved  arrangement 


404     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

of  the  glass  fibers  and  films,  that  the  inflated  glass  mass  settled  back  upon 
itself,  or  collapsed,  after  the  escape  of  much  of  the  gas.  This  is  possible 
from  the  fact  that  after  a  magma  has  been  rendered  pumiceous  it  ma}- 
still  remain  viscous  before  its  temperature  is  reduced  to  the  point  of  solidi- 
fication. It  has  been  observed  during  the  artificial  fusion  of  obsidian  that 
rhyolitic  pumice  will  retain  its  expanded  form  at  a  temperature  at  which  it 
is  viscous  enougli  to  be  easily  compressed  or  penetrated  by  a  rigid  body. 
Hence,  in  a  moving  stream  of  rhyolitic  lava,  portions  which  have  been 
inflated  to  pumice  may  be  forced  while  yet  plastic  into  more  compact 
masses  by  the  movement  of  the  lava,  and  they  ma}^  be  expected  to  exhibit 
some  indications  of  their  former  pumiceous  condition.  When  we  remember 
the  enormous  extent  of  many  of  the  streams  of  rhyolite  in  this  region,  we 
may  easily  imagine  the  formation  of  pumice  over  the  surface  of  an  intensely 
heated  area  of  lava,  thus  permitting  of  its  subsequent  welding. 

An  example  of  collapsed  pumice  is  found  in  that  which  occurs  on  the 
plateau  forming  the  continental  divide  southwest  of  Madison  Lake  (1942). 
It  is  a  colorless  glass  free  from  microlites  and  with  phenocrysts.  It  is 
partly  pumiceous,  but  tlie  bubbles  are  small,  elongated,  and  greatly  twisted, 
as  are  also  the  glass  fibers  and  films,  which  curve  about  one  another  in 
endless  complication.  Their  form  is  indicated  by  faint  lines,  which  may 
mark  films  of  gas,  or  may  be  the  boundary  between  glasses  ^^'ith  slightly 
diff'erent  refraction  and  color.  Parts  of  the  glass  are  faintly  yellowish,  and 
most  of  it  exhibits  the  double  refraction  common  to  perlitic  glass.  A  perlitic 
structure  is  present  in  portions  of  the  glass.  The  direction  of  \dbration 
of  the  slowest-traveling  ray  is  normal  to  the  perlitic  cracks  and  to  the 
surface  of  the  fibers,  which  should  also  be  the  direction  of  the  least  stress, 
the  fracture  having  relieved  it.  It  is  observed  in  some  cases  that  there  is 
a  distinct  margin  to  the  cross  sections  of  some  of  the  glass  rods,  and  this 
maro-in  has  a  faint  color  and  diff'erent  refraction  from  that  of  the  center. 
It  is  more  strongly  refracting  parallel  to  the  direction  of  vibration  of  the 
slowest  ray,  normal  to  the  surface  or  boundary  of  the  rod.  The  central  part 
of  the  rods  and  perlitic  masses  exhibits  an  opposite  state  of  strain.  Thus, 
within  the  'glass  rod  the  direction  of  vibration  of  the  slowest  ray  coincides 
with  that  of  the  axis  of  the  rod — that  is,  the  direction  in  which  it  was 
stretched.  But  in  the  marginal  portion  the  direction  of  vibration  of  the 
slowest  ray  is  normal  to  the  first;  it  must  therefore  be  due  to  some  other 


COLORED  RHYOLITIG  GLASSES.  405 

cause,  as  alreaay  intimated.  Thi.s  double  condition  of  refraction  does  not 
appear  on  thin  rods  taken  fron\  a  parallelly  fibrous  pumice.  There  is  only 
the  adjustnient  of  refraction  produced  by  the  stretching. 

Colored  glasses  free  from  microlites  are  rather  more  frequent  among 
the  rhyolites  of  the  Yellowstone  Park  than  colorless  ones.     They  are  largely 
pumiceous,  or  are  collapsed  pumice.     The  colors  in  thin  section  are  dark 
seal  brown  to  yellow,  less  frequently  orange  and  red.     In  most  cases  the 
coloring  matter  can  not  be  resolved  into  discrete  particles,  but  appears  to 
have  been  in  solution.     It  seldom  happens  that  the  glass  is  of  uniform  color 
throughout  the  extent  of  a  rock  section.     It  is  usuallj^  variegated,  brown 
and  yellow,  and  either  or  both  of  these  occur  with  colorless  glass.     Brown 
glass  pumice  occurs  on  the  west  shore  of  Yellowstone  Lake  and  elsewhere. 
In  it  the  brown  color  grades  into  yellow  along  the  margin  of  gas  cavities 
and    along  the  surface  of  rods;  in   some    places  the  contrast   is    sharply 
marked.     It  is  not  due  to  a  thinning  of  the  glass.     The  color  is  different  in 
kind,  and  its  distribution  is  very  similar  to  that  of  the  interference  phe- 
nomena in  the  colorless  pumice.     In  the  brown  glass,  however,  no  double 
refraction  is  noticeable.     A  change  from  brown  to  colorless  takes  place  in 
the  same  manner,  and  in  some  cases  the  transition  is  from  brown  to  yellow, 
and  then  to  colorless.     It  is  evident  that  in  these  instances  the  change  of 
color  is  connected  with    the  inflation  of  the  glass  into  pumice.     In  other 
cases  a  cause  is  not  so  apparent.     But  the  fact  is  obvious  that  the  change 
has  been  from  darker  to  lighter  color,  from  Ijrown  to  colorless.     It  is  often 
observed  that  the  inclusions  in  phenocrysts  are  brown,  while  the  ground- 
mass  surrounding  them  is  lighter  colored  or  colorless.     In  one  case  (1909)  the 
glass  inclusions-  are  brown,  and  the  bays  of  groundmass  in  the  phenocrysts 
are  brown  and  yellow,  the  groundmass  as  a  whole  being  yellow,  with  some 
patches  of.  brown  scattered  through  it.     These  appear  to  be  remnants  of  a 
once  brown  glass  almost  wholly  changed  to  yellow.     A  collapsed  brown 
and  yellow  glass  pumice  is  shown  in  PI.  LI,  fig.  1.     It  carries  phenocrysts 
of  quartz  and  sanidine,  with  glass  inclusions  and  "bays."     In  a  few  cases 
colorless  glass  rods  are  seen  to  have  yellow  margins,  as  though  the  change 
had  been  from  colorless  to  yellow. 

In  numerous  cases  a  pumiceous  character  is  entirely  wanting.  The 
mass  is  compact  glass,  but  it  consists  of  irregularly  shaped  streaks  and 
patches  of  different  color.     These  twist  and  curve  about  one  another  and 


406     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

appear  like  a  perfectly  welded  mass  of  strips  or  ribbons  and  iri'egular  frag- 
ments of  variously  colored  glass.  In  some  cases  their  shape  closely 
resembles  that  of  fragments  of  pumice  pressed  together  and  welded  (PL  L, 
figs.  1,  2,  and  3).  In  others  it  .appears  as  though  such  fragments  had  been 
drawn  out  and  twisted  by  a  movement  of  the  mass  (PL  LI,  fig.  2). 
Undoubtedly  this  has  been  the  case,  but  it  is  doubtful  whether  all  the 
streaked  and  variegated  glasses  have  passed  through  the  process  of  inflation, 
collapse,  and  welding  witli  subsequent  flow.  However,  the  distinctly  out- 
lined and  strongly  contrasted  streaks  and  ribbons  of  variously  colored 
glass,  are  with  difficulty  explained  in  any  other  manner.  Another  possible 
explanation  will  be  given  in  connection  with  the  development  of  microlites. 
This  streaked  arrangement  of  colored  glasses  has  been  called  "  eutaxitic" 
structure. 

GLOBULITIC   GLASS. 

The  colored  glasses  are  in  many  cases  crowded  with  minute  dots  or 
jjarticles,  which  are  the  pigment,  the  glass  itself  being  colorless.  Such 
glasses  are  said  to  be  globulitic.  The  connection  between  the  globulitic 
and  colored  glasses  is  well  shown  in  certain  banded  and  streaked  colorless 
and  orange  glasses,  as  well  as  in  brown,  yellow,  and  colorless  ones.  In  the 
former  it  is  observed  that  the  orange-colored  bands  in  j^laces  become 
globulitic  with  minute  orange  or  3rellow  particles.  As  these  particles 
become  more  distinct  and  larger  they  are  farther  apart  and  are  usually 
darker  colored,  in  extreme  cases  becoming  oj)aque  black  grains,  dissemi- 
nated through  colorless  glass.  Brown  glass  in  like  manner  passes  into 
colorless  glass  with  brown  globulites,  which  may  be  opaque  in  the  extreme 
forms.  Such  globulitic  glass  may  appear  bluish  by  transmitted  light  when 
not  in  focus,  owing  to  dispersion  of  the  light.  It  is  evident  that  the  glob- 
ulitic pigment  is  a  segregation,  and  eventually  a  crystallization,  of  the 
coloring  matter,  which  sometimes  permeates  the  glass  as  though  in  solution. 
There  is  a  distinct  contraction  or  condensation  of  the  coloring  material,  for 
bands  which  grade  from  colored  glass  to  globulitic,  and  into  those  with 
crvstalline  grains,  become  thinner  and  narrower,  often  resulting  in  a  film  of 
particles,  or  in  a  contracted  belt  noticeably  smaller  than  the  undiff'erentiated 
belt.  In  some  cases  of  welded  pumice  of  variously  colored  glass  the 
general  color  is  yellow  or  orange  (2058).  Some  fragments  are  colorless  at 
the  center,   with  yellow  margins,  while   the    larger  fragments   are    either 


U.  8.  QEOLOQICAL    SURVEY 


MONOGRAPH    XXXll     PART    II     PL.   L 


fA)  ,   32 


(B)  .    3  2 


(Cj  K  47 


fDj  X   32 


PHOTOMICROGRAPHS    OF  RHYOLITIC    GLASSES 


THE  HELIOTYPE  PRINTING  CO..   BOSTON 


U.  8.  OEOLOOICAL    SURVEY 


MONOGRAPH    XXXM     PART    II     PL.  LI 


(A)x   15 


<B)%   15 


(C)%   15 


( D)  t    18 


PHOTOMICROGRAPHS    OF  RHYOLITIC    GLASSES 


THE  HELrOTVPE  PRtNTrNG  CO.,  BOSTON 


GLOBULITIC  RIIYOLITIC  GLASSES.  407 

yellow,  grailiug  in  places  into  ylolnilitic  brown  surrounded  by  a  colorless 
zone  with  a  yellow  niarg-in,  or  the  central  portion  is  colorless  with  swarms 
of  minute  grains,  the  margin  being  as  in  other  cases.  The  minute  grains 
are  bright  yellow  in  incident  light,  and  almost  opaque  by  transmitted  light. 
With  high  magnifying  lens  they  appear  to  be  partly  transparent,  but  no 
double  refraction  is  noticeable. 

In  other  cases  these  globulites  are  represented  by  microlites,  many  of 
which  are  opaque  grains,  apparently  magnetite,  together  with  others  which 
will  be  described.  The  transition  of  yellow  and  brown  colored  glass  streaks 
into  globulites  and  microlites  is  well  shown  in  the  colored  obsidian  from 
Obsidian  Cliff,  represented  by  iig.  1  of  PI.  XVI  in  the  Seventh  Annual 
Report  of  the  United  States  Geological  Survey,  in  which  the  cnrved  and 
contorted  bands  of  color  and  streams  of  trichites  produce  grotesque  shapes 
in  thin  section,  like  imitations  of  various  forms  of  organic  nature.  From 
this  it  appears  that  the  tones  of  yellow,  orange,  red,  brown,  and  black  are 
due  to  different  states  of  oxidation  of  the  iron  in  the  magma,  which  may  be 
cr3'stallized  out  as  magnetite  and  sometimes  subsequently  oxidized  to  the 
ferric  state,  as  shown  by  the  red  color  of  many  trichites  in  incident  light, 
or  the  iron  oxide  may  be  disseminated  in  minute  particles  whose  precise 
character  is  not  determinable,  or  the  coloring  matter  ma}^  be  in  solution. 
In  some  parts  of  Obsidian  Cliff  the  red  and  black  streaked  glass  is  brecci- 
ated,  the  angular  fragments  being  welded  into  a  compact  mass,  as  shown 
in  PI.  LI,  tig.  3.  An  extremely  delicate  banding  is  shown  in  PI.  L,  fig.  4, 
caused  by  alternating  streaks  of  colorless  and  red  and  yellow  globulitic 
and  tricliitic  glass.  The  folding  of  the  streaks  is  well  shown.  They  pass 
through  faint  spherulitic  growths. 

A  frequent  microstructure  is  one  produced  by  thin  films  of  globulites 
and  particles  like  dust,  which  appear  to  be  scattered  in  planes  through 
colorless  glass.  The  films  curve  and  fold  about  one  another  in  the  most 
intricate  manner,  producing  the  effect  of  thin  veils.  This  structure  appears 
to  have  resulted  from  the  welding  together  of  fragments  of  glass,  as  in  the 
case  of  certain  colored  glasses  already  described.  This  veil  structure  is 
otten  retained  after  the  whole  mass  has  become  crystalline,  and  serves  to 
indicate  one  of  the  phases  through  which  the  magma  has  passed. 


408  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

MICROLITIC   GLASS. 

Most  of  the  rhyolitic  glasses  in  the  Yellowstone  Park  are  microlitic. 
The  microlites  may  be  uniformly  scattered  through  the  glass,  or  they  may 
be  abundant  in  alternating  layers  or  bauds,  or  they  may  occin-  irregularly 
in  patches  and  streaks  with  colored  and  globulitic  glass,  as  already  mentioned 
They  are  usually  distributed  uniformly  in  massive  obsidian,  but  often 
exhibit  a  somewhat  parallel  arrangement,  or,  more  properly,  a  slight  varia- 
bility in  abundance  in  parallel  planes,  which  mark  the  planes  of  flow  or 
movement  within  the  magma.  This  may  be  seen  in  PI.  LV,  fig.  "1.  This 
variability  is  more  pronounced  in  portions  of  the  glass  which  are  partly 
vesicular  or  pumiceous — that  is,  where  dense  microlitic  obsidian  passes  into 
pumiceous  nonmicrolitic  glass,  as  in  the  upper  portion  of  the  lava  near 
Obsidian  Cliff  and  elsewhere. 

The  character  of  the  microlites  may  l)e  surmised  from  their  shape  and 
color  in  some  cases,  and  from  their  optical  behavior  in  others,  or  b}'  tracing 
similar  forms  from  the  minutest  to  those  large  enough  to  be  recognized. 
In  this  way  it  is  found  that  they  are  undoubtedly  magnetite,  augite,  feld- 
spar, and  quartz,  and  rarel}'  hornblende  and  hematite,  and  probably  pseu- 
dobrookite.  Magnetite  occurs  in  minute  crystals  and  grains,  isolated  or 
attached  to  prisms  and  needles  of  augite.  The  opaque  hair-like  trichites, 
straight  and  curved,  in  some  cases  are  separated  into  rows  of  opaque  grains 
resembling  magnetite.  In  other  cases  they  form  threads  on  which  are 
strung  transparent  rhombic  plate-like  microlites,  as  in  the  illustration,  PI. 
LII,  fig.  6.     Such  microlites  have  a  pale-greenish  tinge. 

Feldspar  microlites  are  sometimes  thin  plates  parallel  to  the  clinopina- 
coid,  with  the  outline  formed  by  basal  plane  and  prism  or  orthopinacoid. 
They  are  often  in  Carlsbad  twins,  in  juxtaposition  and  cruciform.  These 
are  probably  orthoclase.  In  some  less  siliceous  glasses  the  feldspar  crystals 
are  tabular  and  rectangular  with  projecting  corners.  With  these  are  asso- 
ciated lath-shaped  crystals,  forked  or  fibrous  at  the  ends,  which  are  probably 
oligoclase. 

Quartz  occurs  in  minute  hexagonal  pyramids,  whose  form  and  double 
refraction  can  be  distinctly  recognized.  They  range  in  size  from  0.002  to 
0.015  mm.  in  diameter.  They  may  easily  escape  detection,  and  were  over- 
looked in  the  obsidian  of  Obsidian  Cliff'  when  the  first  study  of  it  was 
made.     They  are  not  found  in  all  the  rhyolitic  glasses  in  the  Yellowstone 


MICKOLITIC  RIIYOLITIC  GLASSES.  409 

Park  which  carry  niicrolites.  In  parts  of  the  obsidian  of  Obsidian  Cliff 
they  occur  with  feldspar  niicrolites  and  slightly  larger  niicrographic 
intergrowths  of  quartz  and  feldspar  in  banded  swarrns,  alternating  layers 
being  nem-ly  free  from  microlites.  It  was  the  presence  of  the  microscopic 
niicrographic  intergrowths  in  association  with  feldspar  microlites  which 
led  the  present  writer  to  infer  the  presence  of  quartz  microlites,  although 
quartz  had  not  been  observed  in  such  form  before  that  time.'  If  quartz 
crystallized  synchronously  in  conjunction  with  feldspar  to  form  such 
micropraphic  microlites,  and  if  the  feldspar  also  crystallized  alone,  why 
had  not  quartz  also  crystallized  by  itself  at  the  same  time!  After  a  very 
short  search  the  quartz  microlites  were- found  in  recognizable  individuals. 

In  the  colored  glasses,  in  some  instances,  a  few  dark-colored  microlitic 
prisms  and  grains  occur  surrounded  by  a  light-colored  zone  or  "  halo," 
which  indicates  the  concentration  of  the  coloring  matter  in  the  microlite. 
In  parts  of  the  pumice  at  Obsidian  Cliff  there  are  microlitic  grains,  prob- 
ably augite,  each  of  which  is  surrounded  by  a  minute  sphere  of  colorless 
substance,  about  0.023  mm.  in  diameter,  with  a  higher  index  of  refraction 
than  the  surrounding  glass.  In  another  pumice  (1909)  the  outline  of  the 
colorless  bodies  is  seen  to  be  jagged,  as  though  made  up  of  crystal  indi- 
viduals, and  in  some  cases  they  project  beyond  the  glass  walls  of  vesicular 
cavities.  They  are  noticeably  doubly  refracting,  and  may  be  incipient 
spherulitic  growths. 

The  various  kinds  of  microlites  are  not  always  present  in  like  amounts. 
In  many  cases  the  glass  appears  to  swarm  with  trichites  and  microlites  of 
augite,  in  short  prisms  and  grains.  In  some  cases  the  trichites  seem  to  be 
magnetite;  in  others  they  are  augitic  needles.  In  a  compact  glass  (1941) 
from  the  plateau  south  of  Madison  Lake,  which  is  colorless  in  thin  section, 
there  are  long,  curved,  opaque  trichites  which  are  grouped  about  thin  layers 
of  opaque  grains,  the  trichites  themselves  in  many  cases  consisting  of 
opaque  grains,  as  though  the  trichite  had  been  disjointed  by  shrinking. 
With  these  are  very  few  other  microlites. 

In  some  of  the  obsidian  at  Obsidian  Cliff  (2210,  2241,  2242)  the  micro- 
lites are  mostly  feldspar  and  quartz  with  needles  of  augite  and  a  few  mag- 

'  The  observation  by  Dr.  Kiich  of  quartz  microlites  in  the  dacitic  glasses  of  Colombia  was  not 
known  to  the  writer  at  the  time  this  investigation  was  made.  W.  Reiss  uud  A.  Stiibel,  Reiseu  in  Siid- 
Amerika.  Geologische  Studien  in  der  Republik  Colombia.  I.  Petrologie.  I.  Die  vulkanischen  Ges- 
teine,  bearbeitet  von  Richard  Kiich.     Berlin,  1892. 


410     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

iietite  grains,  and  a  few  needles  which  are  possibly  pseudobrookite.  In  an 
obsidian  from  the  plateau  northeast  of  Obsidian  Cliff,  which  carries  many- 
shrunken  hollow  spherulites  (2216),  there  are  scattered  microlites  of  great 
beauty.  The  largest  are  iliicrographic  intergrowths  of  quartz  and  feld- 
spar which  sink  to  the  minutest  dimensions;  also  tabular  feldspar,  simple 
and  in  Carlsbad  twins^  as  well  as  some  rectangular  forms  with  horned 
corners;  pyramidal  quartz,  one  of  the  larger  individuals  containing  a  glass 
inclusion;  hexagonal  plates  of  hematite  or  ilmenite,  opaque,  with  metallic 
luster;  prisms  of  augite,  some  knobbed  at  the  ends,  like  bones;  and  occa- 
sionfil  dark-green  prisms  of  hornblende. 

In  the  same  neighborhood  is  obsidian  with  duller  luster  and  a.  greenish 
tinge,  which  is  less  siliceous  and  approaches  dacite  in  chemical  composition. 
It  consists  of  compact  colorless  glass  (2164)  with  a  multitude  of  microlites. 
Many  are  augite  in  prisms,  many  are  feldspar,  while  some  are  magnetite. 
The  feldspar  microlites  are  mostly  tufted  or  horned  and  some  have  multiple 
twinning.  A  very  few  are  in  Cai-lsbad  twins.  There  are  some  larger 
microscopic  crystals  of  feldspar  and  augite,  but  no  microscopic  phenocrysts. 
There  are  no  inicrolites  of  quartz  and  no  tricliites.  Another  part  of  this 
obsidian  is  still  richer  in  augite,  with  smaller  feldspar  needles  and  magnetite 
grains.     The  microstructure  is  almost  andesitic. 

In  some  of  the  compact,  microlitic  glasses  perlitic  stracture  is  highly 
developed,  as  shown  in  PI.  LI,  fig.  4.  Its  character  is  too  well  known  to 
need  description  in  this  place. 

FORMS  OF  GROWTH   OF  MICROSCOPIC  CRYSTALS. 

There  is  a  marked  tendency  exhibited  by  the  microscopic  crystals  in 
rhyolitic  magmas  to  form  intergrowths  and  also  compound  groups  of  crys- 
tals. The  well-known  graphic  intergrowth  of  orthoclase  and  quartz  is  one 
of  the  most  characteristic.  Microscopic  examples  are  of  frequent  occur- 
rence and  have  been  described  in  the  paper  on  Obsidian  Cliff.'  They 
can  be  traced  from  megascopic  groups  in  which  the  nature  of  the  compo- 
nent minerals  can  be  determined  to  micr6scopic  ones  of  the  minutest 
dimensions  in  which  only  the  general  form,  crystalline  structure,  and 
general  optical  behavior  can  be  recognized.  Such  groups  are  seen  in  thin 
section  to  consist  of  several  individuals  of  feldspar  intersecting  one  another, 

I  Seventh  Ann.  Rept.  U.  S.  Geol.  Survey,  1888,  pp.  274-276. 


U.   8.   OEOLOOICAL  SURVEY 


MONOORAPH  XXXII      PART   II      PL.   Lll 


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m 


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i 


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A  -^ 


SPHERULITES. 


MigUOURAPHlC  INTEKGROWTHS  IN  KIIYOLITE.  411 

each  individual  having  a  fibrous  structure  in  several  directions,  and  in  places 
a  granuhir  structure.  This  is  shown  in  PI.  Lll,  fig.  3,  which  represents  a 
section  througli  two  individuals  of  feldspar  with  nearly  rectangular  outline. 
The  fibration  lies  almost  perpendicular  to  the  sides  of  the  rectangles.  The 
outline  of  the  rectangles  is  serrated  by  the  projection  of  minute  crystals. 
The  identity  of  such  forms  with  intergrowths  of  quartz  and  feldspar  is 
apparent.  An  illustration  of  a  large  group  is  introduced  for  comparison 
(PI.  LIT,  fig.  5).  It  is  similar  to  the  graphic  structure  associated  with 
phenociysts  in  rhyolitic  pumice,  already  described.  Such  intergrowths 
are  primary  crystallizations  from  the  molten  magma,  and  exhibit  the  idio- 
morphic  outline  of  quartz  or  feldspar  when  large  enough  to  be  recognizable. 

As  the  number  of  feldspars  which  combine  in  a  group  increases,  the 
outline  of  the  cluster  becomes  more  and  more  oval  or  circular  and  the  form 
of  the  feldspar  individuals  is  lost.  An  illustration  is  given  in  PI.  LII,  fig. 
4,  in  which  the  feldspars  wedge  out  toward  the  center,  their  outer  ends 
making  an  almost  continuous  outline.  The  fibration  is  in  wedge-shaped 
sets  and  does  not  radiate  uniformly  from  the  center.  In  this  case  the  extinc- 
tion of  light  between  crossed  nicols  is  quite  irregular,  as  shown  in  the 
illustration.  This  is  due  to  the  variable  orientation  of  the  feldspar  crystals, 
which  have  a  generally  radiate  arrangement,  and  also  to  that  of  the  quartz, 
which  is  more  irregular.  Other  compound  growths  which  are  analogous  in 
structure  and  optical  behavior  to  the  micrograpliic  are  certain  kinds  of 
spherulites  that  occur  in  great  profusion  in  most  of  these  rhyolites.  The 
simplest  and  smallest  of  this  class  of  spherulites  are  minute  colorless 
spheres,  0.2  to  0.05  mm.  in  diameter.  They  have  a  fibrous  structure  notice- 
able in  strongly  convergent  light,  and  exhibit  a  more  or  less  well  defined 
dark  cross  between  crossed  nicols.  The  arms  of  these  crosses  change  their 
shape  and  split  into  branches  near  their  outer  ends  during  the  rotation  of  the 
section  (PI.  LII,  fig.  2;  also  PI.  LIII,  fig.  1). 

In  some  cases  a  colorless  fibrous  margin  surrounds  the  micrograpliic 
groups;  its  character  and  length  of  fiber  correspond  to  those  of  the 
microspherulites  just  described.  From  its  optical  behavior  it  appears  to  be  a 
crystallographic  continuation  of  the  materials  of  the  micrograpliic  kernel. 
These  spherulites  are  often  in  rows  and  layers  (PI.  LIII,  fig.  1),  and  some- 
times their  centers  are  so  close  together  along  straight  lines  that  in  thin 
section  they  produce  the  eff'ect  of  transparent  fibrous  bands  (PI.  LIII, 
fig.  1).     Such  a  band  of  colorless  spherulites  is  shown  in  PI.  LV,  fig.  1.     It 


412  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

traverses  larger  brown  spherulites.  They  are  also  shown  in  bands  of  more 
or  less  isolated  spherulites  within  the  brown  spherulites.  These  spherulites 
are  represented  meg-ascopically  by  minute  dots  arranged  in  lines  on  the 
surface  of  some  obsidian. 

Spherulites  similar  to  these,  but  slightly  larger,  occur  ci'owded  together 
in  bands  or  in  irregular  areas,  in  which  case  the  rock  is  lusterless  and 
lithoidal,  and  is  usually  colored  gray  in  various  shades.  In  thin  section 
the  finely  spherulitic  portions  may  be  crowded  with  trichites  in  the  same 
manner  as  the  surrounding  glass  is.  These  are  more  perfect  as  the  spheru- 
litic sti'uoture  is  more  minute,  and  their  form  and  arrangement  in  fluidal 
lines  are  lost  when  the  spherulites  are  coarser.  In  these  cases  they  are 
sometimes  crowded  out  toward  the  margin  of  the  spherulites,  or  they  may 
be  accumulated  in  radial  lines. 

The  small  spherulites  exhibit  an  extremely  minute  granulation  by 
transmitted  light,  and  appear  brown;  but  by  incident  light  this  is  Avhite, 
evidently  in  consequence  of  the  reflection  of  light  from  innumerable  small 
surfaces  or  cracks.  In  small  spherulites  lying  isolated  in,  and  also  bor- 
dering, areas  of  greater  crystallization  the  centers  of  the  spherulites  are 
granulated  and  brown,  while  the  margins  are  often  colorless  and  trans- 
parent. In  some  cases  the  centers  of  the  spherulites  are  colorless  and  the 
outer  zone  is  brown.  In  such  spherulites  the  fibers  of  the  outer  zone  are 
more  delicate  than  those  at  the  center.  In  these  spherulites  the  direction 
of  vibration  of  the  fastest  ray  (axis  of  greatest  elasticity)  lies  approximately 
parallel  to  the  direction  of  the  radial  fibers.  The  spherulites  bordering 
more  crystalline  areas  in  lithoidal  rhyolite  have  sometimes  continued  their 
crystallization  a  short  distance  into  these  ai'eas,  when  they  exhibit  distinct 
prismatic  rays  that  project  beyond  the  apparent  periphery  of  the  spherule 
and  resemble  the  teeth  of  a  cogwheel.  Sometimes  the  projecting  prisms 
assume  a  comparatively  large  size.  Such  forms  are  represented  by  a  and  h, 
fig.  4.  The  projecting  prisms  have  crystallographic  boundaries  and  extend 
with  uniform  optical  orientation  toward  the  center  of  the  spherulite.  Their 
form  and  optical  behavior  show  them  to  be  crystals  of  orthoclase  elongated 
in  the  direction  of  the  clinoaxis,  with  the  direction  of  vibration  of  the  fastest 
ray  nearly  parallel  to  the  sides  of  the  prism.  The  extinction  angle  varies 
from  0°  to  12°,  being  usually  low.  The  high  limit  of  the  extinction  angle 
in  the  clinodiagonal  zone,  as  well  as  the  chemical  composition  of  the  rock, 


MlCKOGliAPniC  SPHEKULITES. 


413 


and  of  tlie  sphenilite,  since  there  appears  to  be  but  one  variety  of  feldsjjar 
present,  indicates  that  the  orthochise  is  rich  in  soda,  tlie  uiolecuhxr  ratio  of 
the  i)otash  to  the  soda  in  the  rock  being  1  to  1. 

The  projecting  prisms  are  free  from  the  granuhxtiou  which  is  at  the 
center  of  the  spheruHtes.  In  some  instances  this  assumes  a  radiating, 
feather-Uke  stnxcture  which  suggests  the  micrograpliic  iutergrowth  of 
feldspar  and  (piartz.  This  is  undoubtedly  its  true  character,  as  shown  else- 
where; so  the  small  spherulites  are  unquestionably  composed  of  orthoclase 
prisms  elongated  in  the  direction  of  the  cliuoaxis,  which  radiate  from  a 
center,  and  are  intergrown  with  quartz  in  a  micrograpliic  manner.  When 
the  margin  of  pure  feldspar  was  being  crystallized,  the  free  silica  remained 


^M\X\\j1 1]'//' 


^i^ 


Fig.  i — Sections  of  spherulites  with  projecting  prisms  of  orthoclase  and  a  crescent-shaped  belt  free  from  granulation. 


uncrystallized  until  subsequently,  when  it  filled  the  interspherulitic  spaces 
with  tridymite  or  quartz,  according  to  circumstances. 

There  are  instances  in  which  the  clear  zone  of  feldspar  does  not  occiu- 
on  the  margin  of  the  spherulite,  but  forms  a  crescent-shaped  transparent 
belt  within  it  (c  of  fig.  4  above,  and  fig.  2  of  PI.  LIV).  The  optical  behavior 
of  such  spherulites  shows  that  the  feldspar  fibers  or  prisms  are  continuous 
from  center  to  circumference,  and  that  it  is  simply  the  granulated  or  feather- 
like intergrowth  that  was  interrupted.  This  is  in  accord  with  other  signs  of 
a  lack  of  uniformity  of  microstructure  in  these  highly  siliceous  rocks. 

Still  larger  forms  of  this  kind  of  spherulites  are  the  small  megascopic, 
blue-gray  spherulites,  which  are  from  less  than  1  mm.  to  5  mm.  and  rarely 
10  mm.  in  diameter.  In  thin  section  they  have  much  the  same  characters  as 
the  microscopic  ones.  They  are  distinctly  fibrous  in  sections,  the  fibers 
not  all  radiating  from  a  single  point.     They  often  have  a  micrographic 


414     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

group  or  minute  spherulite  at  the  center.  Between  crossed  nicols  the 
dark  arms  seldom  form  a  distinct  cross,  but  split  into  many  arms,  some 
making  an  angle  of  45°  with  the  principal  sections  of  the  nicols  (PI.  LIL, 

fig.  1). 

These  larger  spherulites  are  generally  traversed  by  streams  of  trichites 
and  minute  spherulites  which  continue  the  flow  lines  of  the  rock  through 
the  spherulite  without  change  of  direction  (PI.  LV,  fig.  2).  But  in  some 
cases  these  interpositions  have  been  crowded  into  radial  and  circular  lines 
(PI.  LV,  figs.  3  and  4,  and  PI.  LVI,  fig.  1).  These  produce  the  bands  or 
zones  of  color  in  the  small  .spherulites.  Often  the  trichites  and  grains  are 
red  by  incident  light,  as  though  the  magnetic  oxide  had  been  changed  to 
ferric  oxide,  and  it  is  noticeable  that  the  black  trichites  and  nearly  colorless 
microlites  in  the  glass  as  they  pass  into  spherulites  become  red,  as  though 
they  had  encountered  an  oxidizing  agent  not  active  in  the  surrounding  glass. 

The  shapes  of  spherulitic  growths  are  not  limited  to  spheres,  but  may 
be  hemispheres,  disks,  and  sectors,  or  plume-Hke  (PI.  LVI,  fig.  1),  or  in  a 
brush  like  a  fox's  tail.  They  may  also  appear  in  thin  section  in  the  form 
of  fibrous  l:)ands  or  fringes  with  all  possible  curvatures.  All  the  spherulitic 
growths  just  described  may  be  referred  to  stellate  groups  of  prisms  of 
orthoclase  elongated  parallel  to  the  clinoaxis,  and  intergrown  with  quartz 
whose  orientation  is  not  known  to  be  fixed  with  respect  to  the  feldspar 
prisms. 

There  are  other  kinds  of  spherulitic  structures  in  these  lavas  which 
have  crystallized  in  a  different  manner.  Their  nature  may  be  understood 
from  a  consideration  of  certain  forms  of  microlitic  growth  assumed  by 
orthoclase  in  these  magmas. 

Prisms  or  needles  of  feldspars  sometimes  occur  associated  together  in 
nearly  parallel  groups,  or  in  more  or  less  divergent  ones.  In  some  cases 
they  are  separated  from  one  another  by  glassy  groundmass;  in  other 
cases  by  a  colorless,  almost  isotropic  mineral,  probably  tridymite,  as  will 
be  shown  subsequently.  These  needles  are  straight  or  curved,  and  some- 
times have  a  rough,  jagged  outline,  sometimes  a  smooth  one.  Long  delicate 
feldspar  needles,  the  spaces  between  which  are  filled  with  tridymite,  are 
shown  in  PI.  LVI,  fig.  2.  The  rock  also  carries  dark-brown  spherulites, 
which  are  nearly  opaque  in  the  figure.  The  cross  sections  are  generally 
six-sided  or  i-hombic,  with  the  acute  angle  truncated  by  a  plane  more  largely 


U.   8.   GEOLOOICAL  SURVEY 


MONOGRAPH  XXXII       PART  II      PL.    Llll 


Fig    I.  SPHERULITES,     Fig.  2.   FELDSPAR   NEEDLES. 


U.  S.  OEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.   LIV 


rAj  X  27 


(  SJ  ,   46 


(Cj  X  50 


rDjx   ^2 


PHOTOMICROGRAPHS    OF    MICROGRAPHIC    PHENOGRYSTS    AND    SPHERULITES 


THE  HELIOTVPE  PRINTING  CO.,  BOSTON 


U.  S.  GEOLOGICAL    SURVEY 


MONOGRAPH    XXXII     PART    M     PL,   LV 


^.^ 


(B>  ,    12 


(C)  X    12 


(D)  %    12 


PHOTOMICROGRAPHS    OF  SPHERULITIC    STRUCTURES 


THE  HetlOTYPE   PRINTING  CO.,  BOSTON 


BUANCniNG  FELDSPAR  MIGR0L1TE8.  415 

developed  than  tliu  (»tlior.s.  In  scime  cases  the  sections  are  twinned  parallel 
to  the  broad  plane.  In  the  rhombic  sections  the  extinction  is  diagonal  and 
no  twinning  is  noticeable.  The  long  prisms  »>r  needles  are  twinned  in 
nearly  all  instances,  the  composition  plane  being  parallel  to  the  length  of 
the  prism.  The  direction  of  vibration  of  the  fastest  ray  is  nearly  parallel 
to  the  direction  of  the  length  of  the  prisms,  proving  them  to  be  elongated 
parallel  to  the  clinoaxis.  The  twinning  is  after  the  Manebach  law;  and 
the  cross  sections  show  that  the  crystals  have  a  clinodome  with  basal  plane 
and  possibly  with  clinopinacoids. 

These  crystals  branch  ont  in  two  different  ways.  In  some  cases  they 
appear  to  split,  the  parts  being  slightly  inclined  to  one  another  at  first,  and 
becoming  more  divergent  farther  on.  This  is  shown  in  the  right-hand  half 
of  PI.  LIII,  fig.  2.  Both  parts  are  twinned  in  the  same  manner  and  have 
the  same  optical  orientation — that  is,  each  is  a  prism  parallel  to  the  clino- 
axis. By  this  method  a  succession  of  branchings  takes  place,  the  prisms 
becoming  more  and  more  numerous  and  thinner,  often  terminating  in  a 
spherical  surface,  the  aggregation  in  thin  section  resembling  a  rounded 
bush  of  branching  stems,  especially  when  the  prisms  terminate  in  broad 
leaf-like  fronds,  which  often  happens  (PI.  LIV,  fig.  3).  In  other  cases  the 
branching  of  the  long,  twinned  prisms  is  seen  to  obey  a  cr}'stallographic 
law.  Short  prisms  project  from  opposite  sides  of  the  Manebach  twin  at  an 
angle  corresponding  to  that  between  the  vertical  axis  and  clinoaxis,  about 
64°  (left-hand  half  of  PI.  LIII,  fig.  2).  These  branches  are  prisms  parallel 
to  the  vertical  cr3'stallographic  axis.  They  are  sometimes  loug  and  slender, 
and  are  curved  to  a  position  parallel  to  that  of  the  prism  or  stem  from  which 
they  branch;  in  such  cases  the  bundle  of  feldspar  needles  will  consist  of 
numerous  prisms  elongated  parallel  to  the  vertical  axis,  and  a  central  one 
elongated  parallel  to  the  clinoaxis.  The  optical  orientation  of  prisms 
parallel  to  the  vertical  axis  will  differ  according  as  the  plane  of  the  optic 
axes  lies  in  the  plane  of  symmetry  or  is  at  right  angles  to  it.  In  the  first 
case  the  direction  of  vibration  of  the  slowest  ray  will  always  make  a  small 
angle  with  the  axis  of  the  prism,  or  be  parallel  to  it.  In  the  second  case 
the  speed  of  transmission  of  the  ray  vibrating  in  the  direction  of  the  prism 
axis  will  sometimes  be  less  and  at  other  times  greater  than  that  of  the  ray 
vibrating  at  right  angles  to  it,  according  to  which  side  it  is  ^dewed  from. 
Closely  allied  to  these  gi-owths  and  associated  with  them  are  delicate  rays 


416     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

or  needles  of  feldspar  which  are  composed  of  minute  stout  prisms  attached 
to  one  another  end  to  end,  in  parallel  position,  producing  a  rude  microscopic 
rod  with  uneven  sides.  These  jirisms  are  elongated  jmrallel  to  the  vertical 
axis,  and  for  the  reason  just  given  are  optically  sometimes  negative  and 
sometimes  positive,  or  they  may  all  be  positive.  They  form  branching 
arborescent  growths,  and  constitute  rays  of  spherulites,  usually  of  consid- 
erable size.  A  phase  of  this  kind  of  spherulitic  growth  is  shown  in  PI. 
LVI,  fig.  3.  Between  the  feldspar  rays  there  are  minute  grains  of  tridy- 
mite,  which  are  often  clustered  in  small  spherical  pellets  with  cavities 
between  them.  Such  spherulites  are  porous.  In  the  more  coarsely  crys- 
talline spherulites,  with  large  cavities,  the  same  kind  of  feldspar  crystals 
may  be  seen  with  a  low  magnifying  power.  Both  kinds  of  feldspar  prisms 
often  occur  in  the  same  spherulite. 

Some  spherulites  are  composed  of  a  dense,  micrographic  spherulite 
at  the  center,  which  passes  outward  into  the  branching  variety,  Avhicli  may 
be  porous  to  a  greater  or  less  degree,  the  free  silica  being  in  the  form  of 
tridymite.  In  some  areas  of  the  tridymite  grains  between  comparatively 
coarse  prisms  of  feldspar  (PL  LVI,  fig.  2)  there  are  crude  spherulitic  aggre- 
gations of  tridymite,  probably  composed  of  interpenetrating  tablets. 

LITHOPHYS^E. 

The  microstructure  of  the  lithophysse  can  not  be  studied  so  easily  as 
that  of  the  more  compact  spherulites,  because  of  the  slight  coherence  of 
the  crystals  composing  them  and  the  difficulty  of  preparing  thin  sections. 
But  in  many  cases  the  component  crystals  are  large  enough  to  be  seen  with 
a  pocket  lens,  and  their  character  and  arrangement  can  be  made  out.  It  is 
evident  in  the  case  of  hollow  or  gaping  porous  spherulites,  which  are  one 
phase  of  lithophysse,  that  the  mass  consists  of  short  prisms  of  orthoclase  or 
sanidine  attached  to  one  another  end  to  end,  in  a  manner  already  described 
for  some  spherulites.  These  jointed  rods  of  feldspar  radiate  from  what  was 
the  center  of  the  spherulite,  the  gaping  appearing  to  have  taken  place  after 
their  crystallization.  With  them  are  associated  tridymite,  quartz,  and 
fayalite.  When  there  is  no  marked  banding  in  the  surrounding  rock  mass, 
the  hollow  spherulite  may  have  the  form  represented  in  cross  section  in 
PI.  LVII,  fig.  1.     When  pronounced  banding  is  present  in  the  groundmass. 


LITIIOPIIYS.E.  417 

it  often  truversos  tlie  hollow  splierulite  aiul  the  fj-apiiiy  or  spaces  are  between 
the  layers,  as  in  fig-.  2. 

In  lithophysjy  proper  there  are  eoneentric  shells  of  (-rA-stals  and  con- 
centric spaces  between  them,  as  in  fig.  3  of  the  same  plate.     The  mimxte 
feldspar  prisms  in  the  shell  stand  radially  with  respect  to  the  center  of  the 
litho{)hys3e;  the  other  minerals  have  no  definite  arrangement.     Often  the 
tridymite  occurs  in  minute  pellets,  dotting  the  shells.     The  concentric  shells 
correspond   to  the   concentric  l)ands  of  coloi-  and  of  varying  composition 
which  characterize  certain  solid  spherulites.     They  probably  result  from  a 
pulsation  in  the  act  of  crystallization,  such  as   has  been  observed  in  the 
growth  of  crystals  and  spherulites  of  artificial  salts  when  the  latter  grow 
very  rapidly.     It  is  due  to  the  lowering  of  the  saturation  of  the  surrounding 
mother  liquor,  caused  by  the  sudden  liberation  of  heat  in  the  act  of  crystalli- 
zation, and  to  the  rapid  extraction  of  crystallizing  molecules.     The  spasmodic 
advance  of  the  crystallization  appears  to  have  produced  layers  that  were 
more  coherent  than  others,  and  the  latter  became  the  open  spaces  upon  the 
shrinkage  of  the  partly  crystallized  magma  before  its  final  crystallization. 
The  position  of  the  quartz,  tridymite,  and  fayalite  upon  the  surface  of  these 
shells  in  some  cases  indicates  that  they  formed  after  the  spaces  did.    When 
the  groundmass  is  markedly  banded  the  lithophysfe  are  often  modified,  as 
in  fig.  4  of  PI.  LVII.     Similar  structures  occur  in  hemispherical  lithophysfe, 
as  shown  in  figs.  5  and  6.     The  presence  of  these  cross  walls  proves  that 
the  shells  are  not  the  result  of  expanding  gas  bubbles,  but  must  have  been 
formed  by  the  contraction  of  the  magma  within  the  boundary  of  the  litho- 
physa  at  the  time  of  its  formation.     In  a  very  few  cases  there  appear  to  be 
evidences  of  a  slight  expansion,  which  is  shown  in  the  arching  of  the  layers 
of  the  groundmass  over  the  lithophysa,  as  in  fig.  7.     But  it  is  quite  possible 
that  the  cur\'ing  of  the  layers  may  have  antedated  the  formation  of  the 
lithophysa,  and  have  led  to  its  formation.     When  we   consider  that  the 
known  condensation  of  mass  in  the  passage  of  anhydi'ous  glasses  of  ortho- 
clase  and  quartz  into  the  crystal  form  is  about  10  per  cent  in  the  first  case 
and  16  per  cent  in  the  second,  and  when  we  remember  that  hydrous  glasses 
possess  still  greater  volume  than  the  anhydrous  ones,  we  are  prepared  to 
understand  the  comparatively  large   cavities  which  often  occur  in  these 
forms  of  rapid  crystallization.     In  the  case  of  the  dense  spherulites,  we 
must  assume  that  the  condensation  was  more  gradual,  though  rapid,  and 

MON  XXXn,  PT  II 27 


418     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

was  uniformly  toward  a  center,  the  surrounding  magma  closing  in  about  the 
growing  crystals,  which  must  always  happen  in  the  case  of  phenocrysts, 
though  generally  by  inappreciable  stages,  owing  to  the  comparative  slowness 
of  their  growth. 

The  r)rigiu  of  lithophysa'  must  be  due  to  the  more  abundant  presence 
of  water  vapor  in  spots  in  the  magma,  the  greater  viscosity  of  the  sur- 
rounding magma  and  its  generally  viscous  condition,  the  very  rapid 
crystallization  of  jointed  rods  of  feldspar  and  attendant  condensation,  fol- 
lowed by  the  further  condensation  of  the  remainder  of  the  mass  upon  the 
crystallization  of  the  silica,  which  must  have  taken  place  in  the  presence 
of  highly  heated  water  vapor.  The  minerals  produced  are  like  those 
crystallized  artificially  in  closed  tubes  in  the  presence  of  highly  heated 
water  vapor.^ 

In  certain  cases  the  spherulitic  growths  appear  to  be  little  more 
than  incipient  crystallizations,  although  the  spherulites  may  be  megascopic. 
They  are  only  faintly  doubly  refracting,  and  probably  consist  of  extremely 
minute  fibers.  Where  such  spherulites  occur  in  colored  banded  glass  the 
irregularly  twisted  bands  pass  through  the  brownish-  gray  spherulites  with- 
out interruption,  but  their  bright  colors  are  changed  to  brown,  with  the 
formation  of  opaque  grains  (PI.  L,  fig.  4).  Within  such  spherulites  in 
some  cases  there  are  delicate  branching  trichitic  needles,  radiating  from  the 
center,  which  are  probably  augitic,  besides  other  delicate  curved  needles 
with  high  index  of  refraction  and  strong  double  refraction,  whose  character 
was  not  made  out. 

In  some  forms  of  rhyolite  the  appeai'ance  of  welded  glass  fragments 
or  veil  structiire  is  retained,  although  the  mass  is  faintly  doubly  refracting 
and  mav  be  spherulitic  in  part,  incipient  spherulitic  needles  traversing  the 
rock  in  various  directions  without  regard  to  the  former  lines  of  flow,  which 
are  marked  by  opaque  dustlike  pai-ticles.  In  these  cases  it  is  evident  that 
the  spherulitic  crystallization  took  place  after  the  molten  mass  had  come 
to  rest. 

'  Friedel  and  Sarasin,  Bull.  Soc.  miiK^ialogie,  1879,  vol.  2,  p.  1158;  ibid.,  1880,  vol.  3,  p.  171; 
Comptes  rendns  Acad,  sci.,  Paris,  1881,  vol.  92,  p.  1374;  ibid.,  1883,  vol.  97,  pp.  290-294.  K.  von 
ChrustBchoff,  Am.  Chemist,  1883;  Tschermaku  mineral.  Mittheil.,  vol.  4,  p.  536.  Stanislas  Meunier, 
Comptes  rendus  Acad,  sci.,  Paris,  vol.  93,  1881,  p.  737.  De  Haldat,  Anuales  chimie,  vol.  46,  p.  70; 
Neues  .Tahrbuch  fiir  Mineral.,  1833,  p.  680.  A.  Daubree,  fitudes  syuthetiques,  etc.,  Paris,  1879,  pp. 
154-179.  For  a  historical  review  of  the  theories  regarding  the  fbriiiatiou  of  lithophysir,  scr  page  287 
of  the  author's  paper  on  Obsidian  Cliif,  in  the  Seventh  Annual  Report  of  the  U.  S.  Geological  Survey. 


AXIOLITIC  EHYOLITE.  419 

Tn  rcrtain  kinds  of  rlivolito,  apparoiitly  composed  of  welded  glass 
fraji'ineiits,  tliere  is  a  iiiicrosplu'rulitic  gmwth  wliicli  l)ears  a  definite  relation 
to  the  form  of  the  supposed  glass  fragments.  The  feldspar  fibers  are  in 
groups,  which  are  approximatel}'  normal  to  the  outline  of  the  fragments, 
and  radiate  inward.  Where  the  fragment  had  a  rudely  triangular  shajje 
the  central  part  often  attained  a  greater  degree  of  crystallization  than  the 
margin,  ;uid  sometimes  consists  of  distinct  crystals  of  feldspar  with  tridymite 
or  (juartz  and  a  small  amount  of  ferromagnesian  mineral.  Where  the 
fragments  were  long  and  narrow  the  si)herulitic  growth  from  the  sides 
inward  produced  the  effect  of  parallel  fi'inges — "axiolites"  of  Zii-kel.  This 
tendenc'S'  to  develop  spherulitic  growths  from  old  suifaces  or  cracks  is 
shown  in  another  modification  of  the  rock  in  which  the  axiolitic  structure 
can  be  seen  megascopically.  In  hand  specimens  these  varieties  appear  to 
be  dark  lithoidal  or  glassy  rocks,  traversed  in  all  directions  by  narrow 
spherulitic  bands.  In  the  glassy  forms  of  the  rock  the  black  glass  inclosed 
by  the  lithoidal  bands  occasional!}-  falls  out,  like  a  kernel  from  a  shell, 
proving  the  spherulitic  portion  to  be  a  growth  along  intersecting  planes. 

In  thin  section  it  is  observed  that  the  spherulitic  bands  have  a  dark 
line  along  their  centers,  as  though  the}'  were  ancient  cracks.  They  inter- 
sect one  another  in  some  cases,  but  are  not  persistent  in  others.  Their 
behavior  toward  phenocrysts  when  present  is  the  same  as  that  of  perlitic 
cracks.  They  encircle  them,  but  never  traverse  them  (PI.  LV,  fig.  4). 
They  do  not  often  occur  in  as  many  concentric  circles  as  ordinary  perlitic 
cracking,  but  they  are  unquestionably  of  the  same  general  character, 
namely,  the  cracking-  of  an  amorphous  glassy  substance.  The  spherulitic 
crystallization  is  subsequent  to  the  cracking  and  is  located  along  the  cracks. 
It  is  like  other  forms  of  spherulitic  growths  in  these  glasses,  and  is  evidenth' 
only  a  special  case.  In  one  instance  similar  spherulitic  growth  had  formetl 
about  the  edge  of  an  open  crack  in  such  a  manner  as  to  show  that  the 
magma  had  been  so  viscous  jjrevious  to  its  last  movement  that  a  small  gap 
in  it  was  not  closed.  Upon  its  walk  pellets  of  tridymite  formed.  It  nmst 
have  been  after  it  had  reached  this  highl}-  viscous  state  that  this  jjarticular 
spherulitic  crystallization  took  ])lace.  In  cases  where  perlitic  glasses 
contain  spherulites  it  is  observed  that  the  perlitic  cracks  encircle  spheralites 
in  the  same  manner  as  they  encircle  phenocrysts,  and  do  not  traverse  them. 
The  perlitic  cracking  is  subsequent  to  the  spherulitic  crystallization  and  is 


420  GEOLOGY  OF  THE  YELLOWSTONE  I^ATIONAL  PAEK. 

confined  to  the  glassy  grouudmass.  In  the .  rather  uncommon  occurrences 
just  noted,  where  a  crackmg  has  been  followed  by  crystallization,  it  is 
probable  that  the  shrinkage  and  cracking  took  place  in  a  highly  heated, 
stiff  mass,  which  was  sxibsequently  welded  together,  as  the  collapsed  pumice 
may  have  been — that  is,  it  may  have  been  surrounded  by  a  hotter  portion  of 
the  same  lava  flow  and  its  temperature  may  have  been  raised  to  some  extent. 
Instances  of  this  kind  of  structure  are  found  on  the  continental  divide 
south  of  Madison  Lake  and  on  the  summit  of  the  west  wall  of  Bechler 
Canyon,  5  miles  from  its  mouth  (1945,  1946),  and  also  in  the  vicinity  of 
the  Lower  Geyser  Basin. 

From  the  foregoing  it  appears   that  certain  forms  of  crystallization 
which  unquestionably  take  place  in  molten  magmas  at  or  near  their  point 
of  solidification,  and  which  niaj'  be  classed  as  pyrogenous  and  primary, 
may  take  place  in  a  mass  at  a  time  subsequent  to  the  development  of  fea- 
tures which  seem  to  be  dependent  upon  a  certain  amount  of  rigidity  of 
the  magma,  such  as  the  formation  of  cracks.     Such  rigidity  is  generally 
supposed    to    indicate    perfect    solidification    and    completed    pyrogenous 
crystallization;  and  undoubtedly  it  does  in  most  cases.    But  rigidity  has 
a  relative  significance,   and  what  is  rigid  with  respect  to  a  force  acting 
through  an  extremely  short  period  of  time  may  be  plastic  toward  the  same 
force  acting  through  longer  time.     Hence  a  highly  viscous  magma  may 
be  torn  to  fragments  by  an  explosion,  or  be  highly  inflated  by  the  sudden 
expansion  of  vapor,  and  in  some  cases  be  still  viscous.    Generally,  however, 
the  sudden  expansion  and  escape  of  inclosed  vapors  tend  to  lower  the  tem- 
perature of  the  magma  and  increase  its  viscosity.     But  it  may  not  necessa- 
rily be  solid  or  rigid.     Similarly,  shrinkage  cracks  may  be  produced  in  a 
'/iscous  mass  by  sudden  contraction  before  the  mass  has  solidified  and  while 
it  is  still  highly  heated,  the  fracturing  being  due  to  the  rapidity  of  change 
of  volume,  and  not  necessarily  to  the  absolute  amount  of  contraction.     Such 
sudden  contraction  of  imsolidified  lavas  is  not  of  common  occurrence,  it 
would  seem,  but  the  instances  of  postperlitic  spherulitic  crystallization  just 
described  indicate  its  occasional  occurrence. 

In  the  massive  glasses  which  are  striped  and  marked  with  bands  of 
various  color  it  is  sometimes  noticed  that  lines  of  color  traverse  the  mass 
like  ancient  fractures  which  closed  up  before  the  solidification  of  the  mass. 
They  pass  across  the  lines  of  flow,  which  sometimes  end  abruptly  against 


INTEKSFHEKULITIC  CRYSTALLIZATION.  421 

these  lines,  appearing  as  tliougli  faulted  and  displaced  to  a  slight  extent. 
In  many  instances  the  arrangement  of  the  streaks  of  color  is  such  as  to 
indicate  that  the  compact  mass  was  once  an  aggregate  of  fragments  of 
similar  magma,  the  lines  of  flow  having  various  orientations  in  the  different 
fragments.  They  have  been  welded  into  one  contiiuious  homogeneous 
mass.  In  those  varieties  of  rhyolite  in  which  the  first  kind  of  spherulites 
are  developed — namely,  the  compact  ones  which  are  closely  related  to 
micrographic  intergrowths — there  are  irregularly  shaped  areas  bet^^'eeu 
bands  and  clusters  of  mici'oscopie  spherulites  which  exhibit  a  different  sort 
of  crystallization.  They  are  more  highly  crystalline — that  is,  the  size  of 
the  individual  crystals  is  larger.  The  spherixlites  bordering  these  areas 
generally  terminate  in  distinct  prisms  oi  orthoclase,  which  have  already 
been  described,  while  isolated  crystals  of  orthoclase  of  similar  habit  and 
size  lie  in  various  positions  within  the  more  crystalline  area.  The  cement 
to  these  crystals  in  some  instaiaces  is  trid}'mite,  in  minute  grains  or  in  well- 
developed  twinned  crystals  with  characteristic  wedge-shaped  cross  section. 
In  other  cases  the  quartz  forms  the  cement,  and  is  wholly  allotriomorphic, 
producing  a  micropoikilitic  structure  (PI.  LIV,  fig.  4).  In  places  some  of 
the  feldspar  prisms  are  nearly  parallel  to  one  another,  so  that  the  interstitial 
quartz  appears  in  the  shape  of  thin  strips  or  needles,  which  is  misleading, 
producing  the  effect  of  idiomorphic  crystals.  This  quartz  is  unquestion- 
ably of  igneous  or  of  aqueo-igneous  origin,  occupying  the  same  relation 
to  the  orthoclase  as  does  the  tridymite  in  the  other  cases,  the  development 
of  one  or  the  other  depending  on  very  slight  differences  of  23hysical  condi- 
tion, as  demonstrated  by  experiment.  In  some  experiments  both  forms 
have  been  produced  together.  Often  the  tridymite  is  accompanied  by  gas 
cavities  of  variable  dimensions.  With  the  orthoclase  and  quartz  oi-  tridy- 
mite are  some  magnetite  and  small  amounts  of  ferromagnesian  minerals. 
The  latter  differ  in  character  in  different  occuiTcnces,  and  may  be  faj^alite, 
mica,  or  tourmaline,  and  in  rare  instances  possibly  garnet.  The  fayalite 
forms  comparatively  large  individuals,  allotriomorphic  with  respect  to  the 
feldspar,  sometimes  with  an  opaque  border,  which  raaj-  entirel}'  replace  the 
original  individual. 

Tourmaline  and  mica  are  found  in  minute  crystals  about  0.025  mm. 
long  and  0.01  mm.  thick.  They  are  abundant  in  places,  or  lie  scattered 
through  the  tridymite  and  quartz,  and  also  in  the  margin  of  the  bordering 


422     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

splienilites.  Sometimes  they  occm-  together,  but  usually  independently. 
The  tourmaline  is  recognized  by  its  strong  absorption  and  by  its  other 
optical  properties.  Its  color  is  brownish  green  to  colorless.  The  mica 
is  green,  and  also  yellowish  brown  to  reddish.  The  green  mica  is  easily 
confounded  with  the  toiu-maline,  but  may  be  distinguished  by  the  direction 
of  the  absorption.  The  tourmaline  and  mica  are  idiomor})hic,  and  must 
have  crystallized  just  before  the  outer  jiortion  of  the  small  spherulites  did, 
and  also  before  the  tridymite  and  quartz  in  which  they  lie.  They  are  con- 
fined to  the  region  of  these  interspherulitic  spaces  and  are  not  found 
scattered  indiscriminately  through  the  spherulites.  A  mineral  which  is 
probably  garnet  occurs  in '  the  same  manner  as  tounnaline  and  mica,  and 
forms  irregular  graiias,  which  are  colorless  and  isotropic  and  have  a  high 
index  of  refraction.  Occasionally  the  more  coarsely  crystallized  quartz  and 
feldspar  in  the  interspherulitic  spaces  are  traversed  by  opaque  material 
segregated  in  curved  layers,  suggesting  the  structure  of  Eozoon.  In  PI. 
LV,  fig.  2,  these  streaks  appear  to  be  continuations  of  the  lines  of  trichites 
that  traverse  the  spherulites  and  originally  marked  the  flow  planes  in  the 
lava.  They  have  been  displaced  by  the  crystallization  of  the  larger  crj^stals 
of  feldsijar  and  quartz. 

In  the  banded  lithoidal  rhyolite  the  layers,  often  microscopic  in  size, 
consist  of  minute  spherulites  alternating  with  various  modifications  of  the 
crystallizations  just  described.  These  are  really  holocrystalline,  with  gas 
cavities,  a  phase  of  miarolitic  structure.  The  size  of  the  cavities  is  some- 
times consideralile,  and  may  be  observed  megascopically,  giving  rise  to 
planes  of  weakness  in  the  rock  along  which  it  splits.  The  microspherulitic 
layers  may  also  grade  into  glassy  layers,  so  that  holocrystalline  and  glassy 
layers  alternate  with  one  another  in  some  modifications  of  rhyolite,  notably 
in  certahi  parts  of  Ob.sidian  Cliff.  This  is  illustrated  in  PI.  LVI,  fig.  4, 
representing  a  section  across  laminated  lithoidite.  Microspherulitic  layers 
alternate  with  layers  containing  comparatively  large  feldspar  crystals  with 
quartz  and  tridymite.  In  one  layer  the  coloring  matter  is  segregated  in 
streaks,  like  ribs. 

MICROGRASrUIiAR  STRUCTURE. 

While  the  glassy  and  spherulitic  structures  are  those  most  commonly 
found  in  the  rhyolites  of  the  Yellowstone  Park,  several  modifications  of 


U.  S.  QEOLOGICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.   LVI 


(A)  X    13 


(B)  I  20 


(C)  I    12 


( D)   X    12 


PHOTOMICROGRAPHS    OF  SPHERULITIC    STRUCTURES    AND    FELDSPAR    MICROLITES 


THE  MELIOTYPE  PRINTING  CO..  BOSTON 


U.  8.  OEOLOQICAL  SURVEY 


MONOORAPH  XXXII      PART  II      PL.    LVtl 


^' 


ris^rvv?iJ,<v^>5^?^^K?^yT"'\^^ 


Ni,SX^\\\.);s\ss\\\\X\\\\\\\\\\X-^<S--X\XN 


JSiSiiSiiJ^iiiSy 


•^■■^■t  "^  -'*^T'!l?!2" 


/S'iSSSSS^ 


^^^AT  ^  ^ 


DIAGRAMS  OF   LITHOPHYS/E 


MICROSTKUUTURES  IN  IMIYOLITES.  423 

the  rock  exhibit  a  more  or  less  evenly  granular  niicrostructure,  which  may 
be  microcrystalline  or  microcryptocrystalline.  In  places  it  is  hyjndiomor- 
pliic  ;  in  others  the  <>Tains  nre  so  minute  as  not  to  be  distinctly  discernible. 
In  some  cases  this  structure  accompanies  a  distinct  How  structure  which  is 
marked  by  opaque  grains.  In  others  no  flow  structure  is  noticealjle.  It 
appears  to  be  a  primary  crystallization  in  many  cases,  even  where  a  flow 
stnicture  is  observed,  when  it  must  have  been  a  crystallization  accompany- 
ing the  final  solidification  of  the  rock.  But  it  is  undoubtedly  secondaiy  in 
some  instances,  which  are  not  of  frequent  occurrence  among  the  extremely 
little  altered  rhyolites  of  the  Yellowstone  Park. 

RELATIONS  OF   THE  VARIOUS  MICROSTRUCTURES   TO  ONE    ANOTHER 

IN  THE  ROCK  MASS. 

The  various  microstructures  which  have  been  described  in  detail  in  a 
systematic  manner  occur  together  in  quite  diff'erent  combinations.  Pumice 
is  found  associated  with  dense  glass,  and  grading  into  it.  Usually  the 
surface  of  a  flow  is  pumiceous,  as  at  Obsidian  Clifi",  but  the  easily  abraded 
pumice  has  undoubtedly  been  carried  away  by  glaciation  in  most  places. 
It  is  not,  however,  a  necessary  accompaniment  of  obsidian  flows,  as  is  shown 
by  such  lava  streams  in  the  island  of  Lipari.  It  was  probably  more 
frequent  in  the  Yellowstone  region.  Pumiceous  and  compact  glass  is  often 
intermingled  over  the  surface  of  the  plateaus.  The  dense  glass  is  usually 
microlitic  and  often  spherulitic,  but  in  no  ease  has  pumice  been  found  to 
contain  spherulites.     They  occur  in  vesicular  obsidian. 

The  various  kinds  of  microlitic  glass  may  be  found  in  close  association 
with  one  another,  and  all  the  diff'erent  forms  of  incipient  crystallization  and 
spherulitic  aggregation  may  be  found  in  a  single  specimen  of  rock,  even  in 
one  thin  section.  It  oftener  happens  that  a  particular  form  of  spherulitic 
growth  prevails  throughout  a  considerable  mass  of  rock.  But  in  such 
occurrences  as  the  rhyolitic  flow  at  Obsidian  Cliff  there  are  parts  of  the 
mass  in  which  there  is  great  variability  in  the  microstructure  within  short 
distances.  In  a  great  many  localities  it  is  clearly  seen  that  the  thick  flows 
of  rhyolitic  lava  were  pumiceous  and  glassy  at  the  top  and  glassy  for 
some  distance  downward,  usually  with  megascopic  spherulites.  They  then 
became  lithoidal  by  the  development  of  microspherulitic  structure,  as  in  the 
lithoidite  at  Obsidian  Cliff".     The  microcrystalline  to  microcryptocrystalline 


424     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

modifications  exist  in  some  cases  near  the  bottom  of  the  lava  sheet,  but  no 
definite  mode  of  occurrence  has  been  made  out.  In  places  the  bottom  part 
of  the  flow  is  glassy  and  dense ;  in  places  it  rests  on  a  bed  of  pumiceous 
tuff  and  is  lithoidal;  that  overlying  the  rhyolitic  tuff  on  Mount  Everts  is 
microcrystalline  (1762).  The  indurated  tuff,  indistinguishable  from  the 
overlying  massive  lava,  exhibits  a  fragmentary  glass  structure,  with  some 
axiolites,  and  occasional  spherulitic  structure  independent  of  the  outline  of 
the  fragments,  while  parts  of  the  mass  are  isotropic. 

LAlMIlSrATION  AND  BANDING. 

Lamination  and  banding  are  highly  developed  in  the  lithoidal  portion 
of  the  rhyolitic  flow  at  Obsidian  Cliff.  They  are  very  generally  present 
in  a  higher  or  lower  degree  in  all  the  rhyolites  of  the  Park.  In  fact  they 
form  one  of  the  commonest  characteristics  of  acid  lavas,  and  are  equally 
uncommon  among  the  basic  ones.  They  are  clearly  due  to  the  spreading 
out  through  flowage  of  a  more  or  less  heterogeneous  caseous  fluid.  Homo- 
geneous portions  of  the  mass,  of  whatever  shape,  will  spread  out  and  flatten 
during  the  flow  of  the  whole  body  of  lava,  becoming  thin  lenticular  layers 
if  the  spreading  or  flow  is  sufficiently  extended.  A  mass  consisting  of  por- 
tions which  differed  from  one  another  in  color  or  composition  would 
become,  after  spreading  out  upon  the  surface  of  the  earth,  a  body  made  up 
of  layers  of  different  color  or  composition,  which  Avould  wedge  out  in  thin 
edo-es  between  one  another.  A  cross  section  of  such  a  body  would  exhibit 
a  more  or  less  streaked,  banded,  or  laminated  structure  according  to  the 
original  size  of  the  different  portions  and  to  the  extent  of  the  spreading. 

In  the  case  of  the  lithoidite  at  Obsidian  Cliff,  it  can  be  shown  that 
the  cause  of  the  differences  in  the  layers  was  unquestionably  the  different 
amounts  of  water  vapor  present  in  them.  For  in  the  lithoidite  the 
layers  differ  in  their  degree  of  crystallization,  some  being  glassy,  others 
microspherulitic,  others  more  coarsely  so  and  porous,  while  others  are 
microgranular  with  larger  cavities.  Some  layers  have  locally  developed 
crystallization  in  the  form  of  large  spherulites  and  lithophysse.  In  the 
obsidian  the  differences  consist  in  layers  of  spherulites,  large  and  small,  in 
bands  of  lithophysse,  and  in  layers  abounding  in  micrographic  feldspars, 
microscopic  spherulites,  microlites,  and  trichites — that  is,  in  the  different 
phases  of  crystallization.     Near  the  surface  of  the  lava  flow  the  laminated 


LAMINATION  OF  RHYOLITES.  425 

condition  of  the  rock  sliows  itself  in  layers  of  compact  <)lass  full  of  micro- 
lites  wliicli  alternate  with  layers  full  of  gas  cavities  and  with  little  or  no 
microlites.  And  in  the  highly  pumiceous  part  of  the  flow  it  is  seen  that 
the  inflation  of  the  glass  is  more  marked  in  some  layei's,  while  there  are 
spots  in  which  the  inflaticm  is  specially  pronounced.  These  differences 
in  the  pumiceous  parts  of  the  rock  are  due  to  variable  amounts  of  water 
vapor  in  the  layers  of  the  lava;  and  similar  differences  must  have  existed 
in  lo'\\'er  parts  of  the  same  lava  sheet.  Moreover,  the  kinds  of  minerals 
crystallized  are  those  whose  formation  is  known  to  be  aided  by  the  pres- 
ence of  water  vapor  and  other  vapors.  Further,  the  localization  of  more 
abundant  water  vapor,  which  gave  rise  to  specially  inflated  spots  in  the 
pumice,  is  undoubtedly  the  cause  of  the  crystallization  of  isolated  spheru- 
lites  in  the  compact  glass. 

The  greater  frequency  of  lamination  and  localized  crystallization  in 
acid  lavas  as  compared  with  basic  ones  is  a  conseqvience  of  the  generally 
greater  viscosity  of  acid  lavas  at  the  time  of  their  eruption.  The  basic 
rocks  have  a  considerably  lower  melting  point  and  are  much  more  liquid 
up  to  very  near  the  temperature  of  solidification.  Hence  diffusion  would 
take  place  more  rapidly  and  the  magma  would  be  more  homogeneous, 
other  things  being  equal.  The  heterogeneity  of  the  acid  lavas,  so  far  as 
known,  is  confined  to  the  distribution  of  vapors,  presumably  of  water, 
and  suggests  that  the  water  thus  irregularl}-  disseminated  has  not  existed 
within  the  magma  long  enough  to  become  uniformly  diffused.  It  must 
therefore  be  looked  upon  as  water  absorbed  near  the  earth's  surface. 
Whether  there  may  also  have  existed  water  vapor  in  the  magma  having 
a  much  longer  connection  with  it,  is  more  difficult  to  demonstrate,  though 
it  is  highly  probable. 


426 


GEOLOGY  OF  THE  YELLOWSTOISTE  Is'ATIONAL  PARK. 


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CHEMICAL  COMPOSITION  OF  RHYOLITKS.  427 

VARIATIONS  IN   CO»IPOSITU)N   AMt)N(J   THE   RHYOLiITES. 

The  lavas  which  wouhl  be  classed  together  as  rhyolites  on  account  of 
their  field  relationships  and  similarity  of  habit  are  found  to  differ  somewhat 
in  composition,  both  chemical  and  mineralog:ical.  The  chemical  composi- 
tion of  the  commonest  and  alsci  of  the  extreme  varieties  is  shown  by  the 
analyses  in  the  accompanying-  table.  With  them  have  been  placed  for 
comparison  analyses  of  the  most  siliceous  intrusive  rocks  from  several  locali- 
ties in  the  Park. 

The  range  of  silica  in  the  rhyoHte  is  from  70.92  to  75.89  per  cent. 
Four  varieties  contain  between  74.70  and  75.89  per  cent.  They  are  the 
flow  forming  Obsidian  Cliff,  in  part  obsidian,  in  part  lithoidite;  lithoidal 
rock  at  Mount  Sheridan;  obsidian  from  the  Elephant  Back,  and  lithoidal 
rhyolite  from  Madison  Plateau  north  of  the  canyon.  These  represent 
the  normal  rhyolite  of  the  region.  Another  variety  of  rhyolite,  which 
appears  to  be  a  common  form  and  carries  abundant  quartz  phenocrysts, 
has  71.85  per  cent  of  silica.  It  is  lithoidal  and  is  part  of  the  great  mass 
forming  the  table-topped  spurs  at  the  head  of  Tower  Creek.  A  variety 
of  obsidian  occurring  north  of  Oljsidian  Cliff  and  apparently  a  portion  of 
the  obsidian  flow  of  that  locality,  though  not  certainly  so,  contains  72.59 
per  cent  of  silica.  This  rock  is  more  of  a  pitchstone  than  obsidian,  and 
has  a  dull  resinous  luster.  The  variety  lowest  in  silica,  with  70.92  per 
cent,  constitutes  the  lava  in  the  immediate  vicinity  of  the  Upper  Greyser 
Basin.  It  is  lithoidal  and  dark  colored,  without  noticeable  phenocrysts  of 
quartz. 

Alumina  varies  but  slightly  in  these  rhyohtes,  from  12.27  to  14.11  per 
cent.  The  alkaUes  are  moderately  high,  being  6.65  to  8.50  per  cent,  with 
soda  in  excess  of  the  potash  in  most  cases.  The  alkaline  earths  are  the  most 
variable,  lime  ranging  from  2.25  to  0.68  per  cent,  magnesia  from  1.05  to 
0.07  per  cent,  and  ferric  oxide  from  3.54  to  0.42  per  cent.  Ferrous  oxide 
forms  1.55  to  0.08  per  cent,  the  sum  of  the  iron  oxides  ranging  from  4.20  to 
1.63  per  cent.  There  is  about  0.30  per  cent  of  titanium  oxide  in  three  cases, 
and  none  was  found  in  tlu-ee  other  cases.  Phosphorous  pentoxide  was  found 
only  in  the  less  siliceous  varieties. 

The  chemical  composition  of  the  rhyolite  from  the  head  of  Tower 
Creek  is  not  wholly  in  accord  with  the  mineral  composition  and  habit  of 
the  rock,  which  has  abundant  glassy  feldspars  and  quartzes,  plagioclase  being 


428     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

prominent.  There  are  some  small  crystals  of  augite  and  magnetite.  The 
mineral  composition  is  not  very  different  from  that  of  many  other  rhyolites, 
but  there  are  minute  inclusions  of  dark-colored  rock  not  clearly  recogniz- 
able, probably  basalt.  Tliis  would  explain  the  rather  abnormal  amount  of 
lime  and  the  low  silica. 

The  chemical  composition  of  the  lava  from  the  Upper  Geyser  Basin 
is  in  accord  with  the  mineral  composition  and  habit  of  the  rock,  which 
rejjresents  the  least  siliceous  varieties  occurring  in  the  Yellowstone  Park. 
The  rock  is  dull  brownish  gray,  with  numerous  small  phenocrysts,  which 
are  mostly  white  feldspars.  These  are  plagioclase,  apparently  oligoclase- 
andesine,  the  presence  of  orthoclase  being  doubtful.  There  Is  no  quai'tz. 
Magnetite  is  in  comparatively  large  grains ;  augite  is  partly  altered,  and  has 
dropped  out  in  preparing  the  sections.  Apatite  and  zircon  occur.  The 
groundmass  is  microspherulitic,  with  brownish  spherulites  and  numerous 
strongly  doubly  refracting  needles,  dotted  with  minute  opaque  grains. 
These  are  altered  microlites  of  augite  with  attached  grains  of  magnetite. 
These  brownish  microspherulites  with  dark  needles  are  characteristic  of  this 
variety  of  rhyolite,  which  might  properly  be  classed  as  dacite.  Occurring, 
as  they  do,  as  rather  infrequent  modifications  of  the  great  bodies  of  rhyo- 
lite, the}'^  are  here  treated  as  dacitic  facies  of  rhyolite.  Exposures  of  this 
rock  occur  back  of  the  Grand  Geyser  and  in  a  small  hill  near  the  Splendid 
Geyser,  in  the  Upper  Geyser  Basin.  It  forms  the  bluff  west  of  the  Paint 
Pots,  near  the  road  in  Geyser  Meadow,  where  the  finely  vesicular  rocks 
resemble  a  basic  andesite  or  basalt  in  outward  appearance,  but  contain 
phenocrysts  of  quartz,  sanidine,  and  plagioclase.  There  are  other  localities, 
less  accessible,  in  which  dacitic  facies  of  the  rhyolite  occur. 

The  chemical  composition  of  pitchstone  north  of  Obsidian  Cliff  is  that 
of  a  dacitic  rather  than  of  a  rhyolitic  glass,  and  yet  the  microscopical 
characters  indicate  a  closer  relation  to  basalt,  or  augite-andesite.  There 
are,  in  fact,  small  inclusions  of  basalt  scattered  through  the  glass.  The 
character  of  the  microscopic  crystals  and  their  similarity  to  those  of  the 
inclosed  basalt  have  been  pointed  out.  The  comparatively  high  percentage 
of  lime  and  magnesia,  and  tlie  much  greater  amount  of  soda  than  of  potash, 
correspond  to  these  niineralogical  characteristics,  and  are  not  wholly  due 
to  the  inclusions  of  basalt.     The  different  specimens  of  this  dull  obsidian 


GUEMICAL  COMPOSITION  OF  KHYOLITES.  429 

or  pitchstone  exliibit  a  gradual  transition  in  tlio  character  and  proportions 
of  tho  niicroscojiic  crystals  or  niicrolites  from  those  of  normal  obsidian  to 
the  abnormal  basaltic  facies  (21(14).  It  is  to  be  noted  that  this  facies  is  not 
dacitic  in  its  habit,  although  the  silica  percentage  is  72.59.  Such  facies 
art'  luiconimon.  The  occurrence,  as  well  as  its  transition  into  obsidian 
with  lithojihysaj,  suggests  that  its  magma  is  a  transition  form  between 
rhyolite  and  basalt. 

The  slight  variations  in  composition  which  are  expressed  by  the  min- 
eralogical  character  of  the  rhyolite  in  different  places  do  not  appear  to  be 
connected  Avith  any  particular  locality,  although  they  are  sometimes  char- 
acteristic of  large  areas  of  rhyolite.  They  recur  in  all  parts  of  the  region, 
and  appear  to  be  oft-repeated  moditications  of  the  magma,  dependent  as 
much  on  physical  conditions  as  on  chemical  variability. 

From  the  table  of  chemical  aiiah^ses  (p.  426)  it  is  seen  that  the  most 
siliceous  facies  of  the  Holmes  bysmalith,  which  occurs  along  its  margin  at 
Echo  Peak,  is  almost  identical  chemically  with  portions  of  the  lava  flow  at 
Obsidian  Cliff,  while  the  main  mass  of  the  bysmalith  has  nearly  the  compo- 
sition of  the  dacitic  facies  of  the  rhyolite  at  the  Upper  Geyser  Basin,  but  is 
lower  in  potash  and  higher  iu  alumina.  The  fine-grained  granite  from  the 
volcanic  core  of  the  Crandall  volcano  has  almost  exactly  the  same  composi- 
tion as  the  rhyolite  from  the  Upper  Geyser  Basin.  The  dacite-porphyries 
of  Bunsen  Peak  and  Birch  Hills  have  nearly  the  composition  of  the  rhyolite 
from  Tower  Creek  and  of  the  abnormal  obsidian  from  the  plateau  east  of 
Willow  Park,  but  they'  are  higher  in  alumina  and  a  trifle  higher  in  lime, 
with  a  little  less  silica.  The  quartz-mica-diorite-porphyry  from  the  volcanic 
core  of  Electric  Peak,  though  nearly  as  high  in  silica  as  the  rhyolite  of  the 
Upper  Geyser  Basin,  is  distinctly  higher  in  lime  and  lower  iu  potash.  On 
the  other  hand,  the  trachytic  rhyolite  from  the  flanks  of  Sunset  Peak,  north 
of  the  Park  boundary,  while  agreeing  with  the  rhyolite  of  the  Upper 
Geyser  Basin  iu  most  of  its  chemical  coriiposition,  is  lower  in  soda  and 
higher  in  potash. 

The  rocks  here  compared  with  the  rhyolite  are  the  more  acid  phases 
of  magmas  that  belong  to  much  earlier  periods  of  eruption.  They  show 
the  tendency  of  these  magmas  to  differentiate  into  facies  whose  composition 
approaches  that  of  the  i-hyolite  more  or  less  closely. 


430  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

INTERMIXGLED   RHYOLITE  AlVD  BASAI.T. 

Ill  several  localities,  chiefly  on  the  plateau  west  of  Beaver  Lake  and 
on  the  south  bank  of  Gardiner  River  south  of  Bunsen  Peak,  there  are  lavas 
whose  abnormal  appearance  is  striking.  At  the  first-mentioned  locality  the 
rock  is  partly  litlioidal  and  dark  gray,  with  phenocrysts  of  feldspar  and 
quartz,  partly  purplish  gray  to  reddish,  and  finally  porous  or  vesicular. 
The  latter  contains  small  phenocrysts  of  feldspar,  generally  lath-shaped  or 
tabular,  besides  quartz  grains,  and  occasionally  olivine.  The  vesicular 
cavities  have  minute  white  pellets  of  tridymite.  Other  parts  of  the  same 
rock  are  dark  gray  and  litlioidal  or  glassy,  with  dull  gray  spherulites,  8  or 
10  mm.  in  diameter  and  smaller.  These  are  distinctly  radially  fibrous  and 
slightly  porous,  in  some  parts  of  the  rock  passing  into  hollow  spherulites 
(1804,  1806).  These  various  modifications  of  the  rock  grade  into  one 
another  and  intermingle  in  streaks  without  any  distinct  line  of  demarca- 
tion between  them.  The  appearance  is  that  of  a  completely  fused  mass  of 
somewhat  ditferently  constituted  materials.  In  places  in  this  vicinity  the 
spherulitic  glassy  rhyolite  incloses  distinct  fragments  of  basalt  (1802). 

The  microscopical  characteristics  are  somewhat  different  from  those  of 
normal  rhyolite.  The  glassy  portion  in  thin  section  is  in  places  colorless 
and  sometimes  perlitic.  The  number  of  microlites  varies;  in  some  places 
they  are  scarce,  in  others  abundant.  They  consist  of  rectangular  feldspars, 
and  some  with  pointed  corners.  There  are  microlites  of  quartz  and  micro- 
prisms  of  augite,  with  a  few  of  hornblende,  and  in  some  instances  minute 
hexagonal  plates  of  hematite  or  biotite.  In  places  the  colorless  glass  grades 
into  brown  along  the  contact  with  basalt.  The  brown  glass  contains  crvstals 
from  the  basalt,  and  appears  to  have  been  produced  by  a  fusion  of  the 
latter,  larger  crystals  of  feldspar  occasionally  projecting'  into  the  brown 
glass.  The  colorless  glass  has  penetrated  vesicular  cavities  in  the  basalt 
and  has  partly  fused  the  latter.  The  brown  glass  grades  into  globulitic 
and  trichitic  colorless  glass  by  "the  concentration  of  the  coloring  material. 
By  a  more  distinct  ciystallization  there  arise  augite  prisms  and  needles 
with  minute  grains  of  magnetite  attached  to  their  surface;  also  thin  curved 
needles  or  "hairs"  of  augite,  to  which  are  attached  clusters  and  clouds  of 
minute  specks  of  magnetite.  The  extremely  delicate  hair-like  needles 
of  augite  are  straight  or  curved  and  sometimes  curled  up  at  the  end. 
Occasionally  the  stouter  needles  are  broken  into  lines  of  "margarites"  whose 


INTKRMINGLEI)  KHYOLITE  AND  BASALT.  431 

augitic  chanvcter  is  iiiuiuestioiuil^le.  Tliese  iuigite  needles  often  project 
from  the  basalt  into  the  glass.  In  cue  case  the  colorless  glass  contact  zone 
contains  moss-like  aggregates  of  red  and  opaque  iron  oxide  attached  to 
augite  needles. 

Spherulitic  crystallization  has  taken  on  a  variety  of  forms.  In  several 
instances  it  produces  a  border  against  the  basalt,  radiating  into  the  glass, 
in  which  there  are  also  isolated  spherulites  of  the  same  character — that  is, 
ilistinctly  fibrous  and  faintly  doubly  refracting,  with  no  well-marked  dark 
arms.  Where  megascopic  spherulites  occur  they  are  distinctly  fibrous  and 
porous,  with  spherules  of  tridymite.  The  libers  or  microprisms  are  mostly 
optically  positive;  occasionally  negative.  These  spherulites  surround  pheno- 
crysts  and  also  fragments  of  basalt.  Some  smaller  spherulites  are  brown 
in  transmitted  light  and  have  brown  curved  rays  or  fibers,  distinct  from 
those  of  feldspar.  In  the  rhyolite-basalt  fusion  on  Gardiner  River  the  augite 
needles  associated  with  the  spherulites  have  been  beautifully  developed, 
and  will  be  described  in  that  connection. 

The  phenoci-ysts  of  quartz  are  sometimes  rounded;  those  of  sanidine 
in  certain  cases  possess  a  marginal  zone  which  is  clouded,  and  appears 
to  contain  another  transparent  mineral.  This  exhibits  uniform  orienta- 
tion throughout.  Porphyritical  plagioclase  is  less  conmion.  Fragments  of 
basalt  and  detached  crystals  from  it  are  scattered  through  the  rhyolitic  rock. 
In  one  instance  the  rock  mass  had  more  of  the  appearance  of  basalt  than  of 
rhyolite,  and  yet  contained  rounded  phenocrysts  of  quartz  with  numerous 
olivines,  occasionally  in  skeleton  forms,  and  plagioclase  and  augite,  with 
one  individual  of  sanidine.  The  augites  in  the  basalt  are  pale  green  in 
thin  section;  those  from  the  rhyolite  are  stronger  green. 

With  the  pellets  of  tridymite  which  are  attached  to  the  sides  of  cavities 
in  the  basalt  are  occasional  projecting  crystals  of  brownish-green  horn- 
blende. Parts  of  the  rhyolite  are  holocrystalline,  with  an  almost  micro- 
cryptocrystalline  texture  and  hypidiomorphic  structure,  in  which  the  shapes 
of  feldspar  crystals  are  recognizable. 

In  the  intermingling  of  rhyolite  and  basalt  on  the  south  side  of  Gardiner 
River,  south  of  Bunsen  Peak,  the  resulting  product  is  quite  the  same  as 
that  just  described.  Most  of  the  rhyolitic  portion,  however,  is  holocrys- 
talline, in  part  microspherulitic.  A  smaller  part  is  glassy.  The  brown 
fibrous  spherulites  exhibit  numerous  dark  arms,  and  are  optically  negative. 


432  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

They  also  contain  delicate  needle-like  prisms  of  augite,  speckled  with 
magnetite  gi'ains.  These  radiate  from  the  center  of  the  spherulite  and  are 
curved  and  forked,  or  branch  into  fern-shaped  grovips,  with  the  branches 
making  an  angle  of  about  36°  with  the  main  stem.  Some  spread  in  fan-like 
forms;  others  branch  at  nearly  90°,  the  branching  prisms  being  different 
lengths.  The  cross  sections  are  those  of  augite  prisms  bounded  by  prism 
faces  and  a  pinacoid.  The  outlines  are  often  indistinct,  as  though  the 
prisms  consisted  of  a  number  of  parallel  crystals.  The  extinction  angle 
reaches  42°. 

It  is  evident,  both  from  the  occuiTeuce  of  large  fragments  of  basalt 
completely  sm-rounded  by  rhyolite  and  from  the  microscopical  chaa-acter 
of  the  rocks,  that  the  rhyolite  fused  the  basalt  and  was  the  more  recent 
eruption.  The  rhyolite  must  have  been  in  a  completely  fused  condition 
when  it  came  in  contact  with  the  basalt,  so  that  its  temperature  was  higher 
than  that  of  the  melting  point  of  basalt.  The  latter  was  not  melted  at  any 
considerable  distance  from  the  contact  with  rhyolite,  but  behaved  as  though 
dissolved  in  the  rhyolitic  magma  along  the  contact. 


CHAPTER    XI. 
RECENT    BASALTS. 


By  Joseph  Paxson  Iddings. 


The  recent  basalts  are  those  that  were  erupted  after  the  extravasation 
of  the  rhyoHte  or  during-  the  period  of  rhyoHtic  eruptions.  They  are  in 
most  cases  distinguishable  from  those  basalts  that  were  associated  with  the 
early  andesitic  breccias,  and  which  have  been  described  in  connection  with 
those  breccias.  They  occur  immediately  overlying  the  rhyolite,  or  inter- 
calated between  rhyolite  sheets,  or  directly  beneath  them,  in  such  a  manner 
as  plainly  to  be  closely  connected  with  them  in  respect  of  the  time  of 
eruption.  In  many  cases  the  basalt  has  been  partially  removed  by  erosion, 
leaving  isolated  patches  and  sheets  scattered  over  the  rhyolitic  plateau. 
Remnants  of  once  extensive  sheets  of  recent  basalt  occur  west  of  the  Gal- 
latin Mountains  and  The  Crags,  overlying  rhyolite.  They  are  scattered 
over  the  plateau  south  and  occur  in  the  broad  valley  of  the  Madison  River. 
These  basalts  are  characterized  by  the  scarcity  or  total  absence  of  noticeable 
phenocrysts.  They  are  mostly  dark  gray  and  porous  or  minutely  vesicular. 
They  are  extremely  fresh  and  unaltered,  and  the  feldspars,  when  large 
enough  to  be  seen  megascopically,  are  brilliant  microtine.  Phenocrysts  of 
microtine  are  sometimes  scattered  sparsely  through  the  rocks.  In  a  very 
few  instances  rounded  grains  of  quartz  were  observed. 

In  a  gray  porous  basalt  with  multitudes  of  minute  feldspars  and 
numerous  briUiaut  phenocrysts  of  microtine,  which  is  found  on  the  ridge 
on  the  northern  side  of  Madison  Plateau  (589),  there  is  a  narrow  streak 
through  the  basalt  of  vesicular  and  perlitic  glass,  which  is  mottled  white 
and  dark  gray.  It  is  apparently  rhyolitic,  and  is  probably  the  result  of  a 
fusion  of  the  two  rocks,  resembling  the  occurrence  of  intermingled  basalt 

-28  433 


434  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

and  rliyolite  found  on  the  plateau  ridge  1  mile  west  of  Beaver  Lake  (1^04 
et  seq.)  and  just  described  in  connection  with  the  rhyolite. 

The  basalt  sheets  along  Gardiner  River,  around  the  base  of  Bunsen 
Peak,  and  at  Osprey  Falls,  and  those  in  tlie  valley  of  Lava  Creek  and  at 
Undine  Falls  and  in  this  vicinity,  occur  partly  overlying  rhyolite,  partly 
beneath  it.  At  Osprey  Falls  there  are  eight  horizontal  sheets  of  columnar 
basalt  directly  overlain  by  a  similar  sheet  of  columnar  rhyolite,  which  m 
turn  is  overlain  by  a  horizontal  sheet  of  columnar  basalt.  Owing  to  the 
dark  color  of  the  surface  of  the  columns  of  rhyolite,  all  of  the  lava  sheets 
appear  alike  when  seen  from  a  short  distance.  The  rhyolite  sheet  is  a  thin 
edge  of  the  great  sheet  of  the  plateau  south.  The  petrographical  character 
of  the  basalts  at  this  place  is  like  that  of  those  just  described — dark  gray, 
with  abundant  minute  feldspars  and  occasionally  larger  ones  of  microtine. 
The  same  is  true  of  the  basalts  in  the  valley  of  Lava  Creek  and  of  those 
at  Undine  Falls.  Here  the  position  of  the  sheets  is  like  that  of  those  at 
Osprey  Falls,  but  their  relation  to  the  rhyolite  is  not  so  plain.  Just  north 
of  this  valley,  along  the  crest  of  the  south  face  of  Mount  Everts,  there  are 
several  exposures  of  basalt  directly  underneath  the  rhyolite  sheet  which 
tops  the  mountain.  The  basalt  is  dark  colored,  vesicular,  and  scoriaceous, 
with  few  small  phenocrysts  of  feldspar  and  pyroxene  (618  to  621).  In 
another  exposure  it  is  more  crystalline  and  vesicular,  with  numerous 
phenocrysts  of  medium-sized  microtine,  and  a  few  of  olivine  (622). 

Remnants  of  basalt  sheets  occur  on  both  sides  of  Yellowstone  Valley 
from  near  Gardiner  to  Broad  Creek,  and  also  up  the  Lamar  Valley.  In 
some  cases  the  time  of  their  eruption,  relative  to  that  of  the  rhyolite,  can 
not  be  learned.  But  in  most  cases  their  position  with  respect  to  other 
formations  is  such  as  to  correlate  them  with  the  recent  basalts.  Petro- 
graphically  also  they  resemble  them. 

In  the  neighborhood  of  Tower  Falls  basalt  forms  a  massive  sheet  rest- 
ing dii'ectly  upon  andesitic  breccia,  and  has  the  kind  of  columnar  structure 
characteristic  of  sui-ticial  lava  streams.  On  the  west  side  of  the  canyon, 
north  of  the  falls,  it  forms  a  vertical  cliif  150  feet  high,  with  beautifully 
developed  columnar  structure,  shown  in  PI.  LVIII.  The  lowest  part  con- 
sists of  dense  basalt,  cracked  into  vertical  columns,  2  to  2  J  feet  wide  and  5 
to  12  or  15  feet  high.  These  merge  upward  through  continuous  rock  into 
small,  slender  columns,  which  curve  slightly  toward  centers  near  the  top  of 


KECENT  BASALTS.  435 

the  cliff,  where  the  basalt  is  vesicular.  The  small  columns  are  3  to  4  inches 
in  diameter.  All  the  columns,  large  and  small,  have  a  wavy  outline,  with 
cross  markings,  like  crude  chiseling.  In  places  the  top  of  the  cliff  projects 
beyond  the  base,  and  sheets  of  small  columns  hang  down  like  curtains. 

The  petrographical  characters  of  these  basalts  is  described  in  a  later 
paat  of  this  chapter.  The  younger  basalts  in  the  valley  of  Lamar  River, 
near  Amethyst,  Soda  Butte,  and  Opal  creeks,  are  dense  and  dark  gray  and 
sometimes  vesicular.  They  are  aphanitic,  rarely  with  small  phenocrysts. 
Similar  basalt  occurs  at  the  mouth  of  Miller  Creek.  In  nearly  all  these 
occurrences  the  basalt  sheets  are  columnar. 

Basalt  covers  the  rhyolite  over  the  bottom  of  Falls  River  Basin.  It 
must  have  formed  a  thin  sheet  of  lava,  for  it  has  been  cut  through  by  the 
drainage  channels,  which  are  for  the  most  part  in  rhyolite.  The  basalt 
forms  ledges  or  low  cliffs  a  short  distance  back  from  the  streams,  in  some 
cases  crossing  them  and  giving  rise  to  waterfalls.  It  seems  to  have  stood 
at  about  the  altitude  of  6,500  feet  around  the  margin  of  the  basin  and  up 
the  canyon  of  Beckler  River.  On  Boone  Creek,  4  miles  above  its  mouth, 
it  is  very  porous  and  also  vesicular,  very  fresh,  purplish  and  steel  gray, 
and  is  filled  with  minute  feldspars  and  some  larger  ones,  also  clusters  of 
feldspars  and  olivine,  which  has  a  submetallic  luster  (1760,  1761).  North 
of  the  mouth  of  Mountain  Ash  Creek  it  is  denser  and  also  vesicular,  is 
gray  and  also  mottled,  and  has  few  phenocrysts  (1757,  1758).  At  Iris 
Falls,  on  Beckler  River,  it  is  dark  gray  and  highly  vesicular,  without  pheno- 
crysts (1759),  the  lower  portion  of  the  flow  being  columnar  in  vertical 
prisms,  30  feet  high.  These  basalts  extend  south  and  southwest  and  consti- 
tute the  great  lava  plains  of  the  Snake  River  Valley  in  Idaho. 

The  recent  basalts  differ  among  themselves  in  habit  and  microstruc- 
ture,  and  some  of  them  resemble  closely  some  of  the  older  basalts;  but 
the  greater  number  of  them  are  distinctly  different  from  the  older  basalts. 
In  general  they  are  dense,  dark  rocks,  almost  free  from  megascopic  pheno- 
crysts. Some  are  partially  ophitic,  and  a  great  number  are  closely  related 
to  these,  but  ai-e  so  fine  grained  that  an  ophitic  structure  has  n'ot  been 
developed.  For  convenience  of  description  they  may  be  classified  under 
the  following  heads: 

(a)  Ophitic. 

(b)  Related  to  ophitic,  but  finer  grained. 


436     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

(c)  Very  fine  grained,  with  small  feldspar  phenocrysts. 
It  must  not  be  forgotten,  however,  that  these  are  often  merely  phases 
of  crystallization  that  may  sometimes  occur  in  one  and  the  same  rock  body. 

OPHITIC   BASALiT. 

The  basalts  with  ophitic  structure  are  very  fine-grained,  holocrystalline 
rocks,  with  very  few  small  phenocrysts  of  lime-soda  feldspar,  in  some  cases 
none.  They  occur  in  all  parts  of  the  Park,  having  been  found  at  a  number 
of  places  on  Yellowstone  River,  in  the  sheet  opposite  Tower  Falls  (661), 
near  Garnet  Hill  (652),  in  the  sheets  at  the  mouth  of  Blacktail  Deer  Creek 
(625),  and  in  those  near  Bear  Gulch  and  elsewhere.  It  is  a  structural  facies 
of  the  basalt  underlying  rhyolite  on  Mount  Everts  (622)  and  occurs  in  the 
basalt  on  the  rhyolite  plateau  (588,  596).  It  also  forms  a  facies  of  the  basalt 
of  Falls  River  Basin  (1758).  The  proportions  of  the  mineral  constituents — 
augite,  labradorite,  olivine,  and  magnetite — vary  in  difi'erent  rocks.  In 
some,  augite  is  in  excess  of  feldspar ;  in  others,  they  are  nearly  equal  to  each 
other.  The  ophitic  augites  range  from  0.5  to  1  mm.  in  diameter,  while  the 
inclosed  feldspars  average  0.1  mm.  in  length.  The  basalt  overlying  gneiss 
on  the  summit  of  Hellroaring  Peak,  just  north  of  the  Park  boundary  (658), 
has  the  greatest  amount  of  augite  and  magnetite  and  rod-shaped  iron  oxide 
(ilmenite  f),  with  subordinate  labradorite  and  olivine.  The  olivine  is  in 
small,  nearly  idiomorphic  crystals,  and  also  in  a  few  small  phenocrysts, 
besides  a  few  of  labradorite.  A  basalt  from  the  plateau  southwest  of  the 
Gallatin  Mountains  (588)  is  similar,  but  the  labradorite  is  more  abundant, 
and  olivine  in  minute  crystals,  slightly  reddened  on  the  surface,  is  very 
abundant.  Augite  and  magnetite  are  plentiful.  There  are  no  megascopic 
phenocrysts.  Others  are  similar,  but  are  finer  grained.  In  one  case  (1041) 
augite  and  labradorite  (about  Aug  Aba)  are  in  nearly  equal  proportions,  and 
magnetite  and  olivine  are  less  than  in  the  two  previous  cases.  There  are 
no  megascopic  phenocrysts.  This  structure  is  shown  in  PI.  LIX,  fig.  1. 
The  basalt  from  north  of  the  mouth  of  Mountain  Ash  Creek,  Falls  River 
Basin  (1758),  is  like  the  last  in  composition,  but  has  small  phenocrysts  of 
long  prismatic  labradorite  and  olivine.  These  four  rocks  are  almost  per- 
fectly fresh,  and  are  holocrystalline,  with  numerous  small  pores.  The  basalts 
occurring  near  Junction  Butte  and  opposite  Tower  Fall  (652,  654,  661)  are 
also  holocrystalline,  but  have  relatively  more  labradorite  in  tabular  crys- 


U.   8.   OEOLOOICAL  AUnvF 


MONOORAPH  XXXH      PART  II      PL.    Lvlli 


COLUMNAR   STRUCTURE,    YELLOWSTONE    CANYON, 


U.  S.  OEOLOQICAL    SURVEY 


MONOGRAPH    XXXII     PART    M     PL.   LIX 


(  B)  X   3  5 
PHOTOMICROGRAPHS    OF    BASALT 


THE  HELfOTVPE  PRINTING  CO.,  BOSTON 


OPHITIC  STRUCTURE.  437 

tals,  with  not  so  high  double  refraction  as  in  the  previous  rocks.  There  is 
serpentine,  resuUing  from  the  partial  alteration  of  olivine.  The  iron  oxide 
is  mostly  in  rod-like  crystals.  The  ophitic  form  of  the  basalt  beneath 
rhyolite  on  Mount  Everts  (622)  is  like  the  first  ophitic  basalts  in  composi- 
tion. The  augite  is  about  the  same  size,  but  the  labradorite  pi'isms  ai-e 
larger,  and  there  is  considerable  globulitic  and  microlitic  glass  base  scattered 
through  the  mass.  Olivine  is  abundant  in  microscopic  crystals.  A  few 
labradorites  form  phenocrysts.  The  rock  is  full  of  irregular  cavities.  The 
top  sheet  of  basalt  near  the  mouth  of  Bear  Grulch,  east  of  Gardiner,  and 
another  basalt  flow  in  this  vicinity,  are  like  the  last  one,  but  in  these  there 
is  an  approach  to  a  parallel  arrangement  of  the  feldspar  prisms  inclosed  in 
the  augite  crystals  (PI.  LIX,  fig.  2). 

BASALTS  RELATED  TO  THOSE  WITH  OPHITIC  STRUCTURE. 

These  basalts  resemble  those  just  described  in  mineral  composition  and 
in  the  character  of  the  minerals,  except  that  augite  occurs  in  smaller  crystals 
and  grains,  and  not  in  relatively  large  micropoikilitic  ones.  Augite  occupies 
about  the  same  spaces  as  when  it  takes  part  in  ophitic  structure,  but  is  in 
aggregates  of  small  crystals.  Olivine  and  magnetite  are  the  same  as  in  the 
ophitic  rocks.     There  is  a  small  amount  of  microlitic  glass  base. 

Another  modification  of  the  basalt  beneath  the  rhyolite  on  Moimt 
Everts  (623),  and  a  vesicular  basalt  from  the  northern  base  of  Prospect 
Peak  (634),  are  finer-grained  rocks,  hke  the  ophitic  form  of  the  finst- 
mentioned  basalt  in  composition,  but  with  only  a  part  of  the  augite  inclosing 
labradorite,  and  thus  being  partly  ophitic,  the  remainder  of  the  augite  being 
in  small  allotriomorphic  grains  between  idiomorphic  feldspars.  The  ferro- 
magnesian  minerals  are  in  excess  of  feldspar,  and  magnetite  is  abundant. 
The  chemical  composition  of  the  basalt  from  the  north  base  of  Prospect 
Peak  (634)  is  shown  by  the  following  analysis.  In  this  rock  lime  is  con- 
siderably higher  than  magnesia,  and  soda  is  greatly  in  excess  of  potash. 


438 


GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 
Analysis  of  basalt  from  the  north  base  of  Prospect  Peak. 


Constituent. 


SiOa 

TiOj 

AI.2O3 

FejOj 

FeO 

MnO 

MgO 

CaO 

NajO 

K2O 

P2O6 

SO3 

LiiO 

HjO 

Total 


Per  cent. 


48.49 

2.19 

18.35 

7.63 

1.21 

None. 

6.72 

10.40 

3.02 

.57 

.20 

.52 

.02 

.67 


99.99 


The  basalt  from  another  exposure  on  Mount  Everts  (618)  and  one  from 
Falls  River  Basin  (1757)  have  a  little  ophitic  augite  and  much  that  is  in 
grains.  It  is  in  excess  of  feldspar.  A  basalt  from  the  south  side  of  Lava 
Creek  below  Undine  Falls  (613)  is  richer  in  feldspar  and  the  olivine  is 
altered;  otherwise  it  is  similar  to  the  basalts  just  described.  The  basalt 
from  4  miles  above  the  mouth  of  Boone  Creek  (1739)  and  one  from  the 
Snake  River  Valley  (1760,  1761)  have  no  ophitic  augite,  but  the  prismatic 
labradorite  is  idiomorphic  and  the  general  character  of  the  rock  is  the  same 
as  that  of  those  just  described;  there  is,  however,  considerable  microlitic 
base,  and  ilmenite  rods  are  numerous.  Olivines  are  small,  and  the  dark- 
colored  minerals  are  in  excess  of  the  feldspar.  The  basalt  from  Iris  Falls, 
Bechler  River  (1759),  is  very  fine  grained  and  partly  ophitic,  with  minute 
feldspar  phenocrysts. 

The  basalt  o-verlying  dacite-porphyry  east  of  Bunsen  Peak  (606)  is 
very  much  like  the  ophitic  basalts.  The  lath-shaped  labradorite  is  similar 
to  that  in  the  foregoing,  but  in  places  shows  a  slightly  parallel  arrange- 
ment. Basalts  from  numerous  localities  in  the  Park  (582,  584,  589,  591, 
598,  603,  614,  615,  624,  627,  632,  655,  663,  671)  are  quite  the  same  as  the 
one  last  mentioned,  but  vary  slightly  in  the  relative  proportions  of  augite 
and  feldspar  and  in  the  size  of  the  component  crystals.  All  are  holocrystal- 
line,  or  nearly  so.     In  some  modifications  of  these  rocks  (605,  614)  the 


FINE  GRAINED  BASALTS.  439 

labradorite  prisms  are  more  nearly  parallel,  with  fluidal  arrangement  (PI. 
XXXIV,  fig.  4).  Some  of  the  phenocrysts  of  labradorite-bytownite  are 
almost  free  from  polysynthetic  twinning,  having  but  two  or  three  parts. 
Others  (597,  612,  1139)  are  nearly  the  same,  with  small  grains  or  crystals. 
And  still  others  (593,  610,  611,  636,  1138,  1141)  are  like  the  last,  but  con- 
tain more  augite  than  feldspar. 

VERY  FINE-GRAINED  BASAIiTS  WITH  MINUTE  PHENOCRYSTS. 

In  the  still  finer-grained  modifications  of  these  basalts,  which  are  very 
numerous,  the  lath-shaped  or  prismatic  labradorite  crystals  range  in  size 
from  about  1  mm.  long  to  extremely  minute  microlites.  They  are  in  a  mass 
of  magnetite  grains  and  minute  augite  grains  or  crystals,  sometimes  with 
brown  glass  base,  as  in  the  coarser-grained  forms,  some  resembling  the 
foregoing  rocks  in  microstructure  (581,  616,  626,  662,  1140).  The  average 
length  of  the  labradorite  prisms  is  0.06  mm.  Even  in  thin  section  they  are 
very  dark  gray.  When  still  less  crystalline  they  are  darker,  being  nearly 
black  in  thin  section.  There  is  more  microlitic  glass  base,  which  is  crowded 
with  grains  of  magnetite,  some  forming  skeleton  aggregates  of  the  usual 
stellate  or  cruciform  shapes  (619,  637,  653,  660).  One  variety  from  beneath 
the  rhyolite  sheet  on  Mount  Everts  (621)  has  an  almost  panidiomorphic 
structure,  the  augites  being  in  minute  prisms.     Olivine  is  scarce. 

A  modification  of  the  fine-grained  stnicture  with  feldspar  prisms  of 
nearly  uniform  size  is  one  in  which  many  small  prisms  of  labradorite  are 
in  a  groundmass  of  minute  grains  of  magnetite  and  augite,  about  0.01mm. 
in  diameter,  and  olivine  also  forms  small  phenocrysts  (594,  607,  609,  638,  639, 
666).  The  finest-grained  form  consists  of  a  groundmass  of  grains  of  mag- 
netite and  augite  0.004  mm.  in  diameter,  and  very  minute  feldspars,  with 
many  small  phenocrysts  of  labradorite  and  olivine,  about  0.5  mm.  in  length 
and  smaller  (586,  587,  599,  1796). 

In  all  of  these  69  recent  basalts,  with  the  single  exception  of  the  few 
almost  microscopic  augites  in  a  basalt  on  Gardiner  River,  south  of  Bunsen 
Peak  (1796),  no  augite  phenocrysts  occur.  The  most  usual  ones  are  labra- 
dorite, and  less  often  olivine.  In  most  cases  there  are  no  distinct,  mega- 
scopic phenocrysts.  Moreover,  none  of  these  basalts  possess  andesitic 
structure.  If  more  coarsely  crystallized,  they  would  probably  have  all  be- 
come ophitic. 


CHAPTER     XII. 

PALEOZOIC    FOSSILS. 

Section  I.— CAMBRIAN  FOSSIIiS. 


By  Charles  Doolittle  Walcott, 


The  Cambrian  fauna  of  the  Park  includes  10  species  that  are  referred 
to  the  upper  division,  and  21  that  are  referred  to  the  middle  and  lower 
divisions,  of  the  Middle  Cambrian  fauna.  Of  these,  Acrofrcfa  gemma  is 
common  to  the  upper  and  middle  divisions.  The  Middle  Cambrian  fauna 
includes  the  following  species: 

Haguia  sphrerica. 

Obolus  (Liugulepis)  acuminatus  var.  meeki. 

Iphidea  sculptilis. 

Iphidea  (sp.  uudet.). 

Acrotreta  gemma. 

Platyceras  primordialis. 

Hyolitbes  primordialis. 

Agnostns  bidens. 

Agnostus  iuterstrictus. 

Agnostus  tumidosus. 

Ptychoparia  penfieldi, 

Ptycboparia  antiquata. 

Ptycboparia  (sp.  uudet.). 

Crepicephalus  texanus. 

Ptycboparia  (Loncbocepbalus)  bamiilus  1 

Ptychoparia  (Loncbocepbalus)  wiscoDsensis. 

Ptycboparia  ( ?)  diademata. 

Arionellus  (sp.  undet.). 

Liostracus  parvus. 

Solenopleura  weedi. 

Zacantboides  (sp.  undet.). 

Batbyuriscus  ?  (sp.  undet.). 

This  fauna  is  more  intimately  related  to  that  of  the  Black  Hills  and 
the  Upper  Mississippi  Valley  in  Wisconsin  and  Minnesota  than  to  the  Middle 

440 


CAMBRIAN  FOSSILS.  441 

Cambrian  fauna  of  Nevada  or  liritish  ^Columbia.  There  are  no  indications 
of  the  Lower  Cambrian  or  Olenelhis  fauna.  The  upper-division  fauna  is 
also  strongly  related  in  its  Brachiopoda  to  the  Mississippi  Basin  fauna.  It 
includes  the  following  species: 

Obolus  (Liugulella)  desideratus. 
Dicellomus  nanus. 
Billingsella  coloradoensis. 
Orthis  remnicha. 
Orthis  sandbergi. 
Ptychoparia  (E.)  afflnis. 
Ptychoparia  llanoensis  ? 
Ptychoparia  (sp.  undet.). 
Arionellus  levis. 

The  species  common  to  the  Cambrian  fauna  of  the  Park  and  the  Upper 
Mississippi  Valley  are  as  follows: 

Billingsella  coloradoensis. 

Orthis  remnicha. 

Orthis  sandbergi. 

Platyceras  priuiordialis. 

Hyolithes  iirimordialis. 

Ptychoparia  (Louchocephalus)  hamulus  ? 

Ptychoparia  (Lonchocephalus)  wisconsensis. 

Ptychoparia  ( 1)  diademata. 

Of  Other  species,  Agnostus  hidens  and  Agnostus  interstrictus  are  closely 
related  to  A.  josepha,  and  it  is  quite  probable  that  Dicellomus  nanus  and 
Ptychoparia  antiquata  will  be  found  in  the  Upper  Mississippi  Valley  fauna. 

Billingsella  coloradoensis,  Orthis  remnicha,  and  Crepicephalus  texanus  are 
found  in  the  Cambrian  rocks  of  central  Texas,  and  Ptychoparia  antiquata  and 
Crepicephalus  texanus  occur  in  the  Middle  Cambrian  of  northern  Alabama. 

It  is  anticipated  that  a  large  addition  will  be  made  to  this  fauna  when 
the  Cambrian  collections  from  the  Gallatin  Valley  north  of  the  Yellowstone 
National  Park  are  studied.  The  purpose  of  this  paper  is  to  describe  and 
illusti-ate  only  the  species  found  within  the  limits  of  the  Park  and  the 
immediately  adjoining  Absaroka  Range  on  the  east. 

Preliminary  examinations  of  the  collections  were  made  from  year  to 
year  as  the  specimens  were  brought  from  the  field  and  reports  were  made 
to  Mr.  Arnold  Hague.  When  it  was  found  possible  to  make  a  detailed  study, 
I  requested  Mr.  G.  H.  Girty  to  prepare  the  brachiopods  contained  in  the  col- 
lection, and  I  am  indebted  to  him  for  assistance  rendered  in  this  du-ection. 


442     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

DESCRIPTIONS  OF  GENERA  AND  SPECIES. 

CAMBRIAN. 
HAGUIA  n.  gen. 

Spherical  bodies  without  any  central  axis  or  opening;  with  irregular 
lacuna^  or  canals  separated  by  irregular  walls  of  varying  thickness  that 
are  built  up  of  minutely  granular  carbonate  of  lime.  The  outer  wall  is 
perforated  by  the  apertures  of  the  numerous  canals. 

The  genus  is  based  on  small  spheroidal  bodies  that  occur  on  slabs  of 
limestone  scattered  among  the  fragmentary  remains  of  trilobites  (Pfycho- 
paria  (L.)  wisconsensis,  P.  (?)  diademata)  and  the  two  valves  of  Billingsella 
^oepina.  The  transverse  sections  recall  at  once  sections  of  Protopliaretra 
densa  Bornemann,^  but  there  is  no  central  axis  or  cavity.  Dr.  Bornemann 
regards  Protopharetra  as  a  lower  stage  of  development  of  Archseocyathus 
forms,  but  Dr.  Hinde  is  inclined  to  consider  it  as  a  distinct  generic  type.^ 
The  form  now  under  consideration  is  clearly  distinct  from  the  cup-shaped 
and  branching  forms  of  the  Archjfeocyathinse  and  evidently  the  simplest 
type  of  the  family.  In  fact,  were  it  not  for  the  absence  of  spicules  and  the 
presence  of  a  canal  system,  somewhat  like  that  of  Protopharetra  densa, 
I  should  refer  it  at  once  to  the  sponges  It  is  on  the  border  land  between 
the  corals,  as  represented  by  the  Archajocyathinse,  and  the  sponges,  with  a 
tendency  to  the  latter,  which  would  have  placed  it  among  them  previous 
to  Dr.  Hinde's  studies. 

Haguia  sph^rica  u.  sp. 

PI.  LXIII,  figs.  6,  6a. 

Small  spherical  bodies,  varying  from  2  to  8  mm.  in  diameter,  formed 
of  minutely  granular  carbonate  of  lime.  The  irregular  laminae  or  canals 
are  filled  with  crystalline  calcite.  The  canals  penetrate  the  outer  wall 
and  give  the  outer  surface  a  roughened  appearance,  owing  to  the  irregular 
disposition  of  the  openings.  In  one  section  there  is  a  rough  radial  arrange- 
ment of  the  canals,  but  in  several  others  there  is  no  trace  of  any  regularity. 

'  Nova  Acta,  Leop.-Carol.  Deutscher  Akad.  Naturforscher,  Vol.  LI,  Pt.  I,  1886,  PI.  VIII,  fig.  8. 
=  Quart.  Jour.  Geol.  Soc.  London,  1889,  Vol.  XLV,  p.  136. 


CAMBRIAN  FOSSILS.  443 

Formation  and  locality  :  Middle  Cambrian,  Flathead  formation  ;  north 
side  of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  and  Soda 
Butte  creeks,  Yellowstone  National  Park. 

OBOLUS  Eichwald. 

Subgenus  LINGULEPIS  Hall. 

Lingidepis  Hall,  1863:  Sixteenth  Ann.  Kept.  New  York  State  Cab.  Nat.  Hist.,  p.  129. 

Lingulepis  Meek  and  Hayden,  1864:  Pal.  Upper  Missouri,  Pt.  I,  p.  1. 

Lingvlepis  Hall,  1867 :  Trans.  Albany  Institute,  Vol.  V,  p.  106. 

Lingulepis  Hall  and  Clarke,  1892:  Eleventh  Ann.  Kept.  State  Geologist  New  York 

(author's  ed.),  p.  231,  PI.  I,  figs.  16,  17. 
Lingulepis  Hall  and  Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  pp.  59, 163. 
Lingulepis  Walcott,  1897 :  Am.  Jour.  Sci.,  4th  series.  Vol.  Ill,  p.  404. 
Type,  Lingula  acuminata  Conrad  sp.  =  Lingula  pinniformis  Owen. 

A  comparison  of  a  series  of  specimens  of  Oholus  (Lingulepis)  acumi- 
natus  from  the  Potsdam  terrane  and  the  base  of  the  Calciferous  formation 
of  Saratoga,  Washington,  Franklin,  and  Jefferson  counties.  New  York,  and 
from  the  same  horizons  in  Ontario,  Canada,  with  a  large  series  of  speci- 
mens from  the  St.  Croix  sandstone  of  Wisconsin,  leads  to  the  conclusion  that 
Obolus  (Lingulepis)  pinniformis  is  a  synonym  of  Obolus  (Lingulepis)  acumi- 
natiis.  This  makes  Obolus  (Lingulepis)  acuminatus  the  type  of  the  subgenus 
Lingulepis,  the  original  description  of  the  genus  being  based  upon  speci- 
mens from  the  St.  Croix  sandstone  of  Wisconsin. 

The  further  study  of  the  types  of  the  species  that  have  been  referred 
to  Lingulepis  results  in  the  elimination  of  all  of  them  from  the  subgenus 
with  the  exception  of  Obolus  (Lingulepis)  acuminatus  and  its  variety  meeU. 

Th«  species  that  have  been  referred  to  Lingulepis  heretofore  are  now 
referred  as  follows : 

Lingulepis  dakotaensis  M.  and  H.  =  Obolus  (Lingulepis)  acuminatus. 
Lingulepis  pinniformis  Owen  =  Obolus  (Lingulepis)  acuminatus. 
Lingulepis  minima  Whitfield  =  Obolus  (Lingulepis)  acuminatus. 
Lingulepis  perattenuata  Whitfield  =  Obolus  (Lingulella)  perattenuatus. 
Lingulepis  cuneolus  Whitfield  =  Obolus  (Lingulella)  cuneolus. 
Lingulepis  ella  H.  and  W.  =  Obolus  (Lingulella)  ella. 
Lingulepis  matiualis  Hall  =  Obolus  (Lingulella)  matinalis. 
Lingulepis  maera  H.  and  W.  =  Obolus  (Lingulella)  majra. 
Lingulepis  ?  minuta  H.  and  W.  =  Obolella  minuta. 
Lingulepis  morsensis  Wiuchell  (Miller)  =  Lingula  morsii. 
Lingulepis  prima  M.  and  H.  =Dicellomus  politus. 


444  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

In  a  review  of  the  Cambrian  Brachiopoda,  now  being  prepared,  the 
Cambrian  species  referred  to  the  subgenus  Lingulepis  will  be  fully  illus- 
trated. 

Obolus  (Lingulepis)  aouminatus  var.  meeki  Walcott. 

PL  LX,  figs.  1,  ifl. 
Lingulepis  meeki  Walcott,  1897 :  Am.  Jour.  Sci.,  4th  series.  Vol.  Ill,  p.  405. 

Shell  small,  attenuate,  marked  by  rather  strong  concentric  lines  and 
strise  of  growth,  and  by  interrupted  irregular  radiating  striae. 

Ventral  valve  narrow,  elongate;  beak  acuminate,  rostral  slopes  long, 
nearly  straight,  passing  gradually  into  the  curvature  of  the  anterolateral 
margins,  and  posteriorly  meeting  at  a  very  acute  angle;  front  strongly 
rounded.  Lenth  of  valve,  8  mm.;  width,  3.5  mm.,  the  widest  portion  being 
near  the  anterior  extremity.  Beak  slightly  upcurved,  the  longitudinal 
median  line  straight,  or  even  slightly  concave  from  the  apex  of  the  beak  to 
the  middle,  where  it  begins  to  slope  gently  to  the  frontal  margin;  trans- 
verse curvature  very  slight  anteriorly,  more  convex  near  the  beak. 

Dorsal  valve  more  convex  than  the  ventral,  hnguliform;  beak  depressed, 
bluntly  rounded,  curving  evenly  and  gradually  to  the  semitruncate  anterior 


margm. 


The  interior  markings  of  this  shell  have  not  been  ascertained,  but  the 
external  characters  are  such  as  to  make  a  reference  to  the  genus  Lingulepis 
more  than  probably  correct.  The  flat  acute-acuminate  ventral  valve,  with 
its  elevated  or  retrorse  beak,  which  is  not  covered  by  the  smaller  dorsal 
shell,  is  pecuharly  characteristic  of  Lingulepis. 

There  is  a  form  from  Texas,  probably  identical  with  Oholiis  (Lingiilella) 
perattenuatus,  that  might  be  mistaken  for  this  species,  but  it  is  an  undoubted 
Linffulella,  and  does  not  show  the  external  characteristics  of  Lingulepis.  A 
comparison  with  the  young  and  narrow  specimens  of  0.  (L.)  aciiminatus 
shoAvs  it  to  be  clearly  distinct  from  that  species;  the  posterior  rostral  slopes 
of  0.  (L.)  acuminatus  possess  a  pecuhar  incur%ang  which  is  not  shown  in 
the  variety  meeki. 

Formation  and  locaUty:    Middle  Cambrian,  upper  beds  of  Flathead 
ten-ane,  Crowfoot  section,  Gallatin  Range,  Yellowstone  National  Park. 


CAMBRIAN  FOSSILS.  445 

OBOLUS  Kichwald. 

Subgenus  LINGULELLA  Salter. 

Obolus  (Lingulella)  desideratus  Walcott. 

PI.  LX,  figs.  2,  2a. 

Obolus  {Lingulella)  desideratus  Walcott,  1S98 :  Proc.  U.  S.  Nat.  Mus.,  Vol.  XXI,  p.  399. 

Shell  small,  subovate,  with  the  ventral  valve  obtusely  acuminate,  and 
the  dorsal  valve  broadly  ovate.  Valves  are  strongly  convexed,  with  the 
ventral  valve  fully  as  much  so  as  the  dorsal.  There  is  a  little  variation  in 
the  outline  of  the  valves,  some  being  slightly  more  roiinded  posteriorly 
than  others. 

The  surface  of  the  shell  is  marked  by  fine,  concentric  lines  of  growth 
and,  between  them,  very  fine,  slightly  irregular  striae.  A  few  rather  narrow 
indistinct  undulations  radiate  from  the  umbo  toward  the  front  and  lateral 
margins.  When  the  outer  shell  is  partially  exfoliated  the  outer  surface  of 
the  inner  layer  is  marked  by  very  fine  indistinct  radiating  striae.  There 
are  a  few  traces  of  small,  scattered  pits  or  punctae  on  the  inner  surface  of 
the  shell.  The  shell  is  thin  and  is  formed  of  an  outer  layer  and  one  or 
more  inner  layers  or  lamellae. 

The  average  length  of  the  ventral  valve  is  about  4  mm. ;  width,  3  mm. 
A  dorsal  valve  3.5  mm.  long  has  a  width  of  3  mm. 

A  cast  of  the  interior  of  a  dorsal  valve  shows  an  area  of  medium 
length,  divided  midway  by  a  narrow,  clearly  defined  pedicle  groove.  The 
area  of  the  dorsal  valve  is  short.  Nothing  is  known  of  the  interior  of  the 
ventral  valve,  but  in  a  cast  of  a  dorsal  valve  may  be  seen  traces  of 
the  main  vascular  sinuses  and  central  median  ridge,  and  of  the  central 
muscle  scars.  > 

Observations. — Tliis  spccies  from  the  Upper  Cambrian  may  be  compared 
with  the  Middle  Cambrian  0.  (L.)  ferrugineus  of  the  Atlantic  Basin  fauna. 
Compared  with  the  Rocky  Mountain  species  it  is  intermediate  between  0. 
(i.)  manticiilus  and  0.  (L.)  rotundatus.  It  may  also  be  compared  with  0. 
(i.)  granvillensis  of  eastern  New  York,  upper  Olenellus  fauna. 

What  appears  to  be  an  identical  species  also  occurs  in  the  upper  beds 
of  the  Secret  Canyon  shale  just  beneath  the  Hambm-g  limestone,  1,200 
feet  lower  in  the  Eureka  district  Cambrian  section. 


446     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Formation  and  locality:  Upper  Cambrian,  Gallatin  limestone,  Crow- 
foot section,  Grallatin  Range,  Yellowstone  National  Park;  Hamburg  shale 
near  Hamburg  mine,  Eureka  district,  Nevada.  A  variety  also  occurs  in 
the  Secret  Canyon  shale  1,200  feet  below  the  Hamburg  shale. 

DICELLOMUS  Hall. 

Dicellomus  Hall,  1873 :  Twenty- third  Ann.  Kept.  New  York  State  Cab.  Nat.  Hist.,  p.  246. 
Obolella  Hall,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  p.  72. 

When  proposing  that  the  genus  Dicellomus  include  Obolella  polita,  Pro- 
fessor Hall  stated  that  the  grooving  or  emargination  ot  the  apices  of  both 
valves  and  the  thickening  of  the  edges  of  the  shell  on  each  side  below  the 
apex,  together  with  the  form  and  character  of  the  muscular  impressions, 
would  separate  the  species  from  Obolella.  Again,  in  1892,  Messrs.  Hall  and 
Clarke  gave  a  fuller  description  of  Dicellomus  politus,  but  owing  to  the  poor 
character  of  the  material,  he  did  not  feel  confident  that  it  should  be  recog- 
nized as  generically  distinct  from  Obolella  chromatica.  Material  now  in  the 
collections  of  the  Greological  Survey  clearly  shows  that  Professor  Hall's 
provisional  conclusion  was  correct,  and  that  Dicellomus  ])olitus  is  generically 
distinct  from  Obolella  chromatica.  The  generic  characters  are  also  finely 
shown  by  specimens  of  Dicellomus  nana  (M.  and  H.)  from  the  Little  Rocky 
Mountains  of  Montana,  and  also  by  the  interior  of  the  ventral  valve,  figured 
by  Meek  and  Hayden.  The  cast  of  the  interior  of  the  ventral  valve 
is  shown  by  fig.  3c,  PI.  LX,  and  the  interior  of  the  ventral  valve  from 
the  Black  Hills  by  fig.  M,  PI.  LX.  These  will  be  found  to  differ  from  the 
illustrations  of  Obolella  polita  given  by  Professor  Hall,'  but  the  material 
fx'om  which  the  figures  were  drawn  was  poor,  and,  to  a  certain  extent,  the 
drawings  are  somewhat  constructive,  as  stated  by  Professor  Hall.^  From 
the  specimens  before  me,  as  shown  by  figs.  4,  4a,  PI.  LX,  it  is  clear  that 
Dicellomus  politus  and  D.  nanus  are  congeneric.  Further  illustrations  of 
the  characters  of  D.  politus  will  be  given  in  a  review  of  the  Cambrian 
Brachiopoda. 

1  Sixteenth  Ann.  Rept.  New  York  State  Cab.  Nat.  Hist.,  1863,  PI.  VI,  figs.  20, 21. 
»Pal.  New  York,  Vol.  VIII,  PI.  I,  p.  72. 


GAM  BRIAN  FOSSILS.  447 

DiCELLOMus  NANUS  M.  and  H.  sp. 
PI.  LX,  figs.  ,3,  3a-d. 

Obolella  nana  Meek  and  Hayden,  1861 :  Proc.  Acad.  Nat.  Sci.  Philadelphia,  2d  series, 
Vol.  V,  i>.  435.  T?illings,  18G2:  Paleozoic  Fossils,  Vol.  I,  p.  07.  Hayden,  1863: 
Am.  Jour.  Sci.,  2d  series.  Vol.  XXXIII,  p.  73.  Meek  and  Hayden,  1864:  Pal. 
Upper  Missouri,  Pt.  I,  p.  4,  PI.  I,  figs.  3a-d.  Whitfield,  1880 :  U.  S.  Geog.  and 
Geol.  Surv.  Rocky  Mountain  Region,  p.  340,  PI.  II,  figs.  14-17.  Hall  and  Clarke, 
1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  p.  69. 

Only  a  single  specimen  of  the  outer  surface  of  a  ventral  valve  of  this 
species  occurs  in  the  collection.  It  has  the  characteristic  appearance  of 
the  species.  The  species  also  occurs  in  abundance  in  the  Little  Rocky 
Mountains  to  the  north,  in  Montana,  and  also  to  the  eastwai'd  in  the  Black 
Hills. 

The  specimen  from  the  Park  is  illustrated,  and,  in  addition,  the  types 
from  the  Black  Hills  and  two  specimens  from  the  Little  Rocky  Mountains. 

Formation  and  locality:  Upper  Cambrian,  Gallatin  limestone  (upper 
portion);  Crowfoot  section,  Gallatin  Range,  Yellowstone  National  Park. 

IPHIDEA  Billings. 

Iphidea  sculptilis  Meek. 

PI.  LX,  figs.  5,  5a-e. 

Iphidea  (??)  sculptilis  Meek,  1873:  Sixth  Ann.  Rept.  U.  S.  Geol.  and  Geog.  Surv.  Terr., 

for  the  year  1872,  p.  479. 
Kutorgina  minutissima  Hall  and  Whitfield,  1877:  U.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV, 

p.  207,  PI.  I,  figs.  11,  12. 
Kutorgina  sculptilis  Walcott,  1884:  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  20,  PI.  I,  figs. 

7,  la-h;  PI.  IX,  fig.  7. 

In  the  description  of  Iphidea  (!?)  sculptilis,  Mr.  Meek  decided  that,  as 
the  shell  had  a  very  narrow,  slightly  flattened  margin  on  each  side,  repre- 
senting a  false  area,  and  as  there  seemed  to  be  a  wide,  open,  triangular 
foramen,  it  could  not  be  referred  to  the  genus  Acrotreta  or  the  genus 
Iphidea.  He  was  not  jjositive  that  there  was  not  a  permanent  pseudo- 
deltidium  present,  but,  assuming  the  absence  of  that  structure,  and  with  the 
probability  that  when  all  the  characters  of  the  shell  were  known  it  would 
be  found  to  belong  to  a  different  genus,  either  of  the  Brachiopoda  or  of 
some  other  group,  he  would  propose  for  the  genus  the  name  "  Micromitra." 


448  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

A  study  of  the  material  collected  from  tlie  same  horizon  at  a  point  not 
far  distant  from  the  original  locality  shows  the  presence  of  a  false  area  and 
a  pseudo-deltidium  of  the  same  character  as  that  of  Iphidea  hella,  the  type 
of  the  genus  Iphidea.  There  is,  however,  a  difference  in  the  two  forms  that 
might  possibly  be  considered  of  subgeneric  value.  The  surface  of  Iphidea 
hella  is  covered  with  fine  concentric  strise,  while  the  surface  of  Iphidea 
sculptilis  is  marked  by  very  fine,  sharp,  elevated,  concentric  lines  that 
coalesce  or  bifurcate  irregularly,  imparting  a  peculiarly  interrupted  wavy 
appearance  that  is  highly  characteristic.  The  variation  in  the  surface 
character  is  continued  still  further  in  Iphidea  piannula  White,  in  which  the 
surface  is  marked  by  a  very  fine  network  of  oblique  raised  lines  that  divide 
it  into  minute  porelike  pits,  which  cause  it  to  resemble  under  the  lens 
the  texture  of  finely  woven  cloth.  The  difference  in  character  of  surface 
between  Iphidea  p)ammla  and  /.  sculpUUs  is  the  same  difference  as  between 
the  surface  characters  of  Trematis  and  Lingulella;  and  the  difference  in 
surface  characters  between  the  two  species  mentioned,  on  the  one  hand, 
and  Iphidea  hella  and  I.  labradorica,  on  the  other  hand,  is  equally  important, 
as  the  latter  have  the  plain  concentric  strise  and  lines  of  growth  that  are 
characteristic  of  the  species,  while  the  former  have  highly  ornamented  sur- 
faces. If  we  should  find  the  genus  on  the  surface  characters  of  the  shell,  it 
would  be  necessary  to  place  I  hella,  I.  lahradorica,  and  J.  prospectensis  under 
one  genus,  I.  ornatella  (Linnarsson)  and  /.  sculptilis  under  another,  and 
I.pannula  and  I.  cailata  under  still  another.  There  are,  however,  specimens 
of  I.  pannula  on  which  the  outer  portions  of  the  shell  show  the  surface 
characters  of  J.  hella;  and  more  or  less  complete  transitions  may  be  found 
between  the  varying  types  of  surface  ornamentation. 

There  are  too  many  similarities  in  form  to  warrant  us  in  removing 
I.  sculptilis  from  Iphidea  without  the  evidence  of  interior  markings  to  prove 
that  it  is  generically  distinct. 

Formation  and  locality:  Middle  Cambrian,  Flathead  terrane  (lowest 
fossiliferous  bed) ;  Crowfoot  section,  Gallatin  Range,  Yellowstone  National 
Park.  It  also  occurs  in  the  Middle  Cambrian  shales  of  Antelope  Springs, 
Utah. 


CAMBRIAN  FOSSILS.  449 

Iphidea  sp.  uiitlet. 
PI.  LX,  lif;-.  (;. 

Dorsal  valve  semicircular,  slig-htly  convex.  Hin^e  line  somewhat 
shorter  than  the  width  of  the  shell  below;  nearly  straight,  tlie  rostral  angle 
about  180°.  Beak  small,  not  elevated.  Surface  ornamentation  consists  of 
extremely  tine  i-adiating  and  undulating  concentric  striai  that  can  be  seen 
in  detail  only  with  a  strong  magnifying  glass.     Shell  substance  horny. 

This  form  is  associated  with  /.  scidptilis,  and,  judging  from  external 
characters,  is  closely  related  to  it.  The  sui-face  ornamentation  is  of  the 
same  character,  and,  in  the  absence  of  the  ventral  valve,  it  is  difficult  to 
distinguish  any  specific  characters  on  which  to  base  a  new  species,  although 
the  shell  is  much  larger  than  that  of  typical  t.  sciilpt'tlis. 

Formation  and  localitj^:  Same  as  last,  for  Ipliidea  scidptilis. 

ACROTRETA  Kutorga. 

ACROTRETA    GEMMA    BilliugS. 

PI.  LXII,  figs.  2,  2a-e. 

Acrotreta  gemma  Billings,  1865:  Pal.  Foss.,  Vol.  I,  p.  216,  figs.  201«-/: 

Acrotreta  subconica  Meek,  1873:  Sixth  Ann.  Kept.  U.  S.  Geol.  Surv.  Terr.,  p.  463. 

Acrotreta  attenuata  Meek,  1S7 3:  Ibid.,  p.  463. 

Acrotreta  pihridicida  White,  1874:  Geog.  and  Geol.  Expl.  Surv.  W.  100th  Merid.: 

Prelim.  Eept.,  Invert.  Foss.,  p.  9.    White,  1875:  Ibid.,  Final  Kept.,  Vol.  IV, 

p.  53,  PI.  Ill,  flgs.  3a-d. 
Acrotreta  gemma  Walcott,  1884 :  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  17,  PI.  I,  figs. 

Irt,  h,  d,f;  PI.  IX,  flgs.  9,  9a.     Walcott,  1886:  Bull.  U  .S.  Geol.  Surv.  No.  30, 

p.  98,  PI.  VIII,  flgs.  1,  Iff,  h.    Walcott,  1891:  Tenth  Ann.  Rept.  U.  S.  Geol. 

Surv.,  p.  608,  PI.  LX VII,  flgs.  5.  5a-e.    Hall  and  Clarke,  1892 :  Pal.  New  York, 

Vol.  VIII,  Pt.  I,  p.  102,  figs.  55-57.     ( "?)  Matthew,  1895 :  Trans.  New  York  Acad. 

Sci.,  Vol.  XIV,  p.  126. 

This  species  was  described  and  illustrated  by  me  in  Bulletin  No.  30, 
Monograph  VII,  and  the  Tenth  Annual  Report,  of  the  United  States  Geo- 
logical Survey.  It  occurs  with  both  the  Middle  and  the  Upper  Cambrian 
faunas  in  the  Park. 

Formation  and  locality:  Middle  Cambrian,  Flathead  terrane,  ranging 

from  the  lowest  terrane;  Gallatin  ten-ane,  upper  beds;  Crowfoot  section, 

Gallatin  Range ;  spur  at  southeast  head  of  first  branch  from  head  of  Gallatin 

Valley,  south  side;  Yellowstone  National  Park. 

-29 


450  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

BILLINGSELLA  Hall. 

Billvu/sella  Hall  aud  Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I.  p.  230,  PI.  VII 
A,  figs.  1-9. 

BiLLINGSELLA    COLORADOENSIS    SllUUiai'd. 

PL  LXI,  figs  1,  la-d. 

Orthis  coloradoensis  Shumard,  1860:  Trans.  St.  Louis  Acad.  Sci.,  Vol.  I,  p.  627. 

Orthis  pepina  Hall,  1863 :  Sixteenth  Ann.  Kept.  New  York  State  Cab.  Nat.  Hist., 
p.  134,  PI.  VI,  figs.  23-27.  Hall,  1867 :  Trans.  Albany  Institute,  Vol.  V,  p.  113. 
Whitfield,  1882:  Geol.  Wisconsin,  Vol.  IV,  p.  170,  PI.  I,  figs.  4,  5. 

Orthis  f  {Orthisina?)  pepina  Hall,  1883:  Second  Ann.  Eept.  New  York  State  Geol- 
ogist, PI.  XXXVII,  tigs.  16-19. 

Billingseaa  pepina  Hall  aud  Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  p.  230,  PI. 
VII,  figs.  16-19;  PI.  VIIA,  figs.  7-9. 

This  species  was  described  by  Shumard,  in  1860,  as  from  the  Potsdam 
sandstone  of  the  IS!  ew  York  series,  near  the  head  of  Morg-ans  Creek,  Burnett 
County,  Texas.  He  states  that  "tlie  general  form  of  the  shell  is  very 
similar  to  a  species  in  my  cabinet  from  the  Potsdam  sandstone  of 
Minnesota." 

In  1863  Professor  Hall  described  a  similar  shell,  from  the  sandstone 
al)ove  Lake  Pepin,  Minitesota,  under  the  name  of  Orthis  pepina,  stating  that 
when  compared  with  Orthis  coloradoensis  from  Texas  the  species  is  much 
smaller,  the  length  of  the  ventral  valve  is  greater,  and  the  strife  are  finer. 
However,  a  comparison  of  an  extended  series  of  specimens  collected  in  the 
Upper  Cambrian  of  Burnett  County,  Texas,  leads  me  to  believe  that  the 
specimens  from  widely  separated  locaUties  all  belong  to  the  one  species 
BillingseUa  coloradoensis. 

The  size  and  form  of  these  species  appear  to  be  remarkably  constant 
wherever  found,  as  is  also  the  surface  ornamentation,  which  consists  of  fine 
concentric  stria?  and  slender  radiating  costte,  which  are  often  unequal  in 
size.  The  concentric  striae  are  unusually  well  shown  in  the  material  from 
Texas,  while  the  radiating  costaj  are  ver)'  faint.  On  specimens  from  the 
St.  Croix  sandstone  of  Lake  Pepin,  Minnesota,  the  costse  and  the  concentric 
striae  and  lines  of  growth  are  strong  and  well  shown  in  the  casts  of  the 
outer  surface  of  the  shell.  The  generic  characters  are  finely  shown  by 
specimens  from  the  Gallatin  Range  in  the  Park,  in  which  the  charactei-istic 
muscular  scars  of  the  ventral  valve  of  BillingseUa  are  well  preserved;  also 


CAiMUKIAX  FOSSILS.  45^ 

the  high,  nearly  vertical  area,  and   the   large  delthyrimn,  partially  closed 
by  a  convex  deltidiuni. 

Formation  an.l  locality:   Upper  Cambrian,  Gallatin  terrane,  Crowfoot 
section,  (Jallatm  Kange ;  also  on  the  north  slope  of  the  Crowfoot  Rid-e 
on  the  south  side  of  the  Gallatin  Valley,  and  on  the  divide  between  Panther 
Creek  and  the  Gallatin  Kiver. 

ORTHIS  Dalman. 

Okthis  (?)  REMNicHA  Winchell. 

PI.  LXI,  ligs.3,  3a;  PI.  LXII,  figs.  1,  la-d 

Ortlns  remnicha  WiucheU,lSSG:  Fourteeuth  Anu.  Eept.  Geol.  and  Nat.  Hist.  Surv 
Mmuesota,  p.  317,  PI.  II,  flg.  7 . 

Shell  of  medium  size,  usually  slightly  transverse,  with  an  oblong,  oval 
outhne  tor  the  ventral  valve,  and  a  subquadrate  to  semicircular  outHne  for  the 
dorsal  valve.  Valves  moderately  convex,  with  an  almost  straight  hino-e  line 
that  vanes  in  length  from  nearly  the  greatest  width  of  the  shell  to  two- 
thuds  the  greatest  width;  cardinal  angles  varying  from  90°  or  less  in  the 
extreme  forms,  with  ears  somewhat  angular,  to  the  other  extreme,  where 
they  are  very  obtuse  and  have  the  appearance  of  being  almost  rounded 
their  angle  being  not  less  than  120°.  Cardinal  area  narrow  but  well  devel- 
oped on  each  valve,  and  divided  by  a  rather  large  delthyrium. 

The  ventral  (pedicle)  valve  has  in  some  specimens  a  shallow  mesial 
depression,  and  in  some  examples  it  is  slightly  flattened  toward  the  cardinal 
angles;  beak  small  and  curving  down  toward  the  hinge  line,  beyond  which 
It  projects  slightly.  Dorsal  (brachial)  valve  slightly  less  convex  than  the 
ventral.  Beak  small,  scarcely  projecting  beyond  the  hinge  line 
_  Surface  marked  by  bifurcating,  radiating  cost^,  that  vary  on  shells  of 
similai-  size  from  16  in  the  space  of  5  mm.  to  3  in  the  same  space  This 
variation  is  shown  in  the  specimens  from  the  Park,  as  well  as  in  those  from 
lexas  and  Wisconsin.  In  well-preserved  specimens  very  fine,  radiatino- 
raised  stri^  occur  both  on  the  costae  and  on  the  intervening  depressiont. 

W-'r  Tw-"""  ~'  '^'"  '"'*'  "^  '^''  ^^^^"^  ^^-^^'^  *1^^  S*-  C^-oix  sandstone  of 
Wmhe  d,  Wisc.->nsin,  and  on  the  larger  shells  from  the  limestones  of  the 
upper  Middle  Cambrian  horizon  of  Texas  and  the  Park 

The  interior  of  the  ventral  (pedicle)  valve  shows  a  slightly  raised, 


452     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

rather  small  muscular  area,  and  the  interior  of  the  dorsal  (brachial)  valve 
a  slightly  elevated  area  upon  which  occurs  a  naiTOw,  short  median  septum. 
The  crural  plates  are  also  well  shown.  In  casts  of  the  interior  from  the 
St.  Croix  sandstone  of  Wisconsin  the  dental  lamellae  of  the  ventral  valve 
are  finely  shown,  and  in  the  dorsal  valve  the  median  septum  and  crural 
plates. 

This  is  one  of  the  most  variable  shells  that  occur  in  the  Cambrian 
fauna.  Its  range  of  variation  is  such  in  all  of  the  widely  separated  locali- 
ties in  which  it  occurs  that  one  would  scarcely  hesitate,  if  in  possession 
only  of  the  extremes,  to  identify  two  well-marked  species.  The  variation 
is  not  only  in  the  radiating  cost?e,  but  also  in  the  general  form  of  the  shell. 
It  is  proposed  to  illusti'ate  this  variation  somewhat  fully  in  a  memoir  on 
the  Brachiopoda  of  the  Cambrian  fauna. 

Formation  and  locality :  Near  base  of  Upper  Cambrian,  Gallatin  ter- 
raue,  Crowfoot  section,  Gallatin  Range,  Yellowstone  National  Park.  It 
also  occurs  at  a  slightly  lower  horizon  on  the  south  side  of  the  Gallatin 
Valley,  and  specimens  were  collected  farther  to  the  north  by  Dr.  A.  C. 
Peale,  opposite  the  mouth  of  Pass  Creek,  in  the  Gallatin  Valley,  Montana. 

Orthis  (?)  SANDBERGi  Winchell. 

PI.  LXI,  figs.  2,  2a-d. 

Orthis  sandbergi  Winchell,  1886 :  Fourteenth  Ann.  Kept.  GeoL  and  Nat.  Hist.  Surv. 
Minnesota,  p.  318,  PI.  II,  figs.  8,  9. 

Shell  small,  transverse,  subquadrate  in  outline,  exclusive  of  the  acute 
angular  ears.  Valves  slightly  convex,  with  a  straight  hinge  line  longer 
than  the  greatest  width  of  the  shell ;  cardinal  area  naiTOw  l3ut  well  devel- 
oped on  each  valve  and  divided  by  a  rather  large  open  delthyrium. 

The  ventral  (pedicle)  valve  slightly  flattened  at  the  ears,  rising  toward 
the  center  with  a  convex  triangular  swelling,  broadening  from  the  narrow 
beak  to  the  front ;  beak  small,  rounded,  and  extending  slightly  beyond  the 
hinffe  line.  Dorsal  valve  flattened  at  the  ears,  with  well-marked  rounded 
ridges  rising  between  the  ears,  and  a  rather  broad,  well-detined  median 
sinus ;  beak  very  small,  slightly  encroaching  upon  the  hinge  line. 

Surface  marked  by  fine,  regular,  radiating  strife,  between  which  one  or 
more  faint  intermediate  strife  are  sometimes  visible;  under  favorable  con- 


OAMBIilAN  FOSSILS.  453 

ditious  very  fine  concentric  stria;  can  ])e  seen,  and  there  are  also  usually 
present  more  or  less  distinctly  marked  lines  of  growth. 

The  generic  cliaracter  of  this  species  has  not  been  fully  ascertained, 
but  the  material  from  the  Park  and  specimens  from  the  typical  locality 
at  Red  Wing,  Minnesota,  lead  me  to  think  that  this  can  not  l^e  referred  to 
the  genus  Billingsella.  It  appears  to  be  an  Orthis  of  the  Plectorthis  group 
of  Hall  and  Clarke. 

A  comparison  with  specimens  of  Orthis  sandhergi  from  the  typical 
locality  at  Red  Wing,  Minnesota,  shows  the  two  shells  to  be  specifically 
identical,  as  far  as  the  comparison  of  casts  in  sandstone  can  be  made  with 
well-jireserved  shells  on  the  surface  of  a  limestone  slab.  This  is  the  only 
species  of  the  type  known  to  me  in  the  Cambrian  fauna.  It  is  a  type  that 
is  developed  in  the  Ordovician  fauna,  and  I  think  it  will  be  found  to  occur 
in  the  Calciferous-Chazy  fauna  of  New  York  and  the  St.  Lawrence  Valley. 

Formation  and  locality:  Upper  Cambrian,  north  side  of  Elk  Pass, 
between  Buffalo  and  Slough  creeks,  Yellowstone  National  Park. 

PLATYCERAS  Conrad. 

Platyceras  primordialis  Hallf 

PI.  LXIII,  fig.  1. 

Platyceras  primordialis  Hall,  1863,  Sixteenth  Aim.  Kept.  New  York  State  Cab  Nat 
Hist.,  p.  136,  PL  YI,  fig.  28. 

^  A  single  species  of  Platyceras  occurs  on  a  slab  of  limestone  in  asso- 
ciation with  BiUingsella  pepina,  Ptyclioparia  (L.)  wisconsensis,  and  Ptijcho- 
paria  (1)  diadematus. 

So  far  as  can  be  determined  from  a  comparison  of  the  single  specimen, 
it  is  probable  that  the  forms  are  identical. 

Formation  and  locality:  Middle  Cambrian,  Gallatin  terrane,  north  side 
of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  Creek  and 
Soda  Butte  Creek,  Yellowstone  National  Park. 


454  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

HYOLITHES  Eichwald. 

Hyolithes  primordialis  Hall. 

PI.  LXIII,  figs.  2,  2a. 

Theca  primordialis  Hall,  1861 :  Aun.  Eept.  Progress  Geol.  Surv.  Wiscousin,  p.  48. 

Hall,  1862:  (ieol.  Kept.  Wisconsin,  Vol.  I,  p.  21,  fig.  5.     Hall,  1863:  Sixteenth 

Ann.  Eept.  New  York  State  Cab.  Nat.  Hist.,  p.  135*,  PI.  VI,  figs.  30, 31. 
Pugiunciilus  primordialis  Hall,  1863:  Ibid.,  p.  135*. 
Theca  (Ptigiunculus)  gregaria  M.  and  H.,  1861:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  2d 

series,  Vol.  Y,  p,  436.    M.  and  H.,  1864 :  Pal.  Upper  Missouri,  Pt.  I,  p.  5. 
HyolitheS  {Theca)  primordialis  Hall  and  Whitfield,  ]873:   Twenty-third  Ann.  Eept, 

New  York  State  Cab.  Nat.  Hist.,  p.  242,  PL  II,  fig.  3. 
Hyolithes  primordialis  f  White,  1874:   Expl.  Surv.  West  100th  Merid.,  Prelim.  Eept., 

Invert.  Foss.,  p.  6. 
Hyolithes  primordialis  White,  1875:  Ibid.,  Final  Eept.,  Vol.  IV,  Pt.  I,  p.  37,  PI.  I,  figs, 

5rt-e.     Whitfield,  1883 :  Geol.  Wisconsin,  Vol.  IV,  p.  175,  PL  I,  fig.  12.    Walcott, 

1884 :  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  Pal.  Eureka  District,  pp.  23, 24, 

Forms  of  this  species  occur  at  several  localities,  and  are  identical  with 
those  found  in  the  Middle  Cambrian  St.  Croix  sandstone  of  Wisconsin. 
They  vary  in  length  from  1  to  5  cm.  The  young  individuals  when  grouped 
together  in  the  limestone  are  very  closely  related  to,  if  not  identical  with, 
Theca  grefiaria}  The  type  specimens  of  the  latter  were  found  near  the 
head  of  Powder  River  in  the  Bighorn  Mountains  of  Idaho  Territory,  now 
in  Wyoming. 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation.  Crow- 
foot section,  Gallatin  Range;  Clark  Fork  Valley,  south  side,  between 
Lodge  Pole  and  Reef  creeks;  and  blufiF  on  south  side  of  Pebble  Creek, 
north  of  saddle  to  Soda  Butte  Creek,  Yellowstone  National  Park. 

AGNOSTUS  Brongniart. 

Agnostus  interstrictus  White. 
PL  LXIII,  figs.  3,  3fl. 
Agnostus  interstrictus  White,  1874:  Geol.  and  Geog.  Expl,  West  100th  Merid.,  Prelim, 
Eept.,  Invert.  Foss.,  p.  7.     White,  1S75:  Ibid.,  Final  Eept.,  Vol.  IV,  Pt.  I, 
p.  38,  PL  II,  5a,  h.    Walcott,  1886:  Bull.  U.  S.  Geol.  Surv.  No.  30,  p.  149,  PL 
XVI,  figs.  6,  6o. 

A  comparison  of  the  specimens  from  the  Gallatin  Range  with  the  type 
specimens  from  the  Springhouse  Range  of  Utah  leads  to  the  conclusion 


'  PaL  Upper  Missouri,  Pt.  I,  1864,  p.  5. 


CAMBRIAN  FOSSILS.  455 

that  they  represent  the  siuiie  species.  Tliere  are  no  good  specimens  of  the 
head,  but  tliere  is  one  very  well  preserved  pygidiiini.  This  and  the  type 
specimen  are  illustrated. 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation.  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 

Agnostus  bidens,  Meek. 
PI.  LXIII,  figs.  4,  ia. 

Agnostus  bidens  Meek,  1873:  Sixth  Aim.  Kept.  U.  S.  Geol.  aud  Geog.  Surv.  Terr.,  for 
1872,  p.  46.3.  Walcott,  1884:  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  26,  PI.  IX, 
figs.  13,  13rt. 

The  specimens  representing  this  species  include  the  head  and  pygidium 
only.  There  is  considerable  similarity  between  this  species  and  A.  inter- 
str ictus  and  A.  josephus,  the  latter  from  the  St.  Croix  sandstone  of  Wisconsin. 
They  all  belong  to  the  Middle  Cambrian  fauna,  and  it  will  be  only  after  a 
careful  examination  with  an  extended  series  of  specimens  that  the  speciiic 
characters  are  well  determined. 

The  originals  of  the  type  specimens  were  found  on  the  east  side  of 
the  Gallatin  River,  above  the  town  of  Gallatin,  they  being  associated  with 
essentially  the  same  fauna  as  that  with  which  they  occm-  in  the  Gallatin 
Range. 

Formation  and. locality:  Middle  Cambrian,  Flathead  formation.  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 

Agnostus  tumidosus  Hall  and  Whitfield. 

PI.  LXIII,  figs.  5,  5rt. 

Agnostus  tumidosus  Hall  aud  Whitfield,  1877;  U.  S.  Geol.  Expl.  40th  Par.,  Pt.  II, 
p.  231,  PI.  I,  tig.  32. 

This  species  is  represented  by  a  small  cephalic  shield,  and  there  is  an 
associated  pygidium  that  is  referred  to  it.  The  species  was  founded  upon  a 
small  head  discovered  in  the  Eureka  district  of  Nevada.  It  is  a  strongly 
marked  species  and  not  liable  to  be  confused  with  any  other  species  of  the 
genus  from  the  Cambrian  rocks  of  the  Rocky  Mountain  region. 

Formation  and  locality :  Middle  Cambrian,  Flathead  formation.  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 


456  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

PTYCHOPARIA  Corda. 

Ptychoparia  penfieldi  u.  sp. 

PI.  LXV,  tigs.  4,  4a,  b. 

Of  this  species  there  are  in  the  collection  the  central  parts  of  the  head, 
the  interior  of  one  free  cheek,  and  one  pygidium.  The  general  form  of  the 
head  is  trausvei'se,  semicircular;  the  frontal  rim  strong,  rounded,  and 
separated  from  the  frontal  limb  and  free  cheeks  b}^  a  well-defined  rounded 
furrow;  postei'ior  lateral  angles  prolonged  into  slender  spines.  Glabella 
truncato-conical ;  nearly  as  broad  at  the  base  as  long;  marked  by  three 
pairs  of  glabella  furrows,  which  penetrate  about  one-fourth  the  distance 
across ;  the  posterior  pair  bend  slightly  backward  and  penetrate  toward  the 
center.  Fixed  cheeks  narrow  and  separated  from  the  glabella  by  a  well- 
defined  dorsal  furrow,  from  the  narrow  posterior  rim  by  a  rather  broad, 
clearly  defined  furrow ;  anteriorly  they  merge  into  the  rather  narrow 
frontal  limb.  Palpebral  lobes  narrow  and  clearlj'-  defined  by  a  groove  from 
the  fixed  cheek;  they  are  nearly  one-tliird  the  length  of  the  cheek;  ocular 
ridges  barely  discernible  above  the  general  surface  of  the  cheek.  The 
posterior  lateral  lobe  of  the  fixed  cheek  extends  outward,  so  as  to  give  a 
total  length  from  the  glabella  outward  somewhat  greater  than  the  width  of 
the  glabella  at  the  base.  The  associated  free  cheek  has  a  strong  marginal 
rim  and  well-marked  furrow  between  it  and  the  main  body  of  the  cheek, 
which  reaches  up  to  the  palpebral  lobe. 

Pygidium  small,  semicircular;  axial  lobe  strongly  defined  and  marked 
by  three  segments  and  a  short  terminal  portion;  lateral  lobes  marked  by 
thi-ee  rather  broad  segments  that  merge  into  the  smooth  outer  rim.  Surface 
apparently  smooth. 

Formation  and  locality:  Middle  Cambrian,  Flathead  terrane,  Crow- 
foot section,  Grallatin  Range,  Yellowstone  National  Park. 

Ptychoparia  antiquata  Salter  sp. 
PI.  LXV,  figs.  7,  la. 
Conocejphalus  antiquatus :  Quart.  Jour.  Geol.  Soc.  London,  Vol.  XV,  p.  554,  tig.  2. 

This  species  was  founded  on  an  entire  trilobite  sent  to  the  great  exposi- 
tion in  London  in  1851.     It  was  said  to  have  been  discovered  somewhere 


OAMBIIIAN  FOSSILS.  457 

in  the  State  of  Georgia.  From  the  occurrence  of  laro-e  numbers  of  entire 
specimens  on  nodules  in  the  Coosa  VaHey,  in  Alal)ama,  a  few  miles  west  of 
the  Georg-ia  State  line,  it  is  thought  pnjbaljle  that  the  specimen  referred  to 
came  from  that  locality.  A  comparison  of  a  series  of  specimens  from  the 
Coosa  Valley  locality  with  the  Gallatin  Range  specimens  shows  a  very 
close  resemblance  between  them.  The  Alabama  specimens  have  two 
marked  ^-ariations  in  the  frontal  limb  and  border;  in  one  the  limb  is  gently 
rounded  to  a  marked  groove  that  separates  it  from  a  strong  rounded  frontal 
rim;  in  the  other,  the  groove  in  the  frontal  rim  curves  backward  from  each 
side  toward  the  glal^ella  so  as  to  indent  the  frontal  limb.  As  a  result  of  the 
comparison,  it  is  found  that  the  range  of  variation  among  the  individuals  ol 
P.  antiquata  includes  not  only  the  Gallatin  species  but  also  the  varieties  of  it. 
Formation  and  locality:  Middle  Cambrian,  Flathead  formation.  Crow- 
foot section,  Gallatin  Range;  bluff  on  south  side  of  Pebble  Creek,  north  of 
saddle  to  Soda  Butte  Creek;  on  ridge  near  Crowfoot  section,  Gallatin 
Range,  Yellowstone  National  Park.  East  of  Dead  Indian  Creek,  Absaroka 
Range,  Wyoming. 

Ptychoparia  (E.)  afpinis  Walcott. 

PI.  LXV,  fig.  8. 

Ptychoparia  (E.)  affinis   Walcott,   1884:    Mou.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  54,  PI. 
X,  fig.  12. 

With  the  material  at  hand  it  is  impossible  to  make  a  positive  identifi- 
cation Avith  the  type  species  from  the  Upper  Cambrian  of  the  Eureka 
district,  Nevada.  There  is,  however,  a  striking  similarity  in  the  only  por- 
tions we  have  for  comparison,  the  center  of  the  head. 

A  similar  species  occurs  in  the  Cambrian  beds  of  Honey  Creek,  Bur- 
nett County,  Texas,  and  it  is  probable  that  the  specimens  from  the  three 
widely  separated  localities  are  identical. 

Formation  and  locality:  Middle  Cambrian,  Gallatin  limestone,  Liv- 
ingston section,  at  head  of  Davis  Creek,  Snowy  Range,  Montana. 


458  GEOLOG^Y  OF  THE  YELLOWSTONE  N ACTIONAL  PAKK. 

Ptychoparia  llanoensis  Walcott  (?) 

PI.  LXIV,  fig.  4. 

Ptychoparia  llanoensis  Walcott,  1890:    Proc.  U.  S.  Nat.  Miis.,  Vol.  XHl,  p.  272,  PL 
XXI,  flgs.  3-5. 

The  fragments  that  have  been  compared  and  provisionally  identified 
with  this  species  show  only  the  central  portions  of  the  head.  The  frontal 
rim  and  border,  separated  by  a  narrow,  raised,  crenulated  line  on  the  cast 
of  the  under  surface  of  the  test,  and  the  glabella,  appear  to  be  identical  with 
those  of  some  of  the  specimens  of  P.  llanoensis. 

Formation  and  locality:  Middle  Cambrian,  Livingston  section,  at  head 
of  Davis  Creek,  Snowy  Range,  Montana. 

Ptychoparia  sp.  undet. 
PI.  LXIV,  fig.  5. 

This  is  a  rather  strongly  marked  form,  of  which  only  the  central  por- 
tion of  the  head  is  preserved.  It  differs  from  other  described  species  in 
having  the  frontal  rim  project  inwardly  almost  to  the  front  margin  of  the 
glabella.  A  figure  is  presented  of  the  onl}^  specimen  in  the  collection. 
The  head  may  be  compared  with  the  head  oi  Ptychoparia  teucer,  from  the 
red  sand  rock  of  Highgate  Springs,  Vermont.^  It  is  possible  that  this  is  a 
strongly  marked  variety  of  P.  anfiqnata. 

Formation  and  locality:  Middle  Cambrian,  Flathead  tVirmation,  near 
Crowfoot  section,  Grallatin  Range,  Yellowstone  National  Park. 

Ptychoparia  (?)  sp.  undet. 
PI.  LXIV,  fig.  3. 

This  is  a  clearly  marked  form,  represented  by  the  central  portion  of 
the  head.  The  small  eye  lobes  and  strong  postero-lateral  limbs  suggest 
Ptychoparia  eryon  Hall,"  but  the  glabella  is  less  elongate  and  the  frontal  limb 
is  marked  by  a  rounded  rim. 

Formation  and  locality:  Middle  Cambrian,  Crowfoot  section,  Gallatin 
Range,  Yellowstone  National  Park. 

•  Tenth  Ann.  Kept.  U.  S.  Geol.  Siirv.,  1891,  PI.  XCVI,  fig.  3. 

2  Sixteenth  Ann.  Rept.  New  York  State  Cub.  Xat.  Hist.,  1863,  PI.  VIII,  Hgs.  16,  31. 


CAMBRIAN  FOSSILS.  459 

CRE  PICE PH ALUS  Owen. 

Crepivephalm  Owen,  1852:  Kept.  Geol.  Siirv.  Wisconsin,  Iowa,  aud  Minnesota,  p.  57(1, 
PI.  I,  fig.  S;  PI.  lA,  tigs.  10, 1(5, 18.  Hall,  1803:  Sixteentli  Ann.  Rept.  New  York 
State  Mus.  Nat.  Hist.,  p.  147.  Hall  and  Whitfield,  1877 :  Rept.  Geol.  Expl.  40tli 
Par.,  Vol.  IV,  Pt.  11,  p.  209.  Whitfield,  1870:  Rept.  Reconnaissance  from  Car- 
roll, Montana,  to  Yellowstone  National  Park  (Ludlow),  p.  141.  Whitfield,  1880: 
Rept.  Geology  and  Resources  of  the  P>lack  Hills  (Jenuey),  p.  341.  Whitfield, 
1882:  Geol.  Wisconsin,  Vol.  IV,  p.  182.  Walcott,  1884:  Bull.  U.  S.  Geol.  Surv. 
No.  10,  p.  30.     Walcott,  1880 :  Bull.  U.  S.  Geol.  Surv.  No.  30,  pp.  206,  207. 

Attention  was  called  to  this  genus  in  1886,'  but  in  giving  an  entire 
figure  of  C.  texunus  I  will  repeat  the  description  given  by  Dr.  Owen,  and 
also  add  a  few  remarks. 

Dr.  Owen  projiosed  the  generic  name  Crepicephalus  for  some  fragmen- 
tary remains  of  trilobites,  the  characteristic  features  of  the  central  portion  of 
the  head  of  which  he  described,  and  he  also  gave  figures  of  the  associated 
pygidia.     The  description  of  the  central  portion  of  the  head  is  as  follows: 

The  rather  flat  slipper-shaped  glabella  is  tapering  and  slightly  acuminated 
anteriorly,  with  a  faint  ridge  in  the  median  line;  two  small  and  very  superficial 
depressions,  and  a  posterior  faint  furrow,  very  partially  divide  the  glabella.  The 
facial  sutures  run  nearly  parallel  to  the  margin  of  the  glabella,  and  join  a  thickened, 
cordlike,  anterior  narrow  border,  inclosing  a  convex  area,  narrower  in  front  than  at 
the  sides.  Oblique  plications  can  sometimes  be  traced  on  the  cheek  plate,  in  advance 
of  the  eye,  converging  toward  the  apex  of  the  glabella. 

In  his  remarks  on  the  genus,  he  refers  to  figs.  10,  16,  and  18  of  PI. 
Ia,  as  illustrating  the  central  portions  of  the  ceplialic  shield  of  the  genus. 
The  comparison  of  these  figures  with  typical  specimens  of  Crei)icephalus 
(Owen's  Dikellocephaliis)  iowensis  shows  clearly  that  the  types  of  the  genus 
Crepicephalus  should  have  been  referred  to  this  species.  He  also  refers  to 
the  associated  pygidia  which  are  illustrated  by  his  fig.  8  of  PI.  I  and  fig.  16 
of  PI.  Ia,  a  comparison  of  the  pygidium  of  Crepicephalus  iowensis  with  these 
figures  showing  it  to  be  identical. 

In  the  description  of  fig.  13  (PI.  I)  the  species  tvisconsinensis  is  referred 
with  a  (?)  to  the  genus  Crepicephalus.  No  reference,  however,  is  made  to  it 
in  the  text.  Professor  Hall,  in  referring  to  the  genus,^  speaks  of  this  as  the 
only  species  designated  by  Dr.  Owen,  and  states  that  it  off"ers  no  distinction,  in 
regard  to  the  head,  from  a  species  placed  under  the  genus  Lonchocephalus. 

'  Bull.  U.  S.  Geol.  Surv.  No.  30,  pp.  206,  207.  ^Loc.  cit.,  p.  147. 


460     GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

He  considered  it  difficult  to  sustain  this  genus,  or  either  of  them,  upon  the 
characters  given,  and  referred  all  to  the  genus  Conocephalites. 

Messrs.  Hall  and  Whitfield,  in  describing  Cambrian  trilobites  from 
Utah  and  Nevada,  discussed  the  genus  Conocephalites  and  revived  Crepi- 
cephalus  as  a  subgenus  equivalent  to  Loganellus  of  Devine.  They  did  not, 
however,  describe  the  genus  Crepicephalus,  but  refen-ed  a  number  of  species 
to  it  which  possess  more  or  less  distinctly  marked  "slipper-shaped"  glabellte. 
Professor  Whitfield  subsequently  used  the  genus  in  his  description  of 
Crepicepludus  (LoganellMs)  montanensis;^  also  in  the  Paleontology  of  the 
Black  Hills  of  Dakota."  But  later  (1882)  he  omitted  reference  to  Loganellus 
in  describing  Crepicephalus  onustus? 

In  1884  I  stated  that  Crepicephalus  might  be  used  as  a  subgenus  of 
Ptychoparia  on  account  of  its  peculiar  pygidium,  but,  from  a  recent  study  of 
an  entire  specimen  of  the  type  species  and  of  C.  fexanus,  I  think  that  we  can 
with  propriety  use  it  as  a  full  generic  term.  The  essential  elements  of  the 
head  are  genericall}^  identical  with  those  of  the  head  of  Ptychoparia  striata, 
but  the  pleura  of  the  thoracic  segments  and  the  pygidium  vary  in  a  marked 
manner.  The  pleura  terminates  in  the  graceful  backward-curving  acu- 
minate points  so  characteristic  of  many  species  of  Paradoxides.  This  may 
not  be  considered  a  character  of  generic  value,  but  it  gives  a  marked  aspect 
to  the  body  of  the  trilobite  in  both  C.  ioivensis  and  C.  texanus.  The  pygidium 
of  C.  iowensis  is  short,  broad,  and  provided  with  two  long  postero-lateral 
spines  which  appear  to  be  an  extension  of  the  border,  but  in  reality  are  the 
lateral  extension  of  one  of  the  segments  of  the  pygidium.  This  feature  is 
more  clearly  shown  in  the  pygidium  of  C.  texanus.  The  combination  of 
characters  in  the  head,  thorax,  and  pygidium  clearly  distinguishes  the 
genus  from  Ptychoparia  and  other  genera  of  the  Conocephalidae. 

Crepicephalus  texanus  Shumard  sp. 
PI.  LXV,  fig.  5. 

Arionellus  {Bathyurus)  te.ramis  Sliumard,  1861:  Am.  Jour.  Sci.  and  Arts,  2d  series. 

Vol.  XXXII,  p.  218. 
Arionellus  tripnnctatus  ^Yhit&eld,  1816:  Kept.  Reconnaissance  from  Carroll,  Montana 

Terr.,  on  the  Upper  Missouri,  to  the  I'ellowstone  National  Park  (Ludlow),  p.  141 

PL  I,  figs.  3-5. 

Numerous  heads  of  this  species  occur  in  a  dark-greenish-colored  oolitic 

'  Bull.  U.  S.  Geol.  Suiv.  No.  30,  p.  Ul.  ^'Loc.  cit.,  pp.  341-343.  sLoc.  cit.,  p.  182. 


CAMUlilAN  FOSSILS.  4GI 

limestone,  with  a  few  frao-ments  of  the  pygidium.  The  material  is  too  poor 
to  properly  illusti'ate  tlie  species,  and  a  tif>-ure  is  introduced  that  was  di-awn 
from  specimens  collected  in  the  Middle  Cambrian  shaly  beds  of  the  Coosa 
Valley,  Alabama.  A  detailed  desci'iption  of  the  species  and  full  illustrations 
will  be  given  in  a  memoir  on  the  Middle  and  Upper  Cambrian  faunas,  now 
being  jn-epared. 

The  type  specimens  of  the  species  were  described  by  Dr.  Shumard 
from  Llano  County,  Texas.  I  collected  a  series  of  specimens  from  the  type 
locality,  and  a  comparison  of  these  with  those  from  Moss  Agate  Springs, 
near  Cami)  Baker,  Montana  (described  as  Arionelliis  tripunctatus  by  Whit- 
field), and  the  Coosa  Valley,  Alabama,  shows  them  to  belong  to  one  species. 

Formation  and  locality :  Middle  Cambrian,  Flathead  terrane,  north 
side  of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  Creek 
and  Soda  Butte  Creek ;  Flathead  terrane,  Crowfoot  section,  Gallatin  Range, 
Yellowstone  National  Park. 

PTYCHOPAKL-i  (LoNCHOCEPHALUS)  HAMULUS  Owen! 

Lonehocephalus  lianmlus  Owen,  1852:  Geol.  Kept.  Wisconsiu,  Iowa,  and  Minnesota, 

p.  576,  PI.  lA,  figs.  8,  12. 
Conocephalites  hamulus  Hall,  1863:  Sixteenth  Ann.  Eept.  New  York  State  Mus.  Nat. 

Hist,,  p.  166,  PI.  VII,  figs.  43,  44;  PI.  VIII,  figs.  25,  26. 

One  imperfect  head  is  all  there  is  in  the  collection  on  which  to  base 
the  presence  of  this  species.  Little  more  can  be  said  than  that  there  is  a 
form  which  represents  it. 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation,  north 
side  of  Soda  Butte  Creek,  on  ridge  between  Pebble  Creek  and  Soda 
Butte  Creek,  Yellowstone  National  Park. 

Ptychoparia  (Lonchocephalus)  WISCON.SENSIS  Owen  sp. 
PI.  LXIV,  figs.  1,  la-c. 

Grepicephalus  ( 1)  loisconsensis  Owen,  1852 :  Eept.  Geol.  Surv.  Wisconsin,  Iowa,  and 

Minnesota,  description,  PI.  I,  fig.  13. 
Dicellocephalus  latifrons  Shumard,  1803:  Trans.  St.  Louis  Acad.,  Vol.  II,  p.  101. 
Conocephalites  loisconsensis  Hall,  1863:  Sixteenth  Ann.  Eept.  New  York  State  Cab. 

Nat.  Hist.,  p.  164,  PI.  VII,  figs.  39-41;  PI.  VIII,  figs.  22-24,  27,  28. 

This  species  occurs  in  abundance  in  thin-bedded  limestone  in  the 
northeastern  portion  of  the  Park.      It  is  associated  with  Ptychoparia  (f)  dia- 


462  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

demata,  an  association  which  also  occurs  in  the  Middle  Cambrian  St.  Croix 
sandstone  of  Wisconsin.  Numerous  heads  occur,  but  only  one  fragmentary 
pygidium  has  been  seen.  An  illustration  of  the  pygidium  is  taken  from  a 
specimen  found  in  the  St.  Croix  sandstone  4  miles  southeast  of  Lake  City, 
Minnesota. 

Formation  and  locality:  Middle  Cambrian,  Flathead  foi-mation,  north 
side  of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  and  Soda 
Butte  creeks,  Yellowstone  National  Park. 

PtYCHOPARIA  (?)  DIADEMATA  Hall  Sp. 
PI.  LXIV,  figs.  2,  2a-c. 

Conocephalites  diadematus  Hall,  1863:  Sixteenth  Ann.  Kept.  New  Y^ork  State  Cab. 
Nat.  Hist.,  p.  107,  PI.  VII,  figs.  36-38;  PI.  VIII,  figs  18,  21. 

This  species  is  associated  with  Ptychoparia  (L.)  tvisconsensis.  The  cen- 
tral portions  of  the  head  are  quite  abundant  and  associated  with  the  sepa- 
rated free  cheeks.  Two  finely  preser^-ed  hypostomas  and  one  imperfect 
pygidium  also  occur  on  the  slabs  of  limestone.  The  pygidium  is  illustrated 
by  a  specimen  from  the  St.  Croix  sandstone,  found  in  the  bluff  near  Hudson, 
Wisconsin. 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation,  north 
side  of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  and  Soda 
Butte  creeks,  Yellowstone  National  Park. 

ARIONELLUS  Barrand. 

AriONELLUS   LEVIS  u.  sp. 
PI.  LXV,  fig.  1. 

It  is  with  little  doubt  that  the  specimen  illustrated  is  referred  to  this 
genus.  It  has  a  strougl)^  convex,  minute  head,  4  mm.  in  length;  glabella 
nearly  as  Ijroad  as  long,  narrowing  slightly  toward  the  broadly  rounded 
front;  glabella  furrows  barely  visible  as  four  shoi't,  slightly  depressed  lines. 
It  is  separated  from  the  fixed  cheeks  and  frontal  limb  by  a  narrow  groove, 
which  is  all  that  breaks  the  general  convexity  from  the  frontal  margin  back 
to  the  occipital  furrow.  The  occipital  furrow  is  deepl}'  impressed  between 
the  glabella  and  the  very  narrow  depressed  occipital  ring.  Fixed  cheeks 
slightly  convex,  sloping  abruptly  toward  the  facial  sutures;  anteriorly  they 


CAMBRIAN  FOSSILS.  463 

pass  into  the  rather  l)roa(l  tVoiit;i1  hiiil),  which  shipcs  directly  downward  to 
the  frontal  niaryin,  without  any  frontal  groove  or  rim.  The  palpebral  lobes 
are  situated  oj)posite  a  point  about  two-thirds  the  distance  from  the  jjos- 
terior  to  the  anterior  mar<>'in  of  the  glabella. 

Formation  and  locality:  Middle  Cambrian,  Gallatin  limestone,  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 

Arionellts  sp.  undet. 
PI.  LXV,  fig.  2. 

Only  the  central  portion  of  the  head  of  this  species  is  known.  It  is  so 
distinct  a  type  that  I  do  not  hesitate  to  refer  it  to  the  genus  Arionellus.  The 
glabella  is  elongate,  subcorneal;  the  glabella  furrows  are  indicated  by  very 
slight  depressions,  and  the  occipital  furrow  is  almost  obliterated.  Fixed 
cheeks  as  broad  as  the  glabella  and  merging  into  the  broad,  rounded, 
anterior  frontal  limb.  The  palpebral  lobes  are  broken  away  and  there 
does  not  appear  to  be  any  frontal  rim,  the  gently  rounded  slope  from  the 
glabella  to  the  margin  being  unbroken.  The  specimen  strongly  recalls 
specimens  of  Arionellus  from  the  Paradoxides  zone  of  Newfoundland. 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation,  north 
side  of  Soda  Butte  Creek,  below  saddle  on  ridge  between  Pebble  and  Soda 
Butte  creeks,  Yellowstone  National  Park. 

LIOSTRACUS  Angelin. 

LlOSTRACU.S    PARVUS  U.  Sp. 
Pi.  LXV,  fig.  6. 

This  form  is  I'epresented  by  the  central  portions  of  three  small  heads. 
The  glabella  is  a  little  longer  than  broad;  sides  subparallel,  broadly 
truncated  in  front;  three  pairs  of  small  glabella  furrows  are  slightly  indi- 
cated ;  occipital  furrow  narrow  and  slightly  impressed ;  occipital  ring  narrow 
at  the  sides,  broader  at  the  center,  and  provided  with  a  short  occipital  spine. 
Free  cheeks  broad,  convex,  and  separated  from  the  glabella  by  a  well- 
defined  dorsal  furrow;  anteriorl)^  they  merge  into  the  narrow  frontal  rim; 
ocular  ridges  narrow,  passing  almost  directly  outward  from  a  point  opposite 
the  anterior  pair  of  glabella  furrows  to  the  anterior  end  of  the  small, 
narrow  palpebral  lobe;  anterior  rim  nearly  flat  and  distinguished  from  the 


464  GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

frontal  lobe  by  its  smoothness  and  by  being  nearly  flat ;  posterior  lateral 
limb  of  fixed  cheeks  strong  and  extending  obliquely  outward  and  backward 
from  the  base  of  the  palpebral  lobe;  posterior  rim  narrow. 

Surface  slightly  granular  under  strong  magnifying  power. 

Formation  and  locality:  Middle  Cambrian,  in  bluff  south  side  of 
Pebble  Creek,  north  of  saddle  to  Soda  Butte  Creek,  Yellowstone  National 
Park. 

SOLENOPLEURA  Angelin. 

SOLENOPLEURA  ?   WEEDI. 
PL  LXV-,  figs.  9,  9a. 

Of  this  species,  only  the  central  portions  of  the  head  occur  in  the  col- 
lection. The  entire  individual  attained  considerable  size,  as  the  laro-est 
head  has  a  length  of  20  mm.  The  characteristic  features  of  the  head  are 
also  shown  in  heads  9  mm.  in  length. 

The  glabella  is  obtusely  conical,  having  a  width  at  the  base  in  the 
largest  specimen  of  10  mm.,  and  a  length  from  the  center  of  the  occipital 
furrow  to  the  frontal  limb  of  13  mm.  It  is  separated  from  the  strong 
rounded  occipital  ring  by  a  relatively  broad,  well-defined  furrow.  The 
posterior  pair  of  glabella  furrows  is  indistinctly  shown  by  very  shallow 
grooves  in  the  case  of  the  largest  individuals;  on  the  smaller  individuals  it 
is  not  shown,  except  by  a  smooth  spot.  The  glabella  is  separated  from  the 
fixed  cheeks  and  frontal  limb  by  a  well-marked  dorsal  furrow,  and  as  it  is 
quite  convex  it  stands  out  in  clear  relief  from  the  general  surface  of  the 
head.  Frontal  limb  short,  1.5  mm.  in  length  in  the  large  specimen.  It  is 
separated  from  the  strong  rounded  frontal  rim  by  a  well-defined  groove; 
laterally  it  passes  into  the  free  cheek,  which  is  of  medium  width.  The  pal- 
pebral lobe  is  of  medium  size  and  situated  at  a  point  opposite  the  transverse 
central  line  of  the  glabella.  A  faintly  defined  occular  ridge  extends  abruptly 
backward  across  the  fixed  cheek  from  a  point  a  little  back  of  the  front  of 
the  glabella  to  the  front  angle  of  the  palpebral  lobe.  It  is  defined  more 
by  the  presence  of  a  slight  groove  in  front  of  it  than  by  the  elevation  of  the 
ridge  itself.  The  posterior  lateral  limb  of  the  fixed  cheek  extends  outward 
two-thirds  of  the  width  of  the  glabella  at  the  base ;  it  is  separated  from  the 
posterior  rim  by  a  well-defined  furrow. 


CAMBRIAN  FOSSILS.  465 

Fragnit'iits  of  tin-  free  cheeks  associated  willi  the  glal)ella  slmw  tliat 
they  are  convex  and  tliat  the  strong  rounded  rim  is  sejjarated  from  the 
cheek  |)roi)er  l)y  a  well-marked  groove. 

The  entire  surface  of  the  head,  with  the  exception  of  the  occijiital 
groove  and  the  groove  within  the  outer  rim,  is  strongly  pustulose,  the 
pustules  being  scattered  irregularly  over  the  surface.  Where  the  true  test 
is  broken  awa}'  the  jjustules  are  shown  on  the  surface  of  the  cast. 

This  species  resembles  Bathyurus  coniciis  Billings,  from  the  Calciferous 
formation  of  northeastern  New  York  and  St.  Timothy,  Canada.  It  differs, 
however,  in  the  strongl}-  marked  frontal  rim  and  the  form  of  the  glabella.^ 
It  may  be  also  compared  with  Hall  and  Whitfield's  Crepicephalus  (L.) 
macuJosm} 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation,  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 

ZACONTHOIDES  Walcott. 

Zaconthoides  sp.  undet. 

PI.  LXV,  fig.  3. 

Head  moderately  convex ;  glabella  convex,  subclavate,  narrowino- 
very  slightly  from  the  anterior  toward  the  posterior  end;  marked  by  three 
pairs  of  slightly  impressed  glabella  furrows,  the  posterior  pair  cutting  in 
obliquely  backward  toward  the  occipital  fuiTOw.  Occipital  furrow  narrow 
but  distinctly  impressed;  occipital  ring  strong  and  provided  with  a  short 
strong  spine,  which  projects  from  the  upper  posterior  margin;  fixed  cheeks 
narrow  anteriorly  and  a  little  less  than  half  the  width  of  the  o-labella 
opposite  the  posterior  margin  of  the  palpebral  lobe;  anteriorly  they  pass 
down  to  the  frontal  rim,  there  being  practically  no  frontal  limb,  the  glabella 
extending  directly  down  to  the  margin  The  palpebral  lobe  is  nearly 
half  the  length  of  the  glabella;  anteriorly  it  extends  to  a  point  opposite  the 
anterior  glabella  furrow  and  posteriorly  to  a  point  opposite  the  occipital 
furrow. 

The  largest  specimen  of  this  species  is  3  mm.  iu  length;  a  second,  a 
smaller  one,  occurs  on  the  same  piece  of  limestone.     It  is  possible  tliat  thev 

'  Geol.  Surv.  Canada,  Pal.  Fossils,  Vol.  I,  1865,  p.  353,  tig.  3416. 
=  U.  S.  Geol.  Expl.  Fortieth  Par.,  Vol.  IV,  1877,  j).  215,  PI.  II,  tig.  24. 
MON   XXXIl,  PT   II 30 


466  GEOLOGY  OF  THE  YELLOWSTO^^E  NATIONAL  PARK. 

represent  the  young  of  Z.  spinosus}     The  head  diflPers  in  details,  but  not 
more  so  than  between  the  young-  and  adults  of  Z.  typicalis} 

Formation  and  locality:  Middle  Cambrian,  Flathead  formation,  Crow- 
foot section,  Gallatin  Range,  Yellowstone  National  Park. 

BATHYURISCUS  Meek! 

PI.  LXIV,  flg.  6. 

A  single  specimen  of  the  pygidium  is  placed  provisionally  under  this 
genus.  Its  principal  characters  are  well  shown  in  the  figure.  It  is 
associated  with  HyoUthes  primordialis,  and  is  probably  from  the  Middle 
Cambrian  liorizon.  The  genus  Dolichometopus  Angelin  might  include  this 
form,  but  with  the  material  at  hand  it  is  difficult  to  make  any  detailed 
comparison  of  generic  characters. 

Formation  and  locality :  Middle  Cambrian,  Flathead  formation,  east  of 
Dead  Indian  Creek,  Absaroka  Range,  Wyoming. 


'  Bull.  U.  S.  Geol.  Survey  No.  30,  p.  184,  PI.  XXV,  fig.  6.  '^  Loc.  cit.,  PI.  XXV,  flg.  2,  2a. 


PLATE   LX. 


467 


PLATE    LX. 

Page. 
Fig.  1.  Obohis  (Linf/iilepis)  aciiminatiis  var.  meeki 444 

1.  Ventral  valve,    x  3. 
1((.  Dorsal  valve,     x  3. 

Fig.  2.  Obohis  ( LhifiuleJla)  desideratus 445 

2.  Ventral  valve,     s  6. 
'2a.  Dorsal  valve,     x  6. 

Fig.  3.  Dicellomiis  uana 447 

3.  Ventral  valve,  from  Gallatin  Range,    x  6. 

3a.  Dorsal  valve,  from  Little  Rocky  Mountains,  Montana,     x  6. 

3h.  Ventral  val\e  (type  specimen  of   Meek  anil    Hayden)  from   Black   Hills,  South 

Dakota,     s  6. 
3c.  Cast  of  interior  of  ventral  valve,  from  Little  Rock  Mountains,  Montana,     x  6. 
3d.  Cast  of  interior  of  ventral  valve  (type  specimen   of   Meek  and  Hayden),   from 

Black  Hills,  South  Dakota. 
Fig.  4.  Dicellomits  jmlitiis 446 

4.  Interior  of  dorsal  valve,     x  6. 
4a.  Interior  of  ventral  valve,     x  6. 

Fig.  5.  Iphidea sculptiUa 447 

.5.  Summit  view  of  ventral  valve,     x  4. 
5a.  Side  view  of  fig.  5.     x  4. 

5ft.  View  of  the  broken  false  area  and  pseudo-deltidinm  of  iig.  5.     x  4. 
5c.  Surface  of  fig.  5,  greatly  enlarged. 

p'ig.  6.  Iphidea  sp.  undet 449 

6.  Dorsal  valve  described  in  the  text,     x  4. 

468 


U.  S.  OEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.    LX 


I 


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w     '     \ 


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la 


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3c 


3a 


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3cl 


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5c 


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CAMBRIAN 


THE  HELIOTYPE  PRINTING  CO.,  BOSTON 


PLATE   LXI. 


469 


PLATE    LXI. 

Page. 
Fig.  1.  BiUinijsella  colovadoensis '150 

1.  Ventral  valve,  from  Gallatin  Range,     x  2. 

la.  Dorsal  valve,  from  same  locality  as  fig.  1.     x  2. 
lb.  Interior  of  dorsal  valve,  from  same  locality  as  fig.  la.     x  3. 
Ic.  Interior  of  ventral  valve,  from  same  locality  as  fig.  1.     s  3. 
Id.  Cast  of  interior  of  ventral  valve,  Gallatin  Range,     x  3. 
Fig.  2.  Ortltis  (?)  sandbei-gi 452 

2.  Veuti'al  valve,     x  3. 
2o.  Dorsal  valve,     x  3. 

26.  Interior  of  dorsal  valve,     x  6. 
2c.  Interior  of  ventral  valve,     x  3. 
2d.  Enlargement  of  fig.  2c.     x  12. 
Fig.  3.  Orihis  remnicha - 451 

3.  Interior  of  dorsal  valve,     x  3. 
3a.  Interior  of  ventral  valve,     x  3. 

470 


U.  S.  QEOLOQICAL    SURVEV 


MONOORAPH    XXXn     PART    II     PL.   LXI 


CAMBRIAN 


THE  HELIOTVPE  PRINTING  CO.,  BOSTON 


PLATE   LXII. 


471 


PLATE    LXII. 

Page. 
Fig.  1.  Orihis  remnicha ).")  1 

1.  Rather  strongly  costate  dorsal  valve,     x  2. 
la.  Finely  costate  ventral  valve,     x  3. 

11).  Finely  costato  dorsal  valve  on  same  bit  of  rock  as  fig.  1«.     x  ,3. 
Ic.  Strongly  costate  ventral  and  dorsal  valves,     x  3. 

Id.  Dorsal  and  ventral  valves,  showing  fine  radiating  stria'  on  costic.     x  3. 
Fig.  2.  Acrotreta  gemma 449 

2.  Suuimit  view  of  ventral  valve,     x  6. 
'2a.  Posterior  view  of  ventral  valve,     x  6. 
'2b.  Side  view  of  ventral  valve. 

2c.  Summit  view  of  cast  of  interior  of  ventral  valve,     x  6. 

2d.  Uorsal  valve,     x  4. 

2e.  Interior  of  dorsal  valve,     x  6.  ' 

472 


U.  S.  OEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.    LXII 


CAMBRIAN 


THE  MELIOTVPE  PRINTING  CO.,  BOSTON 


PLATE  LXIII. 


473 


PLATE   LXIII. 

rage. 
Fig.  1.  Platyceraa  primordtalis 453 

1.  Ca^t  of  interior  of  shell. 

Fig.  2.  Hiwlithes  pi-imonliaHs 454 

2.  View  of  (lat  side  and  two  sections  of  a  large  specimen. 

2a,  Reprotliictiou  of  photograph  of  a  slab  of  sandstone,  with  numerous  specimens  of 
H.  primordialis,  from  the  St.  Croix  sandstone  of  Wisconsin.     Tho  small  shells  are 
identical  with  H.  gregaria  of  M.  and  H. 
Fig.  3.  Agnostiis  interatrictus 454 

3.  Entire  specimen,  from  Antelope  Springs,  Utah. 
3a.  Pygidinm,  from  Gallatin  Range,     x  6. 

Fig.  4.  Agnostus  bidens 455 

4.  Cephalic  shield,     x  6. 
4a.  Pygidium.     x  6. 

Fig.  5.  Agnostus  tiimidosus 455 

5.  Cephalic'shield.     x  6. 

5a.  Pygidium,  associated  with  fig.  5.     x  6. 
Fig.  6.  Hagnia  spharica  442 

6.  Reproduction  of  photograph  of  thin  section,     x  8. 

6a.  Drawing  of  thin  section,  x  9.    The  light-colored  spaces  are  the  flllingB  of  the  canals. 
They  correspond  to  the  darker  spaces  of  the  photograph. 

474 


U.  8.  OEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART  II     PL.  LXIII 


(p-? 


■S' 


4a 


3a 


5a 


CAMBRIAN 


THE  HELIOTYPE  PHINTtNfl  CO.     SOBTON 


PLATE  LXIV. 


475 


PLATE    LXIV. 

Page. 
Fig.  1.  rti/cliojMfia  (L. )  ivisconsensis ^^l 

1.  Central  portions  of  head  aiul  side  outline  of  median  section  of  head  and  occii>ital 

spine, 
la.  Free  cheek  associated  with  fig.  i. 
16.  Central  portions  of  head  of  specimen  from  the  !St.  Croix  sandstone  of  Wisconsin. 

After  Hall. 
Ic.  Pygidium  from  the  St.  Croix  sandstone  of  Wisconsin. 
Fig.  2.  Ptijchoparia  (?)  (Uademata "^^^ 

2.  Central  portions  of  head. 

2(1.  Free  check  associated  with  fig.  2. 
"  26.  Hypostoma,  associated  with  fig.  2. 
2c.  Pygidium  from  the  St.  Croix  sandstone  of  Wisconsin. 
Fig.  3.  Fttjchoparitt  .sp.  uudet ■15° 

3.  Central  portion  of  head,     x  3. 

Fig.  4.   rttjclwpuvia  Uanoensis - *58 

4.  Reproduction  of  illustration  of  the  type  specimen. 

Fig.  5.  Ptychoparia  ap.  undet ^-^^ 

5.  Central  portion  of  head  of  the  only  specimen  in  the  collection. 

Fig.  6.  Bathyiiy'isciia  sp.  undet ^^^ 

6.  Figure  of  the  specimen  referred  to  in  the  test. 

476 


U.  8.  QEOLOaiCAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.    LXIV 


CAMBRIAN 


THE  HELtOTVPE  PRINTrNG  CO..  BOSTON 


PLATE  LXY. 


477 


PLATE    LXV. 

Page. 
Fig.  1.  Arionelhia  levis 462 

1.  Central  portions  of  head  of  type  specimen,  and  side  outline,     x  4. 

Fig.  2.  Arionellus  sp.  uudet 463 

2.  Figure  of  specimen  referred  to  in  text. 

Fig.  3.  Zacanthoidea  sp.  undet 463 

3.  Central  portions  of  head,    x  5. 

Fig.  4.  Ptychoparia  penfieMi 456 

4.  Central  portions  of  head. 

4a.  Free  cheeks,  associated  in  same  layer  with  fig.  4. 
46.  Associated  pygidium. 
Fig.  5.  Crepicephalus  texanus 460 

5.  Partially  restored  drawing  from  specimens  in  the  Middle  Cambrian  shales  of  Ala- 

bama. 
Fig.  6.  Liostracua  parvua.... i 463 

6.  Central  portions  of  head  of  type  specimen,   x  6. 

Fig.  7.  Ptychoparia  aniiquata 456 

7.  Entire  individual,  slightly  restored,     x  2. 

la.  Side  outline  of  head  of  a  variety  of  this  species,     x  2. 
Fig.  8.  Ptiichoparia  ( E. )  affinia 457 

8.  Reproduction  of  figure  of  type  specimen. 

Fig.  9.  SoJenopIeura  (?)  iceedi 464 

9.  Central  portions  of  head  of  type  specimen. 

9a.  A  small  head,  showing  same  general  characters  as  fig.  9, 

478 


U.  8.  QEOLOOICAL    SURVEY 


MONOGRAPH   XXXII     PART   II     PL.  LXV 


CAMBRIAN 


THE  MELIOTfPE  PRINTIHO  CO.,  BOSTON 


Section  II.— DEVONIAN  AND  CAKBONIFEROITS  FOSSILS. 


By  Geoege  H.  Girty. 


INTRODUCTION. 


In  the  following  pages  are  described  the  Paleozoic  faunas,  with  the 
exception  of  the  Cambrian,  which  have  been  found  in  the  Yellowstone 
National  Park.  The  point  of  interest  in  this  connection  is  the  presence  of 
the  Devonian  and  the  apparent  absence  of  the  Coal  Measures  in  this  region. 
The  Ordovician  and  Silurian  are  also  absent,  and  the  only  Paleozoic  forma- 
tions indicated  by  the  collections  are  the  Cambrian,  the  Devonian,  and  the 
Lower  Carboniferous. 

The  great  bulk  of  the  material  was  furnished  by  the  Madison  limestone, 
whose  fauna,  though  showing  close  relations  only  with  that  of  the  Kinder- 
hook  period,  may  have  survived  nearly  through  the  Mississippian.  The 
fauna  is  essentially  that  described  by  White  and  by  Hall  and  Whitfield,^ 
but  it  is  more  extensive  than  that  recorded  by  them. 

Devonian  types  are  rare  and  constitute  a  fauna  more  scanty,  though 
nearly  akin  to  that  described  by  Meek  and  by  Walcott  from  the  Rocky 
Mountain  region  of  Nevada. 

The  collections  which  I  have  had  the  privilege  of  examining  were 
made  by  the  geologists  of  the  Yellowstone  National  Park  survey,  whose 
careful  stratigraphic  observations    rendered  easier  the    solution    of  many 

'As  is  well  known,  the  principal  literature  dealing  with  the  paleontology  of  the  Devonian  and 
Lower  Carboniferous  in  the  Rocky  Mountain  region  consists  of  a  report  by  Meek  and  another  by  Hall 
and  Whitfield  in  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV,  1877;  a  report  by  White  in  Wheeler's 
Expl.  and  Surv.  W.  100th  Merid.,  Vol.  IV,  1875;  and  a  monograph  by  Walcott,  Hon.  U.  S.  Geol. 
Survey,  Vol.  VIII,  Pal.  Eureka  District,  1884. 

Meek  has  also  identified  certain  Mississippian  horizons  in  this  region:  Prelim.  Rept.  U.  S.  Geol. 
Surv.  Wyoming,  etc.,  Hayden,  Fourth  Ann.  Kept.,  1871,  p.  288;  ibid..  Fifth  Ann.  Rept.,  p.  76;  ibid., 
Sixth  Ann.  Rept.,  pp.  432-433. 

479 


480  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

problems  that  would  otherwise  have  been  left  in  doubt.  To  them  I  desu'e 
in  this  place  to  make  ample  acknowledgments,  and  especially  do  I  wish  to 
express  my  obligation  to  Mr.  Charles  Sclmchert,  of  the  United  States 
National  Museum.  A  preliminary  study  of  this  collection  Avas  made  by 
him  before  the  work  was  assigned  to  me,  and  he  also  supplied  me  with  facil- 
ities in  the  National  Museum,  gave  me  free  access  to  the  Museum  collec- 
tions for  comparison,  permitted  the  use  of  his  Bibliography  of  North  Amer- 
ican Brachiopoda,  then  unpublished,  and  placed  at  my  disposal  his  fine  col- 
lection of  brachiopods  and  his  no  less  extensive  knowledge  of  the  same.  It 
gives  me  pleasure  also  to  acknowledge  my  obligations  to  Mr.  John  L. 
Ridgway,  by  whom  the  greater  number  of  the  drawings  accompanying 
this  report  were  made. 

DEVONIAN. 

The  inaiterial  believed  to  be  of  Devonian  age  is  unsatisfactory  in  that 
it  is  scanty  and  often  poorly  preserved,  while  the  species  represented  are 
almost  the  worst  that  could  have  been  selected  for  stratigraphic  correla- 
tion. Consisting  mostl}^  of  corals,  with  a  few  gastropods  and  brachiopods, 
it  would  be  difficult,  unassisted  by  the  richer  though  related  fauna  of 
Nevada,  to  affirm  of  some  of  the  local  representations  anything  more  than 
that  they  are  older  than  the  Carboniferous  and  younger  than  the  Ordovician. 
The  strata  represented  fall  into  three  groups,  distinguished  somewhat  by 
their  lithologic  character  as  well  as  by  the  fossils  which  they  carry.  More 
extensive  collections  would  probably  show  a  closer  connection  than  now 
appears. 

The  age  of  the  exposure  on  the  north  side  of  Soda  Butte  Creek  has 
not  been  detinitely  ascertained.  It  is  represented  only  by  an  undetermined 
species  of  Favosites,  in  a  fragmentary  condition.  The  most  likely  reference 
would  be  to  the  Silurian  or  Devonian,  for  if  Carboniferous  the  coral  belongs 
to  none  of  the  few  related  species  known  in  Cai-boniferous  rocks.  The 
locality  is  therefore  provisionally  referred  to  the  Devonian,  since  no  fossils 
of  Silurian  age  have  been  recognized  in  the  Yellowstone  Park. 

The  locality  at  Wall  Canyon,  Clark  Fork  Valley,  stands  by  itself. 
It  is  represented  only  by  Pleiirotomaria  isaacsi  {f)  (a  solitary  specimen),  both 
fossil  and  matrix  being  highly  siliceous.  P.  isaacsi  was  described  from 
Lower  Devonian  strata,  probably  of  the  age  of  tlie  Schoharie  grit,  but  its 
range  is  not  known,  and  my  identification  is  questionable. 


DEVONIAN  FOSSILS.  481 

Fntiii  the  base  of  the  bluff  nn  Little  Sunlight  Creek  only  Atrypa  reticu- 
laris is  known,  a  small  coarsely  plicate  variety.  It  is  similar  to,  perhaps 
identical  with,  the  type  figured  b>-  Walcott  (Mon.  U.  S.  Geol.  Survey,  Vol. 
VllI,  1884,  PI.  XIV,  figs,  (j,  it(t,  (!/;),  and  mentioned  as  occurring  in  the 
upper  part  of  the  formation  (p.  150).  Meek  cites  the  same  form  (King's 
Kept.  U.  S.  Geol.  Exi)l.  4()th  Par.,  Vol.  IV,  1877,  p.  3:»)  from  Pinon  Station, 
Treasure  Hill,  White  Pine  district,  etc.,  and  figures  it  on  PI.  Ill,  figs.  6,  Ga. 

The  horizons  of  Bighorn  Pass,  Gallatin  Range,  near  the  divide  between 
Gallatin  Valley  and  Panther  Greek;  the  east  slope  of  Antler  Peak,  Galla- 
tin Range;  and  the  south  slope  of  the  same,  can  be  correlated  with  one 
another  and  constitute  a  separate  group.  The  matrix  is  a  calcareous  sand- 
stone; and  the  included  fossils,  almost  exclusively  corals,  are  cnxdely  silici- 
fied.  The  common  fossils  are  Cladojiora  si).,  PachuphjUum  s]).,  CyathophyJlHm 
ccespitosum  (?),  and  Actinostroma  sp.  Every  indication  points  to  the  Devonian 
age  of  this  bed.  The  genus  Actinostroma  is  characteristic  of,  though  not 
restricted  to,  Devonian  rocks.  Ci/afhopJu/Uitm.  ccBspifosiim,  as  identified  in 
this  country,  occurs  in  Upper  Helderberg  strata.  The  genus  Pachyphyllum 
is  characteristically  Devonian,  and  Claclopora  sp.  is  more  closely  related  to 
certain  Upper  Helderberg  forms  than  to  aijy  I  have  found  described. 

The  material  from  the  south  side  of  Soda  Butte  Creek,  northeast  of 
Abiathar  Peak,  Absaroka  Range,  from  northwest  of  Abiathar  Peak,  Soda 
Butte  Canyon,  and  from  the  north  side  of  saddle  west  of  Mount  Miller, 
Absaroka  Range,  represents,  perhaps,  the  same  horizon  as  that  from  The 
Gate,  Fossil  Hill,  and  Eureka  district,  whose  fauna,  as  described  by  Meek 
and  by  Walcott  (loc.  cit.),  is  quite  similar,  as  far  as  it  goes.  In  the  Yellow- 
stone Park  this  consists  of  Atrypa  missoiiriensis,  Spirifer  eiigehnanni,  Athyris 
vittata  var.  triplicata  n.  var.,  PJeurotomaria  (f)  sp.,  PacliyphyUum.  sp.,  Cyatho- 
phyUiim  ccespitosum  (f),  etc.  Atrypa  missouriensis  is,  I  believe,  the  same  form 
figured  by  Walcott  as  A.  desquaniata  Sow.  (loc.  cit.  PI.  XIV,  figs.  4,  4«),  and 
by  Meek  as  A.  reticularis  var.  As  in  their  collections  A.  missouriensis  was 
associated  with  the  small,  coarsely  plicate  Atrypa,  which  I  have  found  alone 
at  Little  Sunlight  Creek,  it  might  perhaps  be  better  to  regard  the  latter  as 
forming  one  of  the  group  of  localities  under  consideration.  This  group,  on 
the  other  hand,  is  connected  with  the  otlier  previously  mentioned  (Bighorn 
Pass  and  Antler  Peak)  by  having  in  common  CyathophyUiim  ccBspitosiun 
(doubtful  identification)  and  Atrypa  missouriensis.     A  bed  at  the  south  side 

MON  XXXII,  PT  II 31 


482  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  Soda  Butte  Creek,  northeast  of  Abiathar  Peak,  Absaroka  Eaiige,  is  unique 
in  the  collection,  and  may  fitly  be  called  a  gastropod  limestone.  The  rock 
consists  of  comminuted  organic  remains  cemented  by  a  shaly  limestone,  and 
carrying  certain  small  gastropods  in  great  abundance.  Two  of  the  types 
represented  are  described  below,  under  the  names  of  PJafystoma  minutmn 
and  Loxonema  deUcatum,  but  the  others,  of  which  there  are  perhaps  three  or 
four  genera  and  some  half  diizen  species,  are  too  jjoor  for  either  identification 
or  description.  They  ai-e  small,  and  nearly  all  badly  eroded,  and  often 
concealed  by  a  matrix  from  which  they  are  not  easily  separated.  It  has 
therefore  proved  difficult  or  impossible  to  acquire  data  even  for  certain 
generic  references ;  but  Loxonema,  Pleurotomaria,  Murchisonia,  Platystoma, 
and  perhaps  other  genera  are  probably  present.  The  associated  brachiopods 
show  this  fauna  to  be  of  Middle  Devonian  age. 

It  can  be  affirmed  beyond  question  that  all  the  localities  here  discussed 
occur  below  the  Carboniferous.  Indeed,  there  is  a  decided  faunal  break 
between  them  and  the  great  series  of  beds  regarded  as  representing  the 
base  of  that  formation,  so  much  so  that  the  two  groups  have  not  a  single 
species,  and  scarcely  even  a  single  genus,  in  common.  •  At  the  same  time, 
I  believe  that  the  lower  series  is  neither  wholly  nor  in  part  Silurian,  but 
that  it  was  in  fact  laid  down  in  Lower  or  ]\Iiddle  Devonian  time,  repre- 
senting the  Hamilton,  or  perhaps  the  Upper  Helderberg,  of  the  New  York 
system.  Many  of  the  generic  identifications  strongly  suggest  a  Devonian 
facies,  or,  at  worst,  are  ambiguous,  while  the  specific  references,  though 
often  doubtful,  all  point  to  the  Devonian  rather  than  the  Silurian  age  of 
these  strata.  Finally,  the  fauna  seems  to  be  rather  closely  related  to  that 
of  the  White  Pine  district,  etc.,  above  referred  to,  of  which  Meek  says 
(loc.  cit.,  p.  6):  "Hence  Ave  can  not  doubt  that  these  beds  belong  to  the 
Devonian,  and  probably  to  about  the  horizon  of  the  Hamilton  group  of 
the  New  York  series." 


DEVONIAN  AND  LOWER  CAKBONIFEliOUa  FOSSILS. 


483 


Table 

vonian  species. 

•2 

>?5  c 

i 

1 

S 

=5 

a 

Gallatin 
er  Creek, 
llntin  Ka 

P4 

^  a 

5": 

M 

P 

o 
a:   . 

II 

Species. 

His 

n? 

§53 

•-.5 

■S.3 

^"^i 

-<1S 

S:^ 

1*5 

g.^ 

B£S 

C3 

o  A 
"^^ 

*s« 

!l 

^" 

•a 

<§ 

P4 
2  >.ft 

So 

09 

•s-j 

12£ 

®3 

II 

0) 

"fa 

^ 

.t^M 

9 

SS<! 

g 

o 

SSM 

n 

a 

w 

m 

m 

k; 

a 

t^ 

Actiiiostrouifi  sp...... 

X 
X 

X 
X 

X 

1 

? 

X 

Favosites  sp    

X 

Spiriler  engelmaniii 

X 

X 

X 

X 

Atrvpii  reticularis .   . 

X 

X 

Pleiirotomaria  (?)  sp 

X 

X 

[ 

X 

Loxouema  delicatum  n.  s^) 

X 

LOWER   CARBONIFEROUS. 

The  Madison  limestone  has  been  divided  by  the  geologists  of  the 
Survey,  upon  lithologic  characters,  into  nine  beds,  ranging  from  24  to  32, 
both  inclusive,  of  their  section  scheme.  The  following  table,  representing 
in  condensed  form  the  sti'atigraphic  succession  ascertained  in  the  Yellow- 
stone National  Park,  was  kindly  supplied  by  Mr.  Arnold  Hague,  geologist 
in  charge  of  the  Yellowstone  National  Park  survey: 

Quadrant  quartzite. 
Madison  limestone. 

Bed.  Peet. 

32.  Four  strata  of  light-gray,  more  or  less  cberty  limestone 655 

31.  Gray  banded  limestone,  with  abundant  fossils 400 

30.  Massive  light-gray  limestone 65 

29.  Light- gray  and  brown,  very  finely  crystalline  or  granular  limestone 85 

28.  Limestone,  crystalline,  light  gray  and  generally  massive 200 

27.  Limestone,  dark  gray  and  butt",  very  argillaceous,  thick  and  thin  bedded. . .  50 
26.  15  feet  of  quite  pure  and  60  feet  of  thin-bedded  argillaceous  limestone, 

both  containing  fossils 75 

25.  Coarsely  crystalline,  dark-gray  limestone 80 

24.  Limestone,  finely  crystalline  and  massive  below,  cherty  in  its  upper  portion . .  60 

Total 1 ,  670 

Three  Forks  limestone. 


484 


GEOLOGY  OF  THE  YELLOWSTO^TE  NATIONAL  PARK. 


All  the  evidence  available  seems  to  indicate  that  the  Madison  limestone 
is  faunally  a  unit  and  can  not  be  subdivided  on  the  basis  of  its  contained 
fossils. 

Although  the  fauna  comprises  many  Kinderhook  species,  I  doubt 
whether  it  can  justly  be  regarded  as  representing  the  Kinderhook  alone; 
possibly  it  is  equivalent  to  the  major  portion  of  the  Mississippian.  The 
exact  correlation  of  this  fauna  has  proved  impossible,  but  its  affinities 
seem  to  be  rather  with  the  Kinderhook  than  with  any  other  division  of  the 
Lower  Carboniferous. 

The  following  table  represents  the  various  species  of  invertebrates 
recognized  in  the  Madison  limestone  and  their  range  through  the  nine  beds 
whose  character  and  succession  have  just  been  described.  The  table  is 
defective  in  that  a  number  of  localities  from  which  collections  were  made 
have  not  been  located  in  the  section  scheme  previously  given,  and  conse- 
quently the  data  so  furnished  could  not  be  tabulated.  And  again,  the 
collections  from  many  localities  are  so  meager  as  not  to  contain,  probably, 
many  of  even  the  commoner  species.  Other  sources  of  error  exist  in  the 
possibility  of  incorrect  reference  of  the  localities  to  their  true  horizon  in  the 
section,  and  of  mistaken  identifications  in  the  course  of  paleontologic  work. 
]Mucli  care  has  been  taken  to  minimize  both  these  sources  of  error,  and  it  is 
believed  that  the  accompanying  table  is  a  fair  statement  of  the  character 
and  range  of  the  fauna  of  the  i\Iadison  limestone. 

Table  showing  the  range  of  Lower  Carboniferous  species. 


Number  of  bed. 


Species.                                       1 

24 

25 

26 

27 

28 

29 

30 

31 

32 

X 

X 

X 

X 

X 

X 

X 

X 
X 

Aff nniihvlliiui  ( 'f^  e\c;ivatuni  n  ST) 

X 

X 

X 
X 
X 

X 

X 

Clisiophyllum  teres  n.  sp 

X 

X 
X 

X 

X 
X 

X 

? 

X 

Anisotrypa  sp 

X 

LOWER  CARHONIFEROUS  FOSSILS.  485 

Table  showing  the  range  of  Lower  Carboniferous  species — Contiuued. 


Niinilier  of  bed. 

U 

25 

26 

27 

28 

29 

30 

31 

32 

Kridonora  (  f ^  st> 

X 

X 

X 



X 

X 

X 
X 

Ovtliotlietes  init'Oiifilis              .   

X 

X 

X 

X 

X  !   X 

X 

X 

Derbva  keokuk  (?>    

X 

Lept;i*na  rhoniboidalis 

X 
X 
X 

X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 

X 

X 

X 

X 

X 

X 
X 

X 

X 

X 

Profliictt'lla  coonereiisis 

X 

Pi'oductGlla  alitera  ii.  8d 

Prodiictua  scabriculus                          ..... 

^ 

X 

X 

X 
X 

X 

X 

PiNKluctus  ijallatineii.sis  n.  80                    -  .. 

X 
X 
X 

X 

X 
X 

X 
X 
X 

X 
X 
X 
X 
X 

X 
X 

X 
X 

X 

Procluctus  semireticulatus      .   ...   ........ 

X 

Catuarotcechiii  herrickana  11.  sp  ....  ......-- 

X 
X 

X 
X 

Camarotoecliia  luetallica -. 

X 


X 
X 

X 

X 

Camarotfpcliia  sappho  (?) 

X 

X 

X 

Caniarotcechia  sp 

X 

... 

Liorhy nchus  haguei  n.  sp 

X 
X 
X 
X 

...-.- 

Dielasma  utab 

X 

X 
X 
X 
X 

X 
X 
X 
X 

X 

X 
X 

X 
X 

X 
X 

X 
X 

Spiiifer  centroiiatus 

Spiriferceutrouatusvar.  semifurcatusu.var 

Spiiifer  subattenuatus 

Spiiifer  sp 

X 

Spirifer  marionensiB(?) _   

X 

Spirifer  sp 

X 

Spirifer  striatus  var.  madisonensis  n.  var. . . 

X 
X 
X 

Martinia  rostratan.  sp 

X 
X 
X 

X 
X 

X 
X 

X 
X 

X 
X 

X 

IJeticularia  cooperensis 

X 
X 

X 

Eeticularia  cooperensis  var 

Reticularia  ( ?)  peculiaris 

X 

X 

Eeticularia  (?)  subrotuntTata 

Syringotliyris  carteii 

X 

X 

486  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  showing  the  ranye  of  Lower  Carboniferous  species — Coiitiuued. 


Species. 

Number  of  bed. 

24 

25 

26 

27 

28 

29 

30 

31 

32 

Eumetria  venieuiliaua 

X 

X 

X 

X 

X 

X 

f 

X 

Seminula  madisonensis  vav.  pusilla  u.  var. 
Spiiiinnln,  liuiiiilis  ii.  sv)           

X 
X 
X 

X 
X 
X 

X 
X 

X 

X 
X 

X 

X 

Cliotbyris  crassicardinalis 

Cliothyris  crassicardiiialis  var.  nana  u.  var. 

X 
X 

X 

X 

X          X 

X 

X 

X 

Conocardiuiu  pulchellum  { ?) 

i 

X 
X 



X 
X 

X 

X 

X 

X 
X 
X 

X 

The  following  data  are  derived  from  the  table  just  given,  and  go  to 
show  that  the  Madison  limestone  fauna  is  practically  a  unit,  evincing  very- 
little  progressive  differentiation,  and  not  affording  sufficient  evidence  to 
warrant  its  subdivision  upon  paleontologic  considerations. 

Seventy-nine  species  have  been  recognized  in  the  nine  beds  which  go  to 
make  up  the  formation.  Of  these,  4  species  have  not  been  assigned  to  any 
particular  lied,  because  it  has  not  been  ascertained  what  position  the  locali- 
ties from  which  they  came  would  occupy  in  the  type  section.  These,  with 
5  species  of  Platyceras  and  5  of  Fenestella,  have  not  been  taken  into  con- 
sideration in  collecting  the  following  data.  Therefore  only  65  species  have 
been  considered  in  making  up  the  tables  from  which  these  data  are  sup- 
plied. Of  these  65  species,  29  are  found  to  be  rare  and  scattered  among 
single  beds,  but  some  17  or  18  are  common,  and  may  be  said  to  range 
from  the  bottom  to  the  top  of  the  formation. 

If  the  nine  beds  constituting  the  Madison  limestone  be  artilicially  divided 
into  three  groups  of  three  beds  each,  the  central  group  is  represented  by  38 
species,  only  6  of  which  are  not  found  in  the  upper  or  the  lower  group, 


LOWER  CA1U50NIFEK0US  FOSSILS.  487 

wliili'  tlu'  uppiT  Madison,'  represented  by  33  species,  and  tlie  lower  Madi- 
son by  47  species,  have  21  species  in  common.  In  other  words,  64  ))er 
cent  of  the  forms  found  in  the  lowest  beds  occur  also  in  the  middle  beds, 
wliile  45  per  cent  survive  into  the  upper  beds;  (iO  per  cent  of  those  in  tlie 
middle  beds  are  found  also  in  the  upper,  and  64  per  cent  of  those  in  the 
upper  are  introduced  in  the  lower  Madison.  These  percentages  include 
spet'ies  which  were  found  in  only  a  single  locality,  and  which,  though  per- 
haps alien  to  the  beds  in  which  they  are  not  recorded,  at  the  same  time 
can  not  be  said  to  be  characteristic  of  that  which  alone  provided  them. 
Although  the  table  (see  p.  484)  shows  a  number  of  species  in  the  upper 
portion  of  the  Madison  which  have  not  yet  been  found  in  the  beds  below, 
it  would  scarcely  be  tiiie  to  say  that  they  materially  changed  its  character. 
The  fauna  of  the  Madison  limestone  is  closely  related  to  that  which 
was  described  in  reports  by  White,^  by  Hall  and  Whitfield,^  and  probably 
also  by  Meek.*  The  close  relationship  of  this  fauna  with  that  of  the 
Kinderhook  formation  of  the  Mississippi  Basin  was  recognized  by  the 
authors  mentioned.  Writing  in  regard  to  this  correlation  in  1877,  White 
says  (loc.  cit):  "The  collections  of  the  expedition  contain  fossils  from 
only  three  localities  that  I  have  definitely  referred  to  the  sub-Carboniferous 
period.  These  localities  are  Mountain  Spring,  Old  Mormon  road,  Nevada ; 
Ewells  Spring,  Arizona  (upper  horizon),  and  a  place  below  Ophir  City, 
Utah.  The  collection  made  at  the  first-named  locality  is  the  most  charac- 
teristic and  important  one  of  all,  and  is  referred  to  the  horizon  of  the 
Kinderhook  formation,  to  which  horizon  it  is  not  improbable  the  others  also 
belong."  And  again:  "The  case  is  far  different,  however,  with  the  collec- 
tion from  the  Mountain  Spring  locality,  which  I  refer  without  hesitation  to 


I  In  makiDg  out  these  percentages  certain  species,  as  f:ir  as  my  data  go,  are  fonnd  to  have  skipped 
one  or  more  beds  in  vertical  distribution.  In  such  case  the  species  Iiave  been  counted  as  occurring 
uninterruptedly  between  the  points  of  highest  and  lowest  occurrence. 

2  Wheeler's  Rept.  U.  .S.  Geog.  Surv.  W.  100th  Merid.,  Vol.  IV,  1M77,  pp.  12-17,  p.  79  et  seq. 

'King's  Rept.  Geol.  Expl.  40th  Par.,  Vol.  IV,  1877,  p.  2.51  et  seii. 

■•Hayden,  1873,  Prelim.  Rept.  U.  S.  Geol.  Snrv.  Wyoming,  etc.,  Sixth  Ann.  Rept.  (for  1872),  pp. 
432-433.  Meek  here  cites  a  fauna  from  Mystic  Lake ;  canyon,  e.ast  side  of  Madison  River ;  Bridger  Peak 
near  Fort  Ellis;  Blacktail  Deer  Crrek,  north  side  of  Gros  Ventres  Butte:  Flathead  Pass,  north  side 
Henrys  Lake;  canyon  west  of  GalLitin  River  (all  in  Montana),  and  Camp  19,  Idaho,  of  which  he 
says  (p.  433) :  "  In  looking  over  the  collections  from  these  localities  I  have  been  quite  impressed  with 
the  similarity  of  their  geueral  focies  ( without  being  quite  sure  that  any  of  the  species  are  identical)  to 
the  fauna  of  the  Waverly  group  of  Ohio,  now  known  to  belong  to  the  Carboniferous."  Most  of  these 
localities  are  in  the  vicinity  of  Yellowstone  National  Park,  and  probably  are  in  the  Madison  lime- 
stone. 


488  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  Kiiidei-liook  g-roup"  (p.  14).  The  fauna  of  this  locaUty  seems  to 
include  the  following  species :  PJaUjcrinus  sp.,  Actinocnnm  viaticus,  Pro- 
ductiis  })arvus,  Strophomena  rhomboidaUs,  Spirifer  centronatus,  S.  striatus, 
S.  extenuatus,  S.  (Martinia)  pecidiaris,  Spirigera  monticola,  S.  ohmaxima,  Tere- 
hratula  (Dielasma)  hnrUngtonensis.  The  Madison  limestone  contains  the 
following  equivalent  or  identical  species :  Platycrinus  symmetricus  of  the 
same  type  as  the  form  figured  by  White ;  Prodiwtus  parviformis  n.  sp.,  con- 
sidered to  be  different  from  P.  jyarvus  M.  and  W.,  but  the  same  as  P.  parvus 
White;  Leptcena  rhomhokkdis ;  Spirifer  centronatus;  S.  striatus  var.  madison- 
ensis  n.  var.,  which  I  believe  to  be  varietally  different  from  S.  striatus  of 
White,  though  corresponding  to  it  in  the  fauna :  Syringothyris  carteri,  repre- 
senting the  closely  related  S.  extenuatus^  oi  Whita's  fauna;  Beticularia  (f) 
peculiaris ;  Athyris  incrassata.- 

Dielasma  utah,  which  I  ha-s'e  recognized  in  the  Yellowstone  National 
Park  collections,  is  probably  the  same  as  D.  hurUngtonense ;  at  least,  with 
the  limited  material  at  my  command,  I  am  unable  to  find  any  characteristic 
difference.  Some  of  the  species  from  the  other  localities  also  have  their 
analogues  in  the  Madison  limestone  fauna.  S.  harveyi  White  may  be  one 
of  the  two  species  of  Syringopora  described  below,  although  the  original 
description  is  insufllcient  for  identification.  Conocardium  pukhellum  (f)  of  this 
report  is  certainly  of  the  same  type  as,  and  may  be  identical  with,  C. 
trigonak  White,  which  is  unfortunately  unidentifialjle,  while  Euomphahis 
luxus  is  represented  by  Straparollus  titahensis,  both  closely  allied  forms. 

Hall  and  Whitfield  also  describe  a  similar  fauna  from  the  limestone  of 
Dry  Canyon,  Oquirrh  Mountains;  and  from  Ogden,  Little  Cottonwood,  and 
Logan  canyons,  in  the  Wasatch  Range,  Utah.  This  fauna  is  described 
and  figured  under  the  name  of  the  Waverly  group,  and  is  said  (loc.  supra 
cit.,  p.  201)  to  contain  an  assemblage  of  fossils  considered  to  be  "of  about 
the  age  of  the  Waverly  group  of  Ohio'  and  the  yellow  sandstones  of  Bur- 


'  Some  of  the  specimens  which  I  have  identified  as  S.  carteri  can  not  be  said  to  differ  in  any 
essential  particular  from  that  figured  by  White  as  S.  extenuatus. 

=  This  form  is  very  close  indeed  to  White's  Spirigera  ohmaxima  in  form  and  general  characteristics. 
Strictly  speaking,  A.  incrassata  is  a  true  Athyris,  while  Spirigera  ohmaxima  belongs  to  the  subgenus 
Cliotliyris.  In  point  of  fact  I  have  not  been  able  to  discover  spines  on  White's  specimens,  and  they 
may  prove  to  bo  the  same  as  the  form  which  I  have  called  J.  incrassata. 

■'The  Waverly  group  of  Ohio  is  now  known  to  be  composite  in  its  nature  and  to  contain  several 
different  faunas.  The  lower  portion,  Herrick  has  been  led  to  believe,  is  Devonian,  and  the  upper 
portion  corresponds  to  the  Kinderhook  and  the  Burlington-Keokuk  phases  of  the  Mississippian.  A 
close  acquaintance  with  the  Waverly  faunas,  involving  several  years  of  collecting  and  study,  has 
convinced  me  that  Herrick  is  altogether  mistaken  iu  this  view.     The  whole  of  the  Waverly,  including 


LOVVliR  CARBONIFEROUS  FOSSILS.  489 

lino-ton,  Iowa,  wliirli  li:i\X'  been  referred  to  the  same  aj'e.'"  The  foHowing 
species  are  described  as  "Fossils  of  the  Waverly  <iroup:"  Michelina  sp., 
StreptorhiJHchus  equivalvifi,  S.  Infiatus,  Sfrophomeua  rhomhoidaUs,  Chonetes 
hganensis,  Spirifera  centrotiata,  S.  alha-pinmsis,  Athyris  daytoni,  A.  planosid- 
caia  (.'),  Rhynclwnellapnstnlom  (.*'),  Tcrehraiula  ntah,  Euomphalus  (StraparoUns) 
utahensis,  E.  laxas,  E.  (StrapafoUHs)  opJiireiisis,  Proetiis  peroccidens,  P. 
hyancusis.  The  followin<>-  may  be  mentioned  as  identical  or  cognate  forms 
occurring-  in  the  Madison  limestone:  Mkhelinia  placenta  (probably  the  same 
as  MichcUnia  sp.  of  Hall  and  Whitfield's  report),  Orthothetes  incequalis  (the 
same  as  Streptorhynchus  equivalvis),  Leptmna  rhomhoidalis,  Chonetes  loganensis, 
Spirifer  centronatus  (S.  alha-pinensis  seems  to  be  only  an  insignificant  varia- 
tion from  this  form),  Martinia  rostrata  n.  sp.  (the  same  as  Athyris  planosid- 
cata  (J)  of  Hall  and  Whitfield),  Camarotachia  metaUica  (the  same  form  -which 
Hall  and  Whitfield  identify  as  Rhynchonella  piistidosa  (f)  ),  Bielasma  utah, 
Straparollus  utahensis,  Proetus  peroccidens,  and  P.  loganensis.  Of  the  forms 
grouped  vmder  the  heading  "Fossils  of  the  Lower  Carboniferous"  (p.  265), 
Productus  semireticidatus,  P.  Icevicosta,  and  Spirifera  setigera  (probably  the 
form  recognized  below  as  Eeticidaria  cooper ensis  var.)  are  found  in  the 
Madison  limestone. 

]\Ieek'  cites  a  fauna  from  various  localities  in  Montana  and  one  in  Idaho 
which  is  probably  identical  with  that  of  the  Madison  limestone.  The  lists 
which  accompany  this  notice  are  of  a  preliminary  character,  and  but  few 
species  are  identified  specifically.  Still,  the  genera  involved,  together  with 
such  brief  descriptions  as  are  appended,  as  well  as  the  close  relation  geo- 
graphically of  his  localities  to  the  Yellowstone  National  Park,  i-ender  it 
probable  that  he  was  dealing  with  the  Madison  limestone  fauna.  Meek 
expresses  himself  as  being  impressed  with  the  similarity  of  its  general  facies 
to  that  of  the  Waverly  group  of  Ohio. 

The  faunal  lists  given  by  Peale^  constitute  essentially  the  same  fauna 

the  Bedford  shale  and  .iscending  to  its  hitest  stratum,  is  undoubtedly  Carboniferous.  The  fauna  of 
the  Cuyahoga  shale,  using  the  term  to  include  the  outcrops  at  Lodi,  Medina,  Bagdad,  Weymouth,  and 
the  lower  (?)  beds  at  Riclitield,  which  Herrick  wishes  to  refer  to  the  Devonian,  is  certainly  the  same 
as  that  of  the  Chouteau  limestone,  which  Meek  includes  as  typical  in  his  description  of  the  Kinderhook 
period  (Am.  Jour.  Sci.  (2),  Vol.  XXXII,  18(il.  pp.  169  et  seq.,  288).  Above  the  Cnyahoga  shale  follow 
representatives  of  the  Hurlington  and  Keokuk  horizons. 

It  is  probably  that  portion  of  the  Waverly  faunas  which  is  found  in  the  Cuyahoga  shale  that 
Hall  and  Whitfield  have  in  mind  in  this  reference,  as  they  mention  the  yellow  sandstones  of  Burling- 
ton, which,  with  the  Chouteau  limestone,  are  supposed  to  be  typical  Kinderhook. 

'Sixth  Ann.  Kept.  U.  S.  Geol.  Surv.  Wyoming,  etc.  (loc.  cit.,  pp.  432-433,  465  et  seq.) 
^The  Paleozoic  section  in  the  vicinity  of  Three  Forks,  Montana:  Bull.  U.  S.  Geol.  Surv.  No.  110 
1893,  pp.  33-39. 


490  GEOLOGY  OF  THE  YELLOWSTOXE  NATIONAL  PAEK. 

as  that  of  the  Madison  limestone,  and  had  the  material  been  worked  hj  the 
same  hand  the  specific  determinations  wonld  doubtless  have  been  more 
uniform.     The  two  areas  are  geographically  closely  related. 

Considering  the  favina  of  the  Madison  limestone  as  a  whole,  it  can  be 
pointed  out  that,  of  the  79  species  known  from  this  formation,  29  were 
described  from  or  have  been  identified  in  Kinderhook  beds  of  Ohio,  Michi- 
gan, and  the  Mississippi  Valley — that  is,  aljout  37  jier  cent  of  the  Madison 
limestone  fauna  consists  of  Kinderhook  species.  These  are:  JliclieUnia 
placenta,  Platycrinus  symmetricus,  Cra/nia  Icevis,  Rhipidomella  michelini,  Orfho- 
thetes  incequalis,  Berbija  keokuk  (f),  Leptcena  rJiomhoidalis,  Chonetes  loganensis,^ 
Chonetes  ornatus,  Productella  cooperensis,  Prodiictus  Icevicosta,  P.  semireticu- 
latus,  Camaroplioria  ringens,  CamarotcecMa  herrickana  n.  sp.,  C.  metaUica, 
C.  cainarifera  (.**),  C.  sappho  (.''),  Dielasma  utah,^  Spiriferina  solidirostris, 
Spirifer  centronatus,  S.  suhattenuatus,  S.  marionensis  (.^),  Betkidarla  cooper- 
ensis,  B.  (.^)  2>'^culiaris,  R.  (f)  suhrotimdata,  Syringotliyns  carteri,  Athyris 
lameUosa,  Cliothyris  crassicardinaUs,  and  Conocardium  pulchelluin  (.**). 

After  making  the  necessary  deductions  from  this  list,  some  of  whose 
identifications  are  rather  in  the  nature  of  approximations,  it  still  niust  be 
apparent  that  the  fauna  of  the  Madison  limestone  has  many  peculiarities  of 
the  earlier  Mississippian,  and  in  particular  shows  a  marked  affinity  through- 
out with  the  Kinderhook  fauna. 

Taking  a  more  general  view  of  the  fauna,  the  presence  of  Syrinr/othyris 
speaks  for  lower  Mississippian,  since  it  is  not  known  there  above  the  Keokuk, 
and  the  same  is  true  of  Leptcena  rhomhoidalis,  since  it  does  not  occur  above 
the  lower  Burlington.  It  umst  be  noted,  however,  that  these  forms 
appear  to  be  restricted  to  the  lower  portion  of  the  ]\Iadison  also.  The 
absence  of  Productus  punctatus  from  this  formation  is  evidence  in  the  same 
direction,  as  it  is  introduced  in  America  in  the  Keokuk,  and  in  general 
there  is  to  be  noticed  in  the  Madison  limestone  fauna  an  absence  of  those 
highly  difi'erentiated  and  often  peculiar  species  which  characterize  the 
beds  of  the  middle  and  upper  Mississippian.  This  is  perhaps  most  noticeable 
in  the  Spiriferoids  and  Productoids,  for  they  are  the  conunonest  forms.  In 
the  Madison  tliese  comprise  a  few  comparatively  simple,  stable,  and  persistent 


'A  form,  probably  the  same,  is  common  in  the  Cuyahoga  shale  of  northern  Ohio,  passing  usually 
as  C  ilUnolsenais. 

•Probably  a  synonym  for  /'.  hiirUinjtoiieiise. 


LOWER  CARBONIFEROUS  FOSSILS.  491 

forms,  often  real  Kin<lerlio<)k  types,  wliicli,  however,  do  not  jiass  over  into 
the  hij-'hly  developed  and  ditierentiated  speeies  l^elonging  to  the  same  genera 
in  tlie  Mississippi  Valley  in  Bnrlington  time  and  later. 

On  the  other  hand,  several  genera  in  the  Madison  limestone  show  by 
their  presence  that  we  are  not  dealing  with  a  pure  Kinderhook  fauna. 
Here  must  be  mentioned  the  genera  Archimedes,  Martinia,  Seminula,  and 
Endothyra.  Archimedes  is  not  known  below  the  Keokuk,  nor  Endothyra 
below  the  Warsaw,  Species  of  Seminula  have  been  described  from  the 
Kinder! look,  and  Martinia  is  well  represented  in  the  Devonian,  occurring 
also  in  the  Mississippian  and  Coal  Measures ;  but  an  experience  of  several 
years  in  the  Waverly  group  of  Ohio  and  adjacent  States  seems  to  confirm 
the  statement  that  these  genera  are  rare  indeed  in  the  Kinderhook  fauna. 
It  is  significant  that  in  the  ^ladison  limestone  Archimedes  and  Endothyra 
are  found  only  in  the  upper  portion,  while  Seminula  and  Martinia  range 
throughout. 

Such  species  as  Derhja  keokuk  (F),  Camarophoria  rimjens,  Camarotcechia 
metallica,  and  Eumetria  verneuiliana  demand  individual  consideration  in 
discussing  the  age  of  the  Madison  limestone. 

If  Rliynclwuella  metallica  was  really  .originally  found  in  Upper  Carbon- 
iferous rocks,  either  it  must  have  an  extraordinarily  long  range  or  else 
this  is  an  instance  of  the  danger  in  making  identifications  on  external 
characters  from  a  single  specimen;  for  between  the  type  and  the  material 
from  the  Madison  limestone  I  can  find  no  specific  distinction. 

Berhya  keokuk  (f),  whose  identification  is  based  upon  a  single  poorly 
preserved  specimen,  is  known  in  Indiana  associated  with  Syringothyris 
and  a  Waverly  fauna.  While  Eumetria  verneuiliana  is  characteristic  of 
the  upper  Mississippian,  we  find  in  the  Kinderhook  Acamhona  osar/ensis 
Swallow,  Hustedia  triangularis  Miller,  Eumetria  (f)  altirostris  White,  Retzia 
circularis  Miller,  R.  plicatn  Miller,  and  R.  popeana  Swallow,  all  Retzioids 
and  of  a  more  or  less  similar  type.  It  is  noteworthy  that  the  form  which 
I  have  referred  to  Eumetria  verneuiliana  is  confined  to  the  lower  beds  of 
the  Madison.  It  may  really  be  one  of  the  species  just  mentioned,  but  in 
its  present  condition  can  not  be  distinguished  from  the  better-known  form 
with  which  I  have  identified  it.  Camarophoria  rinfjens  was  described  frOm 
the  Burlington  chert  of  Missouri,  but  the  form  which  I  have  called  by  that 
name  is  present  in  the  Kinderhook  fauna  as  well. 


492     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

No  one  familiar  with  the  jjassage  beds  between  the  Devonian  and 
and  the  Carboniferous  would  hesitate  to  refer  even  the  basal  portion  of  the 
Madison  limestone  to  the  latter.  Yet  the  fauna  of  the  iMadison,  and  espe- 
cially, perhaps,  that  of  the  lower  portion,  is  not  without  Devonian  affinities. 
These  are  vested  chiefly  in  the  genera  Productella,  Aulopora,  and  Mich- 
elinia,  and  in  the  .species  Camarofwchia  sapplio  (?)  and  Spmfcr  suhattenuatus. 
Productella  alifern  n.  sp.,  it  will  be  noticed,  is  confined  to  the  lower  portion 
of  the  formation,  but  P.cooperensis,  a  highly  characteristic  Kinderhook  species, 
begiiming  in  the  lowest  bed  of  the  Madison  limestone,  survives  almost  to  its 
upper  limit.  .  Aulopora  geometrica  n.  sp.  is  found  at  only  one  locality  in  our 
collections,  which  occurs  a  little  below  the  middle  of  the  formation  (bed  26). 
MklieUnia  seems  to  be  restricted  in  its  occurrence  to  the  lowest  bed. 
CamarokecMa  sappho  (?)  also  is  found  toward  the  base,  in  bed  25,  while  S. 
suhattenuatus  has  not  been  located  in  any  bed  of  the  section  scheme. 

As  is  well  known,  C.  sappho  and  Sp.  suhattenuatus  occur  in  both 
Devonian  and  Carboniferous  deposits. 

The  following  conclusions  have  been  drawn  from  the  evidence  aff'orded 
by  the  table  of  distribution  of  species  given  on  page  484,  some  of  which 
has  already  been  dwelt  upon:  (1)  The  fauna  of  the  IVIadison  Hmestone 
can  be  referred  wholly  and  without  question  to  Carboniferous  time;  (2)  it 
has  a  marked  Kinderhook  facies;  (3)  it  is  essentially  the  same  fauna  as 
that  described  by  White,  by  Hall  and  Whitfield,  and  by  Meek,  and  by 
them  referred  to  the  Kinderhook  or  Waverly;  (4)  the  fauna  is  not  sep- 
arable into  independent  units,  but  must  be  regarded  as  a  whole. 

The  last  statement  should  perhaps  be  qualified  to  some  extent,  for  while 
a  large  percentage  of  types,  often  primitive  and  indicating  a  Kinderhook 
fauna,  are  persistent  almost  to  the  very  top,  at  the  same  time  there  are 
unquestionable  indications  of  advancing  development,  while  certain  admix- 
tures, sometimes  specific,  sometimes  generic,  indicate  an  age  much  later  than 
the  Kinderhook.  For  instance,  the  only  representatives  of  the  Devonian 
genera  Aulopora  and  Michelinia  are  confined  to  the  lower  portion  of  the 
Madison,  as  are  also  the  species  Leptcena  rJtomhoidalis,  Productella  cdifera  u. 
sp.,  Camarotcechia  sapplio  (f),  and  Sijrhu/othijris  carteri,  while  Endothyra  haUeyi 
var.  parva  n.  var.,  Derhya  l:eo1<uh  {!).  Archimedes  sp.,  and  Seminula  madison- 
ensis  n.  sp.  (of  the  type  of  S.  suhquadrata  and  S.  suhtdlta)  are  peculiar  to  the 
upper  portion.     At  the  same  time  it  will  not  be  amiss  to  recall  again  that  45 


LOWER  CARBONIFEROUS  FOSSILS.  493 

pel'  cent  of  tlio  fauna  of  tlie  lowest  third  of  the  Madison  persists  into  the 
upper  third,  many  of  the  species  being-  of  Kinderhook  age,  or  primitive  and 
allied  to  Kinderhook  species;  that  such  genera  as  Martinia  and  Seminula 
rang-e  from  the  very  botto)n  to  the  top  of  the  Madison;  and,  in  general,  the 
incom])leteness  of  much  of  the  data  tabulated,  by  reason  of  which  the  many 
species  known  at  j)resent  from  a  single  horizon,  and  giving  an  individual 
frtcies  to  ditierent  portions  of  the  series,  might  on  fuller  information  be 
found  to  have  a  more  extended  range.  A  complete  record  would  doubtless 
show  even  less  progressive  differentiation  in  the  series  than  now  appears. 

The  fact  that  Eumetria  vcrneifUiana  is  apparently  restricted  to  the 
lower  beds  remains  an  interesting  anomaly. 

I  do  not  believe  that  the  facts  warrant  an  exact  coiTelation  of  the 
Madison  limestone  with  the  Kinderhook  horizon  of  the  Mississippi  Basin, 
although  the  Kinderhook  affinities  of  its  fauna  are  obvious.  The  evidence 
of  such  genera  as  Endothyra,  Eumetria,  Archimedes,  and  other  forms 
already  mentioned,  can  not  be  set  aside,  and  the  probabilities  in^^olved  in 
placing-  the  Madison  limestone,  1,700  feet  thick,  to  offset  the  300  feet^  of 
shales,  sandstones,  and  limestones  of  the  Kinderhook  in  the  Mississippi 
Valley,  are  significant. 

A  more  probable  interpretation  of  the  facts  observed  seems  to  be  that 
the'  Madison  limestone  represents  a  large  portion,  possibly  even  the  whole, 
of  the  Lower  Carboniferous  period,  being-  a  Kinderhook  fauna  which 
through  uniformity  of  conditions  of  environment  had  maintained  its 
essential  characters  long-  after  its  contemporary  fauna  to  the  east  had  been 
superseded. 

This  would  presuppose  a  nearly  continental  distribution  of  the  Kinder- 
hook fauna  during  early  Mississippian  time,  which,  indeed,  we  have  some 

'  In  Missouri  tlie  Louisiana  limestoue  (Keyes,  1894,  Geol.  Surv.  Missouri,  Vol.  IV,  p.  51  et  seq.)  is 
said  to  havf  a  thickness  of  over  60  feet,  the  Hanuihal  shales  or  Vermicular  sanilstone  of  over  70  feet,  and 
the  Chouteau  limestone  of  nearly  100  feet,  making  a  maximum  thickness  of  230  feet.  The  same  author 
(loc.  cit.,  p.  46)  gives  a  section  at  Burliugtou,  Iowa,  in  which  the  Kinderhook  is  given  a  maximum  of  110 
feet  of  limestones,  sandstones,  and  shales.  Dana  (Manual  of  Geology,  4th  ed.,  1895,  pp.  637-639)  gives 
the  "Knohstone"  below  the  Keokuk  in  Indiana  a  niaximnm  thickness  of  500  feet.  In  Michigan  the 
Marshall  group,  the  equivalent  in  part  of  the  Kinderhook,  is  said  to  have  173  feet  of  grit  and  sandstones, 
the  overlying  Napoleon  group  having  123  feet  of  shale  and  sandstones.  In  Ohio  the  Waverly  group 
has  a  maximum  thickness  of  1,150  feet,  chiefly  shales  and  sandstones  (Orton,  Geol.  Snrv.  Ohio,  Vol.  VII, 
1893,  p.  4),  or,  as  is  averaged  in  the  same  table,  500  to  800  feet.  However,  Herrick  considers  a  portion 
of  this  to  be  of  Devonian  age,  while  the  rest  represents  the  Kinderhook,  Burlington,  and  Keokuk 
periods. 


494     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

evidence  for  believing-  to  have  been  the  case,  but  no  cataclasmic  interposi- 
tion of  barriers  is  necessary  to  account  for  the  individual  course  of  develop- 
ment which  the  fauna  seems  to  have  pursued  in  the  Rocky  Mountain  region 
and  in  what  is  now  the  Mississippi  Valley. 

The  approximate  uniformity  of  the  Madison  limestone  is  evidence  of  a 
protracted  period  of  quiet  and  uniform  physical  conditions,  while  the  rapid 
alternation  of  sediments  in  the  typical  J\lississippian  would  seem  to  indicate 
frequent  and  important  changes  in  environment  which  find  equal  expression 
in  the  varied  faunas  that  have  resulted.  The  wide  separation  of  the  two 
regions  geographically  would  readily  permit  of  theii'  independent  develop- 
ment, both  faunally  and  physiographically. 

Still,  the  conclusion  is  not  warranted  that  the  Madison  limestone  repre- 
sents the  entire  period  of  Mississippian  deposition.  In  Montana,  at  "Old 
Baldy,"  near  Virginia  City,  Meek  has  reported  fossils  of  the  Chester  group, 
with  a  probability  of  the  lower  formations  being  present;  and  from  near 
Fort  Hall,  between  Ross  Fork  and  Lincoln  Valley,  in  Idaho,  the  same 
authority  has  identified  many  species  characteristic  of  the  oolitic  beds  of 
the  St.  Louis  group  at  Spergen  Hill,  Indiana.^ 

These  localities  are  both  comparatively  near  the  Yellowstone  National 
Park  region,  and  it  is  hard  to  believe  that  if  the  ]\Iadison  limestone  was 
contemporaneous  in  part  with  either  of  these  periods  the  fauna  should  not 
clearly  indicate  it.  Indeed,  Meek,  commenting  upon  certain  collections 
made  at  various  localities  in  Montana  not  far  from  the  Yellowstone  Park, 
and  from  a  horizon  which  I  believe  to  be  equivalent  to  the  Madison  lime- 
stone (see  ante,  p.  487),  makes  the  following  statement:  "At  the  same  time 
that  I  would  refer  the  beds  from  which  these  fossils  were  obtained  to  the 
Carbcmiferous,  it  should  be  remarked  that  we  have  every  reason  to  believe 
that  they  belong  to  a  lower  horizon  in  the  series  than  those  from  which 
nearly  all  the  collections  from  'Old  Baldy'  Mountain  were  obtained;  also, 
than  the  fossiliferous  beds  on  the  divide  between  Ross  Fork  and  Lincoln 
Valley,  Montana."     (Loc.  cit.,  p.  433.) 

"We  may  therefore  conclude  that  tlie  j\Iadison  limestone  does  not  proba- 
bly represent  the  period  of  the  Genevieve  group,  but,  while  showing  distinct 
affinities  with  the  Kinderhook,  may  have  persisted  through  the  period  of 
the  Osage  group  as  well. 


'  Hayden,  Sixth  Ann.  Kept.  U.  S.  Geol.  Surv.  Territories,  etc.,  for  1872,  1873,  pp.  433,  434. 


LOWER  CARBONIFEROUS  FOSSILS. 


495 


The  fact  that  tlie  entire  Coal  Measure  series  is  lacking  in  this  region, 
or,  if  represented  at  all,  finds  expression  in  the  unfossiliferous  Quadrant 
quartzite,  makes  it  probable  that  the  same  forces  which  resulted  in  the  non- 
deposition  or  remoA'al  of  the  overlying  formation  affected  the  later  portion 
of  the  Lower  Carboniferous  time  in  the  same  way. 

Tabic  sliowing  the  representation  of  zoological  groups  in  the  Madison  limestone  fauna. 


Protozoa , 

Sponges 

Co'leiiterata 

Criiioidea 

Bryozoa 

Brachiopoda  

Lamellibranchiata 

Gastropoda 

Tiilobita 


Total 
speciefl. 


10 

47 

2 

8 

2 


Identified 
speciea. 


43 
1 
1 
g 


New 
species. 


Waverly 
species. 


14 


29 
1 


It  will  be  seen  from  the  foregoing  table  that  an  unusually  large  per- 
centage of  the  fauna  of  the  Madison  limestone,  not  only  in  the  number  of 
specific  types,  but  in  the  abundance  in  which  they  are  found,  consists  of 
brachiopods.  Most  conspicuous  for  their  rarity  are  the  lamellibranchs, 
of  which  only  two  specimens,  representing  two  different  species,^  have 
been  collected.  This  is,  perhaps,  explained  by  the  consideration  that  the 
Madison  limestone  is  usually  rather  pure  in  composition,  no  true  shales 
occurring  interbedded  with  it.  On  the  other  hand,  crinoids,  which  we 
might  expect  to  find  abundantly  in  such  extensive  calcareous  deposits,  are 
also  comparatively  rare.  Other  organic  types  appear,  perhaps,  in  not  far 
from  the  average  proportion. 

Two  localities  are  interesting  as  presenting  a  local  or  jjerhaps  more 
than  local  development  of  the  Madison  limestone  fauna.  One,  the  cherty 
limestone  of  Crowfoot  Ridge,  Gallatin  Range,  forms  the  upper  portion  of 
bed  24  of  the  section.  The  fauna  consists  of  Productus  semireflculatus,  Meno- 
lihyUmn  (f)  excavatum,  Naticopsis  (f)  sp.,  Platyceras  form  a,  CUothyris  roissyi, 
C.  crassicardinalis,  Spirifer  striatus  var.  madisonensis  n.  vai\,  Spirifer  centronatus, 

'  One  of  these,  very  fragmentary  (but  perhaps  referable  to  Ciipricardinia  consimilis  Hall  or  C. 
scitula  Herrick),  is  not  mentioned  in  the  report  following. 


4i>6  GEOLOCiY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Sjiiriferina  solidirostris,  Liorliynclms  haguei  n.  sp.,  Cnmarotoechia  metallica, 
ProdncteUa  cnopcrcnsis,  Chonefes  ornaUis,  Orthothetes  injiatus,  Crania  Jcevis, 
rtilopora  sp.,  Fe)ie,st€Ua  sp.  Of  these  L.  haguei,  Naticopsis  (f)  sp.,  Plati/ceras 
sp..  Crania  Icevis,  Ptilopora  sp.,  and  Fmestella  sp.  have  not  been  identified 
elsewhere  in  the  Madison  limestone,  with  whose  fauna,  however,  that  of 
these  localities  is  very  closel}'  related. 

The  red  beds  exposed  at  the  head  of  Conant  Creek,  Teton  Rang-e,  may 
also  be  separated  frcim  the  ]\Iadison  limestone,  with  which  lithologically  as 
well  as  famially  they  are  slightly  connected.  The  matrix  is  a  red  cal- 
careous shale,  more  shalj-  than  is  common  in  the  Madison  limestone,  in 
which  the  fossils  are,  as  a  rule.  Aery  Ijadly  crushed.  The  fauna,  which 
is  scantil}-  known  and,  on  account  of  the  condition  of  the  material, 
inadequatel)'  identified,  consists  of  Semimda  madisonensis  n.  sp.,  Spirifer 
■marioneniiis  (?),  Orthothetes  sp.,  and  Eridopora  (/)  sp.  None  of  these  is 
unquestionably  identical  with  species  found  in  beds  below,  thougli  they  are 
perhaps  cjuestionably  distinct.  This  locality  is  jDrovisionallj"  referred  to 
bed  32,  the  highest  in  the  formation.  More  evidence  may  show  it  to  be 
later  than  the  Waverly- 

DESCRIPTIONS  OF  SPECIES. 

DEVONIAN. 
C(ELEXTERATA. 

ACTINOSTROMA  Nicholson,  1886. 

ACTINOSTROMA  SJl. 

At  least  one  species  of  Stromatoporoid  is  represented  in  this  collection ; 
but  the  material,  badly  weathered  and  poorly  silicified,  scarcely  affords  the 
pronnse  of  more  than  a  generic  identification.  Therefore  it  has  not  been 
studied  by  means  of  microscopic  sections.  A  careful  examination  shows  a 
larffe  concentricallv  laminate  coenosteum.  The  laminae  are  moi'e  or  less 
contorted,  and  the  division  into  latilamiuse  is  not  apparent.  The  very  fine 
laminae  are  connected  by  minute  radial  pillars,  which  on  favorably  exposed 
surfaces  are  seen  to  be  continuous.  This  is  the  well-known  characteristic 
structure  of  the  genus  Actinostroma,  very  al^undant  in  Devonian  strata  in 
both  hemispheres. 


DEVONIAN  FoasiLS.  497 

Formation  and  locality:  Three  Forks  limestone,  near  the  divide 
between  Gallatin  Valley  and  Panther  Creek,  Bighorn  Pass,  Gallatin 
Kange,  bed  21 ;  S.  L.  Penfield.  East  slope  of  Antler  Peak,  Gallatin  Range; 
A.  C.  Gill.     South  slope  of  Antler  Peak,  Gallatin  Range;  J.  P.  Iddings. 

PACHYPHYLLUM  Edwards  and  Haime,  1850. 

Pachyphyllum  sp. 

Corallum  attaining  large  size  (the  present  specimen  measures  150  mm. 
in  longest  diameter  and  is  fragmentary).  Corallites  small  (9  to  10  mm. 
in  diameter),  separated  by  mural  zones  of  about  2.5  mm.  Septa,  32  to  34 
in  number,  and  alternating  in  size. 

The  specimen  studied  is  a  massive  weather-worn  fragment,  which  does 
not  show  the  external  surface  of  the  corallum,  nor  the  nature  of  the  calyces. 
The  rock  has  also  suffered  considei'ably  from  compression,  for,  though  the 
limestone  is  scarcely  altered,  the  corallites  are  flattened  and  the  lines  of 
the  septa  and  spongy  exothecal  and  dissepimental  tissue  often  broken  and 
discontinvious.  The  corallites  vary  much  in  size,  owing  probably  to 
difference  in  age,  but  are  more  uniform  where  the  corallum  is  crowded. 
The  average  of  mature  cells  is,  perhaps,  as  above  stated.  That  measure- 
ment, however,  relates  to  the  septate  portion  only.  The  mural  tissue  is 
very  finely  vesicular  and  is  not  penetrated  by  the  septa,  which  are  about  34 
in  number.  They  are  strong,  but  have  not  the  Acervularia-like  expansion 
so  strongly  developed  as  in  P.  devoniense.  Longitudinal  sections  show  alter- 
nating stripes  of  finely  vesicular  mural  tissue  and  the  longitudinally  banded 
septate  portion.  This  is  occupied  by  dissepimental  plates,  but  the  presence 
of  complete  tabulse  has  not  been  ascertained. 

While  I  am  convinced  that  this  species  is  as  yet  undescribed,  and 
although  the  characters  established  are  sufficient  to  enable  one  to  distinguish 
it  from  any  forms  known  and  to  recognize  it  again  at  the  type  or  adjacent 
localities,  yet  I  have  not  felt  justified  in  proposing  for  it  a  new  name,  since  the 
material  is  scarcely  suitable  for  illustration;  and  it  is  not  improbable  that 
from  other  stations,  more  or  less  remote,  new  types  will  subsequently  be 
described,  which  it  will  not  be  possible  to  separate  from  this,  owing  to  the 
imperfections  of  the  latter. 

The  only  species  which,  so  far  as  I  am  aware,  have  been  referred  to 

MON  XXXII,  PT  II 32 


498  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

this  genus  in  this  country  are  the  three  mentioned  by  Miller  in  his  North 
American  Geology  and  Paleontology,  viz:  P.  devoniense,  P.  woodmani,  and 
P.  solitarium.  The  last  mentioned  of  these  can  scarcely  be  referred  to  the 
genus  Pachyphyllum,  since  it  is  described  as  a  simple  coral  with  an  epitheca 
(or  theca)  and  without  exothecal  tissue.  PachjplujUum  tvoodmani  was 
originally  mentioned  by  White  as  Smithia  tvoodmani}  Hall  and  Whitfield 
describe  and  figure  it  -  under  the  name  of  PachjphjUum  tvoodmani,  saying 
"the  exsert  form  of  the  cells,  and  their  limitation  by  an  outer  wall,  are 
features  which  do  not  exist  in  Smithia,  but  pertain  to  the  genus  Pachyph}^- 
lum."  In  point  of  fact,  Pachyphyllum  seems  to  be  a  synonym  of  Smithia. 
The  genus  is  characterized  by  Edwards  and  Haime  as  follows:  "Corallum 
compound,  increasing  by  lateral  gemmation.  Corallites  not  separated  by 
an  individual  epitheca,  but  united  in  their  lower  portion  by  a  large  develop- 
ment of  costJB  and  exothecal  tissue;  septa  and  tabulfe  well  developed. 
Pachyphyllum  is  distinguished  from  all  othei'  Cyathophylloids  by  the 
development  of  the  costaj  and  exothecal  tissue.'"  The  descrijDtion  of 
P.  houchardl,  the  type  (ibid.),  accords  with  the  generic  description,  but, 
unfortunately,  by  some  oversight,  it  was  not  figured  by  the  authors. 
Although  there  is  the  usual  reference  heading  the  specific  description,  there 
is  no  corresponding  plate  or  description  of  plate  in  the  accompanying  atlas. 
I  am  not  aware  that  it  has  subsequently  been  figured.  Smithia  is  described 
by  the  same  authors  in  the  following  terms:  "Corallum  compound,  astrei- 
form,  multiplying  by  submarginal  gemmation.  Corallites  intimately 
connected,  having  the  same  structure  as  Acervularia  (i.  e.,  with  two  walls; 
septocostal  structure  well  developed  between  the  walls;  much  less  in  the 
central  area.  No  columella.  Tabular  little  developed),  except  that  they 
lack  external  walls  and  that  the  septocostal  rays  are  more  or  less  confluent. 
No  columella."     (Loc  cit.,  p.  142.) 

A  comparison  of  the  two  genera  shows  that  they  are  at  least  very 
closely  related.  One  great  distinction,  implied  rather  than  expressed,  is 
that  in  Smithia  the  one  wall  is  regarded  as  homologous  with  the  inner 
wall  of  Acervularia,  the  intercellular  tissue  being  then  simply  confluent 
intermural  tissue  of  adjacent  cells.     In  Pachyphyllum,  on  the  other  hand, 

1  Geol.  Kept.  Iowa,  1870,  Vol.  I,  p.  188. 

2  Twenty -third  Ann.  Kept.  New  York  State  Cab.  Nat.  Hist.,  p.  231,  PI.  IX,  fig.  9. 

3  Hist.  NAt.  des  Coralllaires,  Vol.  Ill,  Paris,  1857,  p.  391. 


DEVOVIAN  FOSSILS.  499 

the  imperfect  wall  is  regarded  as  equivalent  to  the  theca  of  most  rugose 
corals,  the  outer  wall  of  Acervularia,  while  the  surrounding  tissue  is 
exothecal  in  nature,  a  sort  of  cocnenchyma.  If  this  distinction  can  be 
established,  the  two  genera  would  be  widely  different  in  fact,  however  diffi- 
cult it  would  be  to  distinguish  them  in  practice.  However,  there  seems  to 
be  little  if  any  reason  why  the  single,  imperfect  central  walls  in  both  genera 
should  not  be  homologous  with  each  other  and  with  the  imperfect  inner 
wall  of  Acervularia.  Thus  the  two  differentiating  characters  mentioned  by 
Hall  and  Whitfield  fall  to  tlie  gi-ound,  for  in  neither  genus  are  the  corallites 
limited  by  an  outer  wall.  As  to  the  exsert  form  of  the  cells,  this  character 
is  not  mentioned  in  the  generic  description  of  Pachyphyllum,  but  P. 
bouchanli  is  described  with  "Walls  strong  and  distinct;  calyces  circular, 
deep,  with  edges  rather  elevated."  This  character,  then,  is  not  regarded  as 
of  generic  value,  and  in  the  type  species  is  not  especially  striking.  The 
chief  points  of  distinction  which  can  be  drawn  from  Edwards  and  Haime's 
description  (leaving  out  their  view  of  the  homologies  of  the  inner  wall, 
which  I  hold  to  be  questionable)  come  to  this,  that  Pachyphyllum  -has 
very  extended  tabulse,  while  Smithia  has  them  only  slightly  developed,  a 
character  which,  taken  alone,  is  of  doubtful  generic  importance. 

Smithia  is  generally  regarded  as  a  synonym  for  Phillipsastrsea,  but 
Edwards  and  Haime  claim  that  it  is  distinguished  from  the  latter  by  the 
presence  of  a  columella.  If  constant,  this  would  seem  to  be  a  good 
character.  After  studying  the  type  species,  Nicholson  states  that  Phillips- 
astrsea (=  Smithia)  has  essentially  the  structure  of  Heliophyllum — i.  e.,  with 
carinate  septa,  fossula,  and  without  an  inner  wall.  If  Smithia  is  indeed 
synonymous  Avitli  Phillipsastrsea,  then  Pachyphyllum  is  a  quite  different 
thing.  But  if  Smithia  and  Pachyphyllum  are  as  Edwards  and  Haime  have 
described  them,  it  seems  probable  that  the  latter  is  a  synonym  of  the 
former. 

It  is  possible  that  three  types  are  included  among  the  five  species 
referred  to  Pachyphyllum.  One  of  these,  P,  soUtarium,  I  think,  beyond 
a  doubt,  must  be  placed  elsewhere.  Or,  is  it  perhaps  the  initial  cell 
of  a  Pachyphyllum  colony?  Another  type  which  is  structurally  near 
Smithia  is  that  represented  by  P.  houchardi  and  P.  woodniani.  A  third 
type   is  found   in  P.  devoniense   and   the   form   above   described.     It   is 


500  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

characterized  by  a  mural  zone  of  vesicular  tissue,  which  is  not  penetrated 
by  the  septa.  Edwards  and  Haime  say  that  in  P.  devoniense  this  zone  is 
traversed  by  the  costaj,  which  are  not  very  pronounced,  but  distinct.  This 
is  scarcely  apparent  in  the  figure,  but,  if  so,  the  form  represents  an  inter- 
mediate stage  between  P.  houchardi  and  Pachyphylliim  sp.,  where  the  thick 
costse  terminate  in  the  mural  zone  without  penetrating  it. 

Formation  and  locality:  Three  Forks  limestone,  north  side  of  saddle 
west  of  Mount  Miller,  Absaroka  Range ;  Louis  V.  Pirsson. 

CYATHOPHYLLUM  Goldfuss,  1826. 

Cyathophyllum  c^spitosum  Goldfuss  (f) 
CyaihophyUum  ccmpitosum  Goldfuss,  1826.     Petrefacta  Germanic,  p.  60. 

In  the  calcareous  sandstone,  associated  with  specimens  of  Actiuostroma, 
Pachyphyllum,  Atrypa,  etc.,  is  a  species  of  Cyathophyllum,  which  may  be 
identical  with  G.  ccespltosum  Goldf  It  consists  of  isolated  fragments  of 
cylindrical  corallites,  which  have  about  forty  alternately  long  and  short 
septa,  a  tabulate  central  portion,  and  a  vesicular  outer  zone.  In  size,  general 
character,  and  in  specific  detail,  as  far  as  determinable,  these  strongly 
resemble  Goldfuss's  species,  and  may,  like  it,  when  entire,  have  grown  in 
tuftlike  masses.  Indeed,  the  small  diameter  and  the  cylindrical  form 
of  the  corallites  are  favorable  to  such  an  interpretation.  C.  ccespitosum  is 
already  known  to  occur  in  American  strata,  being  found  in  Upper  Helder- 

berg  rocks. 

Formation  and  locality:  Three  Forks  limestone,  near  the  divide  between 
Gallatin  Valley  and  Panther  Creek;  Bighorn  Pass,  Gallatin  Range,  bed  21; 
S.  L.  Penfield.  East  slope  of  Antler  Peak,  Gallatin  Range;  H.  C.  Gill. 
North  side  of  saddle  west  of  Mount  Miller,  Absaroka  Range;  Louis  V. 
Pirsson. 

CLADOPORA  Hall,   1852. 

Cladopora  sp. 

Like  the  other  corals  from  the  same  bed,  specimens  ot  Cladopora  are 
coarsely  silicified  and  considerably  weathered.  The  branches  are  circular, 
and  about  5  mm.  in  diameter.  The  pores  are  nearly  circular,  small  (about 
0.25  mm.  in  diameter),  and  separated  from  each  other  by  a  distance  about 


DEVONIAN  FOSSILS.  501 

equal  to  their  own  diameter.  What  the  shape  of  the  orifice  may  have  been 
originally  it  is  impossible  now  to  determine.  In  its  present  condition  the 
con-allum  resembles  C.  lahiosa  and  C.  inngms,  both  of  Romiuger/  but  more 
especially  the  form  figured  as  a  variety  of  C.  lahiosa} 

The  form  under  discussion  resembles  C.  lahiosa  in  the  slendeniess  of 
the  stem,  but  the  pores  are  more  distant,  and  at  present  not  labiate.  It 
resembles  C.  pinfjuis  in  the  thick  interstitial  tissue  between  the  cells  and 
in  the  less  labiate  condition  of  the  latter ;  but  the  branches  are  less  robust 
and  the  cell  apertures  a])j)arently  smaller. 

Formation  and  locality:  Three  Forks  limestone,  near  the  divide 
between  Gallatin  Valley  and  Panther  Creek,  Bighorn  Pass,  Grallatin  Range, 
bed  21;  S.  L.  Penfield. 

FAVOSITES  Lamarck,  1812. 

Favosites  sp. 

PI.  LXVI,  fig.  8rt. 

Corallum  rather  small,  about  50  mm.  (I)  in  diameter;  cells  small,  very 
closely  tabulate,  tabulae  being  about  0.5  mm.  apart.  Number  of  rows  of 
mural  pores,  character  of  the  same,  and  nature  of  the  epitheca,  not  known. 

The  material  submitted  was  not  found  in  place.  It  consists  of  a  frag- 
mentary silicified  example,  which,  while  showing  some  characters  very 
plainly  (e.  g.,  the  tabulation),  has  others  obliterated  so  that  specific  identi- 
fication of  the  form  is  impossible.  It  can,  however,  be  affirmed  that  it  does 
not  belong  to  any  Carboniferous  representative  of  the  genus,  at  least  such 
as  are  yet  described,  and  it  can  therefore  with  great  probability  be  regarded 
as  belonging  to  Devonian  or  Upper  Silurian  time. 

Formation  and  locality :  Three  Forks  limestone,  north  side  of  Soda 
Butte  Creek,  Absaroka  Range;  J.  P.  Iddings. 

'Geol.  Surv.  Michigan,  Vol.  Ill,  PL  II,  1876,  pp.  52-53,  PI.  XXI,  figs.  2,  3. 
'^  Loc.  cit.,  fig.  3,  lowest  specimen. 


502  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

BRACHIOPODA. 

ATRYPA  Dalmau,  1827. 
Atrypa  reticularis  Linud. 

PI.  LXVI,  flgs.  la,  lb,  If. 

Atrypa  reticularis  Linac^,  1767 :  Systema  Naturse,  ed.  xii,  Vol.  I,  p.  1132.  Hall,  1852 :  Pal. 
New  York,  Vol.  II,  p.  72,  PL  XXIII,  figs.  8,  Sa-8»;  p.  270,  PI.  LV,  flgs.  5a-5u. 
Billiugs,  1863:  Logan,  Geol.  Surv.  Canada,  Eept.  Progress  1843-1863,  p.  318, 
figs.  335a-335c;  p.  384,  figs.  4160-4160.  Hall,  1867 :  Pal.  New  York,  Vol.  IV,  p. 
316,  PL  Lll,  flgs.  1-3,  7-12;  PL  LllI,  flgs.  3-19;  PL  LIIlA,  flgs.  22,  23.  Meek 
and  Wortheu,  1868:  GeoL  Surv.  Illiuois,  VoL  III,  p.  432,  PL  XIII,  flg.  11. 
Meek,  1877:  King's  U.  S.  GeoL  Expl.  40tli  Par.,  VoL  IV,  p.  38,  PL  I,  figs.  7,  7a; 
PL  III,  flg.  6.  White,  1880:  Second  Ann.  Kept.  Indiana  Bureau  Statistics  and 
Geology,  p.  502,  PL  V,  flgs.  7,  8,  9,  Walcott,  1884 :  Mon.  U.  S.  GeoL  Surv.,  Vol. 
VIII,  p.  150,  PL  XIV,  figs.  6,  6a,  6b.  Beecber  and  Clarke,  1889:  Mem.  New 
York  State  Mus.  Nat.  Hist.,  p.  51,  PL  IV,  figs.  12-20.  Hall  and  Clarke,  1893: 
Pal.  New  York,  VoL  VIII,  Pt.  II,  p.  165,  fig.  153;  PL  LV,  figs.  1-17.  Herrick, 
1895:  GeoL  Oliio,  Vol.  VII,  PL  XX,  fig.  7. 

This  well-kuowu  and  uuiversally  distributed  form  needs  no  further 
description.  It  has  as  yet  been  identified  from  but  one  locaUty  in  the 
Yellowstone  National  Park,  is  represented  entirely  by  casts,  and  is  a  small, 
coarsely  plicate  form,  similar  to  that  from  the  Lockport  (often  called  Niag- 
ai-a)  Hmestone,  and  identified  by  Walcott  fi'om  Upper  Devonian  strata. 

Formation  and  locality:  Three  Forks  limestone,  base  of  bluff,  Little 
Sunlight  Creek;  Arnold  Hague.     Silurian  and   Devonian  throughout  the 

world. 

Atrypa  missouriensis  Miller. 

PL  LXVI,  figs.  2a,  2b,  2c. 

Atrypa  reticularis  (var.)  Meek,  1877:  King's  U.  S.  GeoL  Expl.  40tli  Par.,  VoL  IV, 

p.  38,  PL  III,  fig.  6a. 
Atrypa  desquamata  V/alcott  (uou  Sowerby),  1884:  Mou.  U.  S.  GeoL  Surv.,  Vol.  VIII, 

p.  150,  PL  XIV,  figs.  4,  4a. 
Atrypa  missouriensis  Miller,  1894:  Eigbteeuth  Ann.  Kept.  State  Geologist  of  Indiana, 

1893,  p.  315,  PI.  IX,  flgs.  19-21. 

Shell  rather  small,  subcircular,  variable  in  shape.  Dorsal  and  ventral 
valves  moderately  and  equally  convex,  finely  striate,  not  at  all  or  only 
obscurely  marked  by  distant  concentric  striae,  which,  moreover,  are  not 


DEVONIAN  FOSSILS.  503 

sqiianiose.  Beak  of  the  veutial  valve  small,  not  much  incurved;  area  small. 
Anterior  margin  distinctly  but  not  strongly  sinuate. 

There  can  be  little  (U>ubt  that  this  is  the  same  form  for  which  Miller 
proposed  the  name  Atnjpa  inissouriensis,  and  which  had  been  previously 
referred  to  by  Meek  as  Atrypa  reticularis  and  by  Walcott  as  Atrypa  desqua- 
muUi  (loc.  cit). 

A.  missoiiriensis  is  described  from  Middle  Devonian  rocks  (probably 
Hamilton  age),  and  the  type  locality  is  3  miles  from  Otterville  and  17 
miles  west  of  Sedalia,  Missouri.  A  form,  probably  referable  to  Miller's 
species,  is  found  at  Fulton,  Missouri,  in  rocks  of  Hamilton  age,  and  with 
this  the  material  from  the  Yellowstone  National  Park  is  very  closely 
allied,  perhaps  specifically  identical.  It  is  possible  that  the  finely  striated 
variety  of  A.  reticularis,  mentioned  by  Walcott^  and  said  to  resemble  a 
variety  fi-om  the  Hamilton  and  Chemung  groups  in  Iowa,  may  also  be 
placed  in  the  list  of  synonyms. 

^i.  missouriensis  occurs  in  considerable  abundance  at  several  localities 
in  the  Yellowstone  Park,  but  it  is  rarely  found  associated  with  Atrypa 
reticularis,  which  is  known  from  the  same  region.  The  two  forms  are  thus 
distinct  in  distribution  as  well  as  intrinsic  character,  when  this  region 
alone  is  contemplated,  and  the  natural  tendency  is  to  refer  them  to 
diff'erent  species,  but  in  view  of  the  almost  universal  distribution  of  A. 
reticularis,  and  its  equally  extensive  range  of  ^'ariation,  perhaps  a  varietal 
distinction  is  all  that  is  warranted.  Only  a  monographer  will  be  com- 
petent to  determine  specific  limitations  in  this  protean  type. 

A.  desquamata  in  this  country  is  nothing  more  than  A.  reticularis 
with  an  erect  beak,  area,  and  unconcealed  foramen ;  and  the  same  appears 
to  be  equally  true  of  the  European  forms.  This  character  or  group  of 
characters  seems  scarcely  of  specific  value,  but  in  any  case  the  same 
peculiarities  of  surface,  etc.,  which  distinguish  A.  missouriensis  from  A. 
reticularis  serve  to  diff'erentiate  it  from  A.  desquamata  also.  Although  it 
is  a  mature  form,  A.  missouriensis  is  characterized  by  neologic  traits,  and 
agrees  very  closely  with  young  examples  of  A.  desquamata  as  figured  by 
Davidson."  Still,  full-grown  shells  are  the  only  ones  with  which  we  are 
justified  in  comparing  it. 


'Mod.  U.  S.  Geol.  Surv.,  Vol.  VIII,  1884,  p.  150. 

"British  Fossil  Brachiopoda,  Vol.  Ill,  Part  VI,  PI.  XI,  tigs.  6, 6o. 


504  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Formation  and  locality :  Three  Forks  limestone,  south  slope  of  Antler 
Peak,  Gallatin  Range ;  south  side  Soda  Butte  Creek,  northwest  of  Abiathar 
Peak,  Absaroka  Range;  J.  P.  Iddings.  North  side  of  saddle  west  of  Mount 
Miller,  Absaroka  Range;  Louis  V.  Pirsson.  Near  Otterville  and  Sedalia, 
Missoui-i. 

SPIRIFER  Sowerby,  1815. 

Spirifer  engelmanni  Meek. 
PL  LXVI,  figs,  :^a,  3b,  Sc,  3d. 

Spirifera  engelmanni  Meek,  1860:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  308.  Meek,  1877: 
King's  U.  S.  Geol.  Espl.  40tli  Par.,  VoL  IV,  p.  41,  PI.  Ill,  figs.  3-3a. 

Spirifer  engelmanni  Meek,  1876:  Simpson's  Rept.  Expl.  Gt.  Basin.  Terr.  Utah,  p.  316, 
PI.  I,  figs.  Irt-lc. 

There  is  only  one  example  of  this  species.  Though  otherwise  appar- 
ently identical  with  the  smaller  forms  of  S.  engelmanni,  it  is  abnormal  in  this, 
that  the  strong  plication  bounding  the  sinus  bifurcates,  the  two  inner  ribs 
lying  upon  the  sides  of  the  sinus.  1  have  not  observed  this  in  S.  encielmanni 
from  Nevada,  but  have  seen  dorsal  valves  with  a  shallow  median  sulcus  on 
the  fold,  so  that  there  is  little  reason  for  believing  that  such  irregularities 
do  not  occur  on  the  other  valve  as  well.  The  specimen  could  scarcely  be 
a  young  individual  of  S.  disjunotm,  for  that  species  has  finer  plications, 
which  are  distributed  in  large  numbers  on  both  fold  and  sinus. 

Formation  and  locality:  Three  Forks  limestone,  south  side  Soda  Butte 
Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings.  Middle 
Devonian,  Neils  Valley,  Utah;  White  Pine  District,  Nevada. 

ATHYRIS  McCoy,  1844. 

Athyris  vittata  var.  triplicata  n.  var. 
PI.  LXYI,  figs,  la,  4&,  4c. 

Shell  small,  subcircular.  The  two  valves  moderately  and  equally 
convex.  Ventral  valve  marked  by  a  broad,  shallow  median  sinus.  On 
either  side  is  a  faint  sinuation  separated  from  the  median  one  by  a  sharp 
ridge.  Dorsal  with  well-defined,  square  fold,  bounded  on  either  side  by  an 
angular  depression,  after  which  follow,  one  on  each  side,  two  other  slight 
folds.  All  the  plications  of  this  shell  are  discernible  for  only  a  short 
distance  back  from  the  margin.     Width,  9  nun. ;  length,  nearly  the  same. 


DEVONIAN  FOSSILS.  505 

The  shell  is  so  badly  exfoliated  that  its  surface  characters  are  unknown, 
and  the  generic  reference,  as  a  whole,  is  donbtful.  It  resembles  Athyris 
ritfnfa  of  the  Corniferoiis  and  Hamilton  groups,  and  A.  nngelica  of  the 
Hamilton,  some  examples  of  which  approach  this  shell,  though  not  very 
closely.  It  finds  a  close  ally  in  A.  (OHjclira  var.  occidentalis  Whiteaves 
(Cont^  Canadian  Pal.,  Vol.  I,  Pt.  HI,  1891,  p  227,  PI.  XXXII,  figs.  3-3a), 
from  which  it  differs  chiefly  in  having  an  additional  low  fold  on  either  side. 
The  two  forms  resemble  each  other  more  than  either  A.  anffeUca  or  A. 
vittnta.  Whiteaves's  shell  is  probably  worthy  of  specific  distinction,  and  the 
relation  between  it  and  the  form  from  the  Madison  limestone  would  be  best 
expressed  by  making  the  latter  a  variet}'  of  the  former.  The  name  of  my 
shell  would  then  be  Athyris  occidentalis  var.  triplicata. 

Formation  and  locality :  Three  Forks  limestone,  south  side  of  Soda 
Butte  Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddiugs. 

GASTROPODA. 

PLEUROTOMARIA  Defrance,  1824. 

Pleurotomaria  ISAACS!  Hall  and  Whitfield.  (!) 

PI.  LXVI,  figs.  5a,  56. 

Pleurotomaria  isaacsii  Hall  and  Whitfield,  1873 :  Tweuty-third  Kept.  New  York  State 
Cab.  Nat.  Hist.,  p.  238,  PL  XII,  figs.  6,  7. 

The  form  which  I  have  referred  to  Hall  and  Whitfield's  species  occurs 
as  an  isolated  specimen  of  a  large  gastropod  shell.  As  far  as  the  somewhat 
imperfect  condition  of  the  material  permits  a  comparison,  the  specimen  from 
Yellowstone  National  Park  is  very  close  to  P.  isaacsi.  It  is  a  large  flattened 
shell,  about  59  mm.  in  diameter,  agreeing  in  size,  general  proportion,  and 
peritreme  section  with  the  species  to  which  I  have  referred  it.  On  the 
other  hand,  the  spire  is  a  little  more  elevated  than  the  specimen  figured  by 
Hall  and  Whitfield,  the  whorls  a  little  more  angular  in  section,  with  the 
upper  surface  obliquel)^  plane  or  slightly  concave.  The  shell  appears  to  be 
without  ornamentation. 

Pleurotomaria  isaacsi  is  from  the  Lower  Devonian,  probably  the  Scho- 
harie grit. 

Formation  and  locality:  Three  Forks  limestone.  Wall  Canyon,  Clark 
Fork  Valley;  Arnold  Hague.  Lower  Devonian,  near  Raymond  Station, 
Iowa. 


50(3     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Pleurotomaria(?)  sp. 

A  rather  large  gastropod  shell,  broken  and  embedded  m  limestone. 
Height,  about  22.5  mm.;  diameter  at  base,  25  mm.;  whorls,  five  or  six. 
Umbilicus  extending  through  three  or  four  whorls.  Apparently  without 
ornamentation.  Cross  section  of  whorl  subquadrate,  the  upper  and  lower 
faces  converging  centripetally,  the  distal  and  proximal  faces  converging 
toward  the  apex.     Shell  thick,  interior  section  of  whorl  nearly  circular. 

The  matrix  inclosing  the  specimen  is  weatherworn  so  as  to  form  a 
transverse  section  somewhat  more  than  half  through  tlie  shell.  From  this 
the  above  notes  were  taken.  The  surface  as  reijresented  by  section  is 
unornamented,  for  the  line  representing  the  outer  face  is  simple  and  entire. 
Although  a  certain  identification  is  impossible,  this  fact  operates  against 
refeiTing  the  form  to  Pleurotomaria.  It  may  go  with  the  genus  Palseo- 
trochus,  but  is  distinct  from  anything  yet  referred  thereto. 

Formation  and  locality:  Three  Forks  limestone,  north  side  of  saddle 
west  of  Mount  Miller,  Absaroka  Range;  Louis  V.  Pirsson. 

LOXONEMA  Phillips,  1841. 

LOXONEMA   DELICATUM   n.  sp. 
PI.  LXVI,  fig.  6a. 

Shell  very  small,  elongate.  Spire  consisting  of  about  five  volutions; 
whorls  well  rounded  and  suture  line  depressed.     Aperture  nearly  circular. 

The  specimen  described  is  a  cast,  not  showing  any  surface  characters. 
It  is  foimd  associated  with  Platijstoma  minutum  and  other  gastropods  (see 
ante,  p.  482). 

Formation  and  locality:  Three  Forks  limestone,  south  side  of  Soda 
Butte  Creek,  northeast  of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings. 

PLAT Y  STOMA  Conrad,  1842. 

Platystoma  minutum  n.  sp. 
PI.  LXVI,  figs.  7(1,  Ih. 

Shell  extremely  small,  conical,  flattened.  Spire  low  and  consisting  of 
about  three  volutions.  Aperture  somewhat  oblique,  elongate,  elliptical. 
Surface  nearly  smooth,  ornamented,  if  at  all,  only  with  lines  of  growth. 


LOWER  CARBONIFEROUS  FOSSILS.  507 

This  species  occurs  at  the  south  side  of  Soda  Butte  Creek,  northeast 
of  Abiathar  Peak,  Absaroka  Range,  associated  with  Loxonema  delicatmn  and 
a  number  of  other  gastropod  forms  too  imperfect  for  description  (see 
ante,  p.  482). 

Formation  and  locaHty :  Three  Forks  Hmestone,  south  side  of  Soda 
Butte  Creek,  northeast  of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings. 

LOWER    CARBONIFEROUS. 
PROTOZOA. 

ENDOTHYRA  Philhps,  1845. 

Endothyra  baileyi  var.  parva  n.  var. 

PI.  LXXI,  flgs.  13rt,  Ub,  13c. 

This  form  is  known  only  by  microscopic  sections  and  therefore  very 
inadequately ;  but  the  correctness  of  the  reference  to  Endothyra  seems 
unquestionable,  and  I  am  even  in  doubt  whether  it  is  varietally  distinct 
from  Hall's  species.  So  far  as  my  observations  go,  it  is  never  much  over 
half  the  size  of  Endothyrahaileyi,'^  and  is  more  simple — i.  e.,  less  numerously 
chambered.  Although  these  characters  are  ordinarily  of  questionable  diag- 
nostic value,  appearing  as  it  does  in  quite  different  associations,  the  Western 
form  seems  worthy  to  be  classed  as  a  distinct  variety.  And  it  is  not  improb- 
able that  a  study  of  the  shell  under  auspices  more  favorable  than  by 
microscopic  sections  will  more  fully  justify  the  distinction.  This  form 
should  be  compared  with  E.  howmani  Phillips  and  E.  lobata  Brady,  which 
Brady '^  considers  to  be  the  same  as  E.  bailey i.  They  are  less  robust  and 
more  simple  forms. 

Formation  and  locality:  Madison  limestone.  White  Mountain,  Absaroka 
Range;    Arnold  Hague.      Amphitheater  east  of  Bannock   Peak,  Gallatin 
Range,  bed  30;  Snake  River  Valley,  west  of  Two  Ocean  Plateau;  W  H 
Weed. 


'  See  PI.  LXXI,  figs.  12a,  126. 

Si  PaliBontographical  Soc,  Vol.  XXX,  p.  92,  PI.  V,  figs.  1-4. 


508  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

PORIFERA. 

HOLASTERELLA  Carter,  1852. 

HOLASTEEELLA    WRIGHTI    var.  AMERICANA   11.  var. 
PI.  LXXI,  fig.  11a. 

The  only  trace  of  sponge  remains  which  has  been  observed  in  Yellow- 
stone National  Park  consists  of  two  or  three  delicate  silicified  spicules, 
which,  for  lack  of  a  better  designation,  I  have  called  by  the  above  name. 
While  closely  related  to  Carter's  species,^  I  think  it  is  undoubtedly  distinct. 
At  the  same  time,  in  view  of  the  limited  amount  of  material  at  my  disposal, 
I  do  not  feel  justified  in  proposing  a  new  specific  name,  Avhile  the  occurrence 
of  the  form  seemed  worthy  of  notice  and  a  name  of  some  sort  desirable. 

The  spicules  in  question  are  of  the  regular  hexactinellid  type.  The 
six  arms  are  stout  and  short,  each  quickly  subdividing  into  four  long 
tapei'ing  branches.  These  are  set  at  an  acute  angle  with  one  another,  and 
ornamented  with  fine  nodes,  which  tend  to  an  arrangement  in  transverse 
rows,  giving  the  branches  a  finely  annulated  appearance. 

The  genus  Holasterella,  so  far  as  I  am  aware,  is  restricted  in  its  range 
to  Lower  Carboniferous  strata;  and  this  is  the  first  notice  of  its  occuiTence 
in  this  country. 

Formation  and  locality:  Madison  limestone,  divide  between  Gallatin 
Valley  and  Panther  Creek,  near  Bighorn  Pass,  Gallatin  Range,  bed  24; 
Arnold  Hague. 

C(ELENTERATA. 

AULOPORA  Goldfuss,  1826. 

AULOPORA    GEOMETRICA   n.    Sp. 

PL  LXVII,  fig.  6a. 

Corallum  free  ("?),  spreading.  Coralhtes  small,  each  regularly  budding 
off  two  other  individuals,  which  diverge  at  an  angle  of  about  120°,  so  that 
the  colony  as  a  whole  presents  a  regular  network  with  hexagonal  openings. 
Length  of  corallites  about  5  imn.;  diameter,  from  1.25  to  1.5  mm 

1  See  Carter,  1880:  Ann.  Mag.  Nat.  Hist.,  Vol.  VI,  p.  209,  t.  14b,  figs.  1-17;  and  Hinde,  1883:  Cat. 
Foss.  Sponges,  Brit.  Mus.,  p.  153,  PI.  XXXII,  figs.  i-ig. 


LOWER  CAUBONIFEROI  a  FOSSILS.  509 

This  species  is  interesting  as  being  the  first  rejiresentative  of  the  genus 
Aiilopora  described  from  the  Carboniferons  rocks  of  this  country.  The 
form  in  question  presents  some  apparent  divergences  from  typical  Aulopora 
habit  and  stracture,  such  as,  if  they  could  be  established,  would  be  suffi- 
cient for  generic  differentiation.  However,  I  have  but  one  specimen  of  the 
species,  and  it  does  not  afford  conclusive  evidence  on  the  points  in  question. 
The  corallum  appears  to  have  been  free,  or  at  all  events  to  have  outrun  the 
surface  on  which  it  was  creeping,  and  the  unaunexed  portion  to  have  been 
broken  away;  for  there  is  no  evidence  of  attachment  in  its  present  condition. 
The  corallites  are  small  and  cut  up  internally  by  infundibuliform  dissepimental 
tissue,  somewhat  as  in  Syringopora.  At  least,  there  are  usually  to.  be  seen 
one  or  more  cylindrical  walls  internally  concentric  with  the  theca.  It  may 
be  thought,  and  perhaps  correctly,  that  this  is  the  initium  of  a  Syringoporoid 
colony.  As  against  this  view,  it  may  be  stated  that  no  such  colonies  are 
known  from  the  locality  in  question,  nor  would  the  hypothetical  colony 
restored  from  this  initium  probably  agree  specifically  with  any  yet 
discovered  in  the  Yellowstone  Park. 

Formation  and  locality:  Madison  limestone,  Bighorn  Pass,  Gallatin 
Range,  cherty  belt;  Arnold  Hague. 

SYRINGOPORA  Goldfuss,  1826. 

Syringopora  aculeata  n.  sp. 

PI.  LXVII,  figs.  5a,  56. 

Corallum  large,  never  favositiform ;  corallites  small,  radiating,  sepa- 
rated by  distances  varying  from  one-half  to  five  or  six  times  the  diameter 
of  the  average  corallite.     Usually  about  1  diameter  apart. 

Corallites  about  1.5  mm.  in  diameter.  Septa  represented  by  spines 
set  in  about  twenty-five  vertical  rows.  The  number  appears  to  be  varia- 
ble, and  can  not  be  stated  with  exactness.  The  spines  are  long  and  very 
numerous,  so  that  they  form  a  striking  feature  in  any  transverse  or  longitudi- 
nal section.  Dissepimental  structures  well  developed,  spinose,  vesiculose 
infundibuliform,  the  dissepimental  plates  converging  very  gradually. 

Formation  and  locality :  Madison  limestone.  White  Mountain,  Absaroka 
Range;  Arnold  Hague.  Crowfoot  Ridge,  Gallatin  Range,  bed  29;  J.  P. 
Iddings  and  W.  H.  Weed. 


510  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Syringopora  surcularia  n.  sp. 
PL  LXVII,  figs,  ia,  ■lb. 

Similar  to  the  above,  but  larger.  Average  diameter  of  individual 
corallites,  2.5  mm.  Walls  thickened  by  stereoplasma.  Infundibuliform 
di.ssepimental  tissue  well  developed,  spinulose;  the  spines  appear  as  nodes 
of  greater  or  less  prolongation,  often  radially  directed  between  parallel 
dissepiments.  They  are  irregular,  however,  have  no  constant  connection 
with  the  spiniform  septa,  and  never  give  the  corallite  the  septate  appearance 
of  rugose  corals. 

This  species  is,  in  a  general  way,  very  close  to  the  preceding,  but  the 
eye  differentiates  them  at  a  glance  on  the  basis  of  size.  The  walls  of  S.  sur- 
cularia are  more  thickened  by  stereoplasma  than  are  those  of  S.  aculeata, 
and  the  septal  spines,  which  are  embedded  in  it,  appear  to  be  relatively  not 
so  long,  so  numerous,  nor  in  so  many  rows. 

Both  species  are  easily  distinguished  from  S.  multaUenuata  McChes.,  by 
the  fact  that  the  corallites  in  the  latter  often  grow  in  contact  and  are 
scantily  supplied  Avith  septal  spines. 

Formation  and  locality:  Madison  limestone.  White  Mountain,  Absaroka 
Range;  Upper  Gallatin  Valley,  west  of  Bighorn  Pass;  Arnold  Hague. 
Crowfoot  Ridge,  Gallatin  Range,  bed  28;  J.  P.  Iddings  and  W.  H.  Weed. 
Head  of  Gallatin  River,  west  of  Three  River  Peak;  Arnold  Hague. 

MICHELINIA  DeKoninck,  1842. 

MiCHELINIA    PLACENTA    White. 
PL  LXVII,  tigs.  3a,  36. 
Michelinia  {?)  placenta  White,  1883:   Twelfth  Anu.  Kept.  U.  S.  GeoL  Geogr.  Surv. 
Terr.,  Pt.  I,  p.  157,  PL  XXXIX,  figs,  la-1^7. 

This  species  is  known  at  two  localities  in  the  Yellowstone  National  Park. 
It  appears  to  be  the  same  form  described  by  White,  from  Sedalia,  Missouri, 
where  it  occurs  at  tlie  top  of  the  Chouteau  limestone.  I  have  not  seen 
specimens  from  White's  locality,  but  his  description  and  figures  show  the 
two  forms  to  be  very  similar. 

Formation  and  locality :  Madison  limestone,  east  side  of  Gallatin 
River  west  of  Electric  Peak;  divide  between  Gallatin  Valley  and  Panther 
Creek,  near  Bighorn  Pass,  Gallatin  Range,  bed  24;  Arnold  Hague.  Top  of 
the  Chouteau  limestone,  Sedalia,  Missouri. 


LOWEK  CARBONIFEKOUS  FOSSILS.  511 

MENOPHYLLUM  Milue  Edwards  and  Haime,  1850. 

MeNOPHYLLUM  (!)  EXCAVATUM  H.  sp. 
PL  LXVII,  figs,  la,  lb,  Ic,  hi,  le.  If. 

Corallum  simple,  regularly  and  rather  rapidly  expanding,  very  slightly 
curved.  Length  of  an  average  specimen,  41  mm.;  diameter  at  the  top, 
23  mm.  Septa  of  two  series.  Calyce  verj-  deep,  half  or  more  than  half 
the  entire  length  of  the  corallum.  In  the  calyce  the  primary  septa  are  short 
and  the  secondary  septa  shorter  still.  Below,  only  the  primary  septa  are 
well  developed.  They  are  there  sometimes  so  thickened  by  stereoplasma 
as  to  make  the  bottom  of  the  corallum  almost  solid.  There  is  no  columella 
nor  dissepimental  development,  but  a  well-marked  fossula  is  always  present. 

The  deep  calyce  uninterrupted  by  transverse  partitions,  the  smaller 
number  of  septa,  and  large  fossula,  strongly  characterize  this  form 

There  is  only  one  species  of  Menophyllum  known  heretofore,  M.  tentii- 
marginatmn;  and  M.  excavatum  is,  so  far  as  I  am  aware,  the  first  reference  made 
to  the  genus  in  this  country.  This  reference  may,  however,  perhaps  justly 
be  called  in  qviestion,  since  M.  tenuimargin'atwn  is  said  to  possess  crescent- 
shaped  tabulfe,  and  to  be  allied  to  Amjjlexus,  while  M  excavatum  is  without 
tabulae  and  dissepimental  tissue.  On  the  other  hand,  as  seen  in  transverse 
sections,  the  structure  of  the  two  forms  seems  to  be  so  closely  analogous 
that  I  can  not  but  believe  that,  if  not  congeneric,  M.  excavatum  is  at  least 
nearly  allied  to  M.  tenuimarginatum.  It  resembles  the  genus  Cyathaxonia 
in  being  without  tabulae  or  dissepiments,  but  differs  from  it  in  lacking  a 
columella  as  well.  I  have  avoided  the  genus  Petraia,  which  is  pei'haps 
founded  on  a  similar  type,  for  it  is  little  known  and  can  scarcely  be  regarded 
as  well  established.  Nor  do  I  believe  a  reference  to  Zaphrentis  to  be  war- 
ranted, for,  as  before  stated,  M.  excavatum  is  without  endothecal  structure 
except  the  septa,  and  the  manner  in  which  the  ends  of  all  the  septa  are  bent  to 
form  an  inclosing  wall  for  the  fossula  is  very  characteristic. 

Compared  with  M.  tenuimarginatum,  M.  excavatum  has  fewer  primary 
septa,  and  those  of  the  second  order  are  not  so  well  developed. 

The  structures  of  the  earlier  corallum  of  this  coral  have  not  been 
observed.  The  secondary  septa  attain  only  an  inconsiderable  development. 
There  are  about  twenty-six  primary  septa,  which  are  bent  at  the  ends  and  so 
united  as  to  leave  a  large  fossula,  reaching  to  the  center  of  the  theca.     The 


512  GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

fossula  is  bisected  by  a  cardinal  septum,  which  also  reaches  to  the  middle 
and  is  there  connected  with  the  other  septa.  The  theca  and  all  the  septa, 
except  the  cardinal  septa,  are  sometimes  so  thickened  by  stereoplasmic 
deposits  as  to  form  a  nearly  solid  mass,  obscuring  details  of  arrangement. 
This  description  is  taken  from  a  section  below  the  calyce,  well  down  in  the 
septate  portion. 

A  section  through  another  coral,  apparently  at  a  somewhat  later  stage 
than  the  above,  shows  a  very  interesting  condition.  The  septa  on  one  side 
of  the  theca,  about  fifteen  in  number,  are  inclined  toward  a  point,  eccentric, 
and  lying  within  the  diametral  segment  under  discussion.  Their  ends  are 
bent  and  connected  by  a  thick  stereoplasmic  deposit  into  a  counterseptal 
wall.  There  are  twelve  other  septa.  Of  these,  six  on  one  side  and  five  on 
the  other  are  inclined  toward  the  visceral  wall  aforesaid,  and  their  bent 
ends  are  united  into  a  partition  which,  in  one  case,  appears  to  connect  with 
the  counterseptal  wall,  and  in  the  other  is  still  free.  This  leaves  a  wide 
terminally  inflated  fossula,  but  the  septum  occupying  it,  or  cardinal  septum, 
is  very  short.     There  is  no  stereoplasmic  thickening. 

Another  section  through  the  same  specimen,  at  a  point  farther  from 
the  apex,  shows  the  primary  septa  (twenty-nine  in  number)  inclined 
and  Avith  bent  terminations  as  before  described,  but  not  extended  so  as  to 
form  by  their  ends  three  visceral  partitions — a  counterseptal  and  two  alar. 
The  secondary  septa  are  represented  by  low  ridges.  The  fossula  is  strongly 
marked.  It  is  partly  distinguished  by  the  nondevelopment  of  the  fossular 
septum,  which  is  scarcely  more  strong  than  the  two  secondary  septa 
between  which  it  stands;  and  all  the  septa  diminish  in  size  as  they  approach 
the  cardinal  septum. 

Another  section,  farther  toward,  yet  still  some  distance  from,  the  mouth 
of  the  calyce,  shows  thirty  short  primary  septa  with  as  many  still  shorter 
secondary  septa.  The  general  position  alone  of  the  fossula  is  indicated  by 
the  obsolescence  of  the  septa  in  that  region. 

Formation  and  locality:  Madison  limestone,  near  sixmmit  of  ridge, 
west  end  of  Hunter  Peak,  Absaroka  Range;  Upper  Gallatin  Valley  west 
of  Bighorn  Pass ;  Arnold  Hague.  Crowfoot  Ridge,  Gallatin  Range,  bed 
25,  lower  part  of  bed  27,  bed  31 ;  J.  P.  Iddings  and  W.  H.  Weed.  South 
of  Forellen  Peak,  Teton  Range ;  S.  L.  Penfield.  South  base  of  Quadrant 
Mountain,  Gallatin  Range ;  J.  P.  Iddings.  Crowfoot  Ridge,  Gallatin 
Range,  cherty  limestone,  top  of  bed  24 ;  A.  C.  Gill. 


LOVVBK  CARBONIFEKOUS  FOSSILS.  513 

LITH08TR0T10N  Lliwyd,  18G9. 

LlTHOSTROTlON    sj). 

Conilhim  coTni)Oun(l,  massive.  Corallites  small,  about  7  mm.  in 
diameter,  polygonal.  There  are  usually  in  the  neighborhood  of  thirty 
radiating  septa,  alternately  long  and  short.  The  longer  ones  extend  almost 
to  the  center.  Transverse  sections  show  that  the  whole  interseptal  space  is 
more  or  less  vesicular.  Toward  the  penphery  the  vesicular  tissue  is  coarse, 
stretching  in  extended  loops,  among  Avhich,  in  some  individuals,  the  periph- 
eral ends  of  the  septa  lose  themselves.  In  others  the  septa  can  be  traced 
quite  to  the  inclosing  wall.  Toward  the  center  the  vesicular  appears  to 
give  place  to  dissepimental  tissue,  and  regularly  a  series  of  these  dissepi- 
ments equally  distant  from  the  center  are  thickened  and  joined  together  to 
form  a  sort  of  inner  wall.  This  inner  wall  is  circular  in  section,  having  a 
diameter  of  about  4  mm.  The  septa,  too,  appear  thicker  and  denser  at  this 
point,  so  that  the  demarcation  between  the  inner  and  outer  zones  is  well 
marked.  In  the  inner  zone  is  found  localized  dissepimental  tissue,  which 
usually  unites  to  form  one  or  two  concentric  sheaths  about  the  columella. 
The  latter  is  linear,  often  united  at  either  end  with  two  opposite  septa  which 
bisect  the  corallite  and  give  it  a  conspicuous  bilateral  symmetry.  The 
other  primary  septa  terminate  in  one  of  the  columella  sheaths,  as  do  often 
all  the  primary  septa. 

The  calyces  are  deep,  flaring  toward  their  mouth.  The  columella 
projects  from  the  center  of  each,  high,  thin,  and  knifelike  above,  but  below 
thicker  and  complicated  with  ridges.  About  thirty  alternating  septa  are 
present,  of  which  the  primary  ones  descend  into  the  calyce  and  unite  with 
the  columella  at  its  thicker  complicated  base. 

Longitudinal  sections  where  not  central  show  an  outer  vesicular  Z(5ne 
the  strong  vesicle  walls  curving  downward  and  overlapping,  thus  formino- 
by  their  inner  surface  the  so-called  inner  wall  of  the  theca.  Within  this 
are  the  vertical,  parallel,  cut  edges  of  the  septa  intersected  by  dissepiments, 
or  what  appear  sometimes  to  be  upward-arching  tabulfe.  In  a  section 
through  the  columella  the  septa  are  not  seen,  only  the  upcurvino-  tabulse, 
cut  by  the  linear  columella. 

Formation  and  locality :  Madison  limestone,  Crowfoot  Ridge,  Gallatin 

MON  XXXII,  PT  II .33 


514  GEOLOGY  OF  THE  YELLOWSTOiSE  NATIONAL  PARK. 

Range,  bed  28 ;  J.  P.  Iddings  and  W.  H.  Weed.     Head  of  Gallatin  River, 
west  of  Three  River  Peak;  Arnold  Hague. 

CLISIOPHYLLUM  Dana,  1846. 

Clisiophyllum  teres  n.  sp. 

PI.  LXVII,  figs.  2a,  2K  2c,  2(1. 

Corallnm  of  medium  size,  tapering,  slightly  curved,  and  often  laterally 
compressed;  but  little  marked  b}-  constrictions  and  irregularities  of  growth. 
Length  from  75  to  100  mm.;  diameter  of  about  25  mm.  There  are  fifty- 
three  septa  of  the  first  order;  secondaiy  se]Dta  short  and  coalescing  with 
the  primary  ones.  Columella  small,  complex,  composed  of  radiating  and 
concentric  plates.  The  primary  septa  extend  to  the  center  and  are  there 
connected  with  the  columella,  about  which  they  twist.  Dissepimental  tissue 
present  in  moderate  abundance.  Fossula  well  marked,  situated  on  the 
convex  side,  bisected  by  the  fossular  septum. 

This  description  is  not  taken  from  any  one  specimen,  but  is  the  result  of 
observations  made  on  somewhat  fragmentary  material  from  several  localities. 

The  specimen  figured  is  a  somewhat  undersized  individual,  from  the 
summit  of  Three  River  Peak,  referred  to  this  species.  A  section  taken 
where  the  diameter  is  only  7.5  mm.  shows  thirtj^-two  (primary)  septa, 
which  are  thick  and  straight,  joining  the  columella,  like  radii  drawn  from 
the  center  of  a  circle,  and  not  twisting  around  it,  as  they  do  later.  The 
columella  is  large,  apparently  solid,  showing  a  diametric  line  of  greater 
density  in  the  direction  of  the  fossular  septum.  Fossula  large.  Dissepi- 
ments numerous  and  rather  regularly  disposed,  but  not  enough  to  suggest 
tabulae,  which  appear  to  be  absent.  No  secondarj-  septa  have  j'et  made 
tlieir  appearance. 

A  section  taken  near  the  distal  extremity,  where  the  diameter  is  about 
14  mm.,  shows  a  difterent  condition.  It  appears  to  intersect  a  basin- 
shaped  tabula,  or  perhaps  the  floor  of  the  calyce,  for  we  see  the  appearance 
of  a  strong  inner  wall,  which  is  evidently  traversed  obliquely  by  the  plane 
of  the  section.  It  is  decidedly  eccentric,  being  only  about  2.5  mm.  from 
the  peripher}^  at  the  fossula  and  twice  as  far  at  the  opposite  diameter. 
This  tabula  is  apparently  dissepimental  in  its  nature,  and  not  an  inner  wall, 
because  it  does  not  begin  at  the  bottom  of  the  theca,  because  it  is  seen  in 
section  to  be  strongly  divergent,  and  because  it  depends  for  its  expression 


LOWKK  CAUBONIFHUOIS  KOSSILS.  ,         5]  5 

upoa  tlic  primary  septa,  between  wliiili  it  is  renewed  at  each  inten-al.  1^lie 
l)riiiiary  sejjta  are  nu.iv  iiiinicrous  iiere,  and  the  peripheral  portidu,  like  tlie 
tloor  of  the  ealyce,  is  dense  with  stereophisma ;  but  within  the  second  wall 
tlie>-  1)econie  suddenly  extremely  thin,  sweepin<r  iu  a  strong  curve  about 
the  rather  large,  solid  columella.  Dissepiments  nearly  absent.  The  sec- 
ondary septa  also  have  appeared,  but  bend  abruptly  to  the  left  (looking 
into  the  theca)  and  unite  with  the  primary  septa.  The  columella  at  this 
point  has  become  distinctly  compound. 

Formation  and  locality:  Madison  limestone,  limestone  bluff  north  of 
Little  Sunlight  Creek,  Al)saroka  l^ange,  600  feet  above  the  stream;  White 
Mountain,  Aljsaroka  Range;  Arnold  Hague.  East  side  of  Gallatin  River, 
west  of  Electric  Peak;  divide  between' Gallatin  River  and  Panther  Creek,' 
Gallatin  Range;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  bed  28;' 
J.  P.  Iddings  and  W.  H.  Weed.  East  slope  of  Survey  Peak,  Teton  Range;' 
S.  L.  Peutield.     Sununit  of  Three  River  Peak. 

ECHIXODERMATA. 

PLATYCRINUS  Miller,  1831.      ' 
Platycrinus  SYiiMETRicus  Wachsmutli  and  Springer. 

Platycrinus  symvietricus 'W&ch&mwth  and  Springer,  1890:    Geol.  Surv.  llliuois    Vol 
VIII,  p.  186,  PI.  XV,  flg.  8.  '         * 

The  material  examined  is  unsatisfactory  in  that  it  has  not  permitted 
the  determination  of  the  structure  of  the  arms  with  absolute  certainty,  while 
the  character  of  the  vault  is  completely  hidden.  The  suture  lines  of  the 
five  basals  are  quite  in^-isible,  forming  an  apparently  solid  and  ratlier  large 
basal  disk.  The  first  radials,  as  in  P.  symmdricus,  are  slightly  higher  than 
wide ;  indeed,  the  whole  calyx  structure  appears  to  be  as  Wachsnmth  and 
Sjiringer  have  described  it,  except  that  the  suture  lines  are  not  indented  as 
in  the  Iowa  form,  the  whole  surface  being  in  the  plane  of  curvature.  The 
absence  of  this  character  (the  impressed  suture  lines)  may  be  the  result  of 
weathering. 

There  are,  apparently,  thirty  arms  witii  the  same  structure  as  those  of 
P.  si/mmetricus,  but  I  can  not  assert  this  absolutely. 

P.  haydeni  Meek,  described  from  Montana,^  differs  from  the  form  in 

'Meek,  1873:  Ann,  Kept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  469;   White,  1883:  Ibid,  for  1878  Pt  I 
p.  122,  PI.  XXXIII,  fig.  7a.  '  '  ' 


516  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

question  in  being  much  smaller  and  in  having  twenty  instead  of  thirty 
arms.  The  constituent  plates  appear  to  l^e  sculptured,  and  to  have  elevated 
margins,  while  this  is  not  the  case  with  the  form  referred  to  P.  symmetricus, 
although  preservation  may  liave  obscured  this  character. 

I  believe  this  species  to  be  identical  with  that  which  White  described 
and  figured  as  PJatycrtnus  sp.,-  although  it  is  impossible  to  be  certain  upon 
this  point,  as  neither  material  is  very  good. 

Formation  and  localit}' :  ^Madison  limestone,  di^^de  between  Gallatin 
River  and  Panthei-  Creek,  Gallatin  Range ;  head  of  Conant  Creek,  Teton 
Range ;  W.  H.  Weed.     Kinderhook  beds,  Legrand,  Iowa. 

SCAPHIOCRINUS  Hall,  1858. 

SCAPHIOCRINUS   Sp. 

This  form  has  a  rather  small  cup-shaped  calyx,  about  19  mm.  high 
an<l  19  mm.  in  greatest  diameter.  There  are  five  large  basals,  above 
which  are  a  number  of  smaller  plates;  but  the  summit  of  the  calyx  is 
incomplete  and  the  outline  of  the  plates  is  obscured  by  exfoliation,  so  that 
even  the  generic  pcisition  is  only  approximately  correct. 

Formation  and  locality:  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  bed  28;  J.  P.  Iddings  and  W.  H.  Weed. 

BRYOZOA. 

ANISOTRYPA  Ulrich,  1883. 
Anisotrypa  sp. 

This  genus  is  not  yet  known  below  the  Keokuk.  It  is  represented  in 
the  Yellowstone  National  Park  collection  lint  from  one  locality  and  by  a 
single  species.  This  grows  in  a  hollow  club-shaped  zoarium,  enlarged  and 
rounding  at  one  end.  Diameter  of  the  branch,  from  5  to  7  mm.  Height 
of  the  zooidal  tubes,  which  measures  the  thickness  of  the  zoarium,  is  very 
slight,  amountino-  to  less  than  1  nnn.  Diameter,  a))out  0.4  mm.  The  zooidal 
tubes  seem  to  be  nearly  uniform  in  size,  and  I  have  not  been  able  to  dis- 
tinguish clusters  of  larger  cells.     Such  may,  however,  exist. 

This  species  appears  to  be  distinct  from  any  known  representation  of 
the  genus. 


•Wheeler's  U.  S.  Geog.  Surv.  W.  100th  Merid.,  Vol.  IV,  1K77,  p.  81,  I'l.  V,  tig.  2. 


LOWER  CAKBONIFKKOUS  FOSSILS.  517 

Formation  ami  lorality:  Madison  limestone,  Crowfottt  Ridge,  Gallatin 
Range,  bed  31;  J.  P.  Iddinjis  and  W.  II.  Weed. 

ERIDOPORA  Ulfich,  1882. 
Eridopora  (?)  sp. 

Quite  abimdant  at  the  head  of  Conant  Creek,  Teton  Range,  on  speci- 
mens of  ScDiiintIa  madisonenais,  is  a  low  inorusting  bryozoan,  whose  exact 
affinities  among  known  forms  I  have  been  unable  to  determine.  It  seems 
to  be  related  to  the  genus  Fistulipora.  The  colony  is  not  maculate,  the 
cell  walls  rather  thick,  the  cells  very  short,  usually  nearly  square  and 
arranged  in  somewhat  curving  row^s,  about  four  in  the  space  of  1  mm. 
Often  at  the  angle  between  four  cells,  sometinies  situated  laterally  between 
two  of  them,  may  be  seen  one  or  perhaps  two  minute  interstitial  cells, 
which  are  not  seen  on  the  surface  (?).  Younger,  or  perhaps  better  pre- 
served, parts  of  the  colony  show  the  terminal  portions  of  the  cells  to  be 
cylindi'ical,  slantingly  superjacent,  somewhat  contracted  at  the  circular  (?) 
aperture.  It  is  owing  probably  to  erosion  that  the  distal  ])ortions  of  the 
colony  are  missing,  which  leaves  exposed  below  the  angular  crowded  cells 
of  the  colony,  as  seen  under  ordinary  conditions. 

For  a  Fistuliporid  the  intermediate  cells  are  extremely  scarce. 

Formation  and  locality:  Madison  limestone,  head  of  Conant  Creek, 
Teton  Range;  W.  H.  Weed. 

PTILOPORA  McCoy,   1844. 

Ptilopora  sp. 

Zoarium,  an  extended,  Fenestella-like  frond.  Reverse:  Midrilj  large, 
about  0.5  nnn.  in  diameter,  very  prominent,  cylindrical,  without  ornamenta- 
tion except  for  a  median  row  of  strong  distant  nodes.  Branches  gi\en  oft' 
pinnately  at  an  angle  of  about  30°.  Occasionally  from  these  secondary 
branches,  branches  of  a  third  series  are  developed,  but  on  the  distal  side 
only,  at  the  same  angle  (30°).  The  midrib  is  conspicuoush"  larger  than  the 
branches,  which  are  uniform  and  about  fourteen  in  1  cm.  Dissepiments  of 
nearly  the  same  size  as  the  branches,  and,  like  them,  without  ornamentation. 
Fenestrules  square  to  rectangular,  with  an  angular  outline;  about  fourteen 
in  1  cm. 


518  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Obverse :  Midrib  with  two  or  three  rows  of  small,  circular,  zooecial 
apertures  (exact  number  not  ascertained).  Branches  with  a  double  row  of 
alternate  circular  apertures,  three  to  four  opposite  each  fenestrule,  making 
about  iifty  in  1  cm. 

The  genus  Ptilopora  ranges  from  the  Hamilton  to  the  base  of  the  Coal 
Measures,  but,  after  occurring  in  the  Hamilton,  it  does  not  reappear  until  the 
Burlington,  where  a  single  species  is  known.  The  form  from  the  Yellow- 
stone National  Park  is  distinct  from  anything  yet  described. 

Formation  and  locality :  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  ■24;  J.  P.  Iddings. 

STICTOPORELLA  Ulrich,  1882. 
Stictoporella  (!)  sp. 

By  this  name  I  wish  to  designate  a  frondose  Bryozoan  colony  not 
more  than  1  mm.  thick,  but  fully  2  mm.  across,  and  apparently  bifurcate, 
or  at  all  events  bilobate.  Both  surfaces  are  alike,  showing  the  circu- 
lar apertures  of  numerous  thick- walled  pores,  which  are  about  0.5  mm. 
apart  (measuring  from  the  fai'thest  walls),  and  without  any  conspicuous 
order  of  arrangement.  The  intervening  space  is  tilled  in  with  a  large  num- 
ber of  more  or  less  circular  mesopores,  and  the  surface  as  a  whole  is  raised 
at  intervals  into  low  rounded  monticules,  which  factor  seems  not  to  affect 
the  size  or  disposition  of  the  zooidal  openings. 

Formation  and  locality :  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  bed  28;  J.  P.  Iddings  and  W.  H.  Weed. 

FENESTELLA  Lonsdale,  1839. 

This  genus  is  represented  at  several  locaUties,  and  by  a  number 
of  forms,  but  as  the  material  is  both  fragmentary  and  poorly  preserved, 
and  when  fragmentary  can  not  always  be  distinguished  from  Archimedes, 
nor  even  from  Ptilopora,  I  have  not  attempted  to  make  specific  determi- 
nations. 

At  the  locality  on  the  east  side  of  Lamar  Valley,  mouth  of  Soda  Butte 
Creek,  Absaroka  Range,  there  are  probably  two  forms  present.  One  has 
very  slender  branches  and  thin  dissepiments,  leaving  elongate  angular 
feuestrules  from  2  to  3  mm.  long  and  0.5  mm.  Inroad.     This  is  a  very  regular 


LOWER  OAKBONIFEKOUS  FOSSILS.  519 

fonii;  the  branclies  are  tliin,  straight,  and  parallel,  and  the  bifurcations 
infrequent.  The  other  sjjecies  is  tiner,  more  delicate,  and  very  irregular. 
The  material  at  this  locality  is  preserved  as  red  ferruginous  impressions  in 
an  ocher-colored  argillaceous  limestone,  and  no  details  of  structure  could 
be  ascertained. 

At  the  head  of  Conaut  Creek,  Teton  Range,  Fenestella  is  the  most 
common  fossil  jjresent.  It  is  preserved  chiefly  as  casts  in  a  hard,  whitish 
limestone,  and  two  species  can  probably  be  distinguished.  The  first  is 
very  regular  in  growth  and  attains  large  size.  One  incomplete  fragment 
is  5.5  cm.  across.  The  dissejnments  and  branches  are  nearly  equal  in  size, 
the  fenestrules  oval  or  subcircular.  Measuring  radially,  there  are  ten  or 
eleven  fenestrules  in  10  mm.,  and  sixteen  or  seventeen  measui'ing  trans- 
versely. There  are  three  cells  opposite  each  fenestrule.  Another  probably 
distinct  species  is  quite  similar  in  general  appearance,  but  more  delicate 
than  the  last.  Fenestrules  nearly  circular,  eighteen  or  nineteen  occurring 
in  a  radial  direction  of  10  mm.,  and  twenty-tive  or  twenty-six  in  the  same 
distance  measured  at  right  angles  to  the  first. 

Another  species  is  found  in  bed  28,  Crowfoot  Ridge,  Gallatin  Range. 
The  frond  is  quite  regular,  branches  the  same  size  as  the  dissepiments. 
The  fenestrules  are  long-,  elliptical,  eleven  or  twelve  in  10  mm.,  radially 
measured,  and  seventeen  in  transverse  direction.  Twelve  or  thirteen  zooecia 
are  found  opposite  four  fenestrules  (thirty-four  to  thirty-six  in  10  mm.). 
Another  type,  from  the  top  of  bed  24,  Crawford  Ridge,  Gallatin  Range, 
is  perhaps  specifically  related  to  the  last.  It  is  somewhat  coarser,  with 
stronger  branches  and  dissepiments.  Fenestrviles  oval,  about  nine  hi  10  mm. 
radially  and  fifteen  or  sixteen  transversely.  Eleven  to  thirteen  zooecia 
opposite  three  fenestrules  (about  thirty  in  10  mm.). 

ARCHIMEDES  Lesueur,  1842. 

Archimedes  sp. 

The  axis  of  this  form  has  not  been  observed,  but  the  peculiar  manner 
in  which  the  branches  overlie  one  another  can  not  be  mistaken,  and  makes 
the  generic  reference  certain.  It  has  not  been  possible  to  make  sufficiently 
detailed  observations  on  which  to  base  a  specific  description.  The  branches 
are  rather  slender,  not  frequently  bifurcating,  about  twenty-six  in  the  space 


520     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  1  cm.  Dissepiments  more  slender,  regular,  uniform,  twenty  to  twenty- 
three  in  the  space  of  1  cm.  Fenestrules  a  little  longer  than  wide,  subquad- 
rate  in  outline,  angular.  Zooecia  in  two  rows,  circular,  about  three  to  each 
fenestrule,  amounting  to  between  fifty  and  sixty  in  the  space  of  1  cm.  It 
will  be  seen  that  while  the  description  shows  this  form  to  be  close  to  several 
known  species  (A.  distans,  A.  invaginatus  of  the  Chester,  A.  negligens  of  the 
Keokuk),  it  is  not  specifically  the  same  as  any  of  them.  Several  other 
Fenestellids  occur  in  the  same  beds,  l)ut  their  condition  does  not  warrant  the 
attempt  to  identify  them. 

Formation  and  locality :  Madison  limestone,  south  of  Forellen  Peak, 
Teton  Range  ;  S.  L.  Penfield. 

CRANIA  Retzius,  1781. 

Crania  l^evis  Ke3^es. 

ri.  Lxviii,  fig.  irt. 

Crania  Iwvis  Keyes,  1894:  Geol.  Surv.  Missouri,  VoL  V,  Pt.  II,  p.  40. 

The  single  specimen  Ijy  which  this  species  is  represented  is  somewhat 
crushed,  but  api)ears  to  be  of  an  elliptical  or  subcircular  shape,  the  larger 
diameter  being  23  mm.,  the  shorter  about  19  mm.  Beak  lying  in  the  short 
diameter,  and  eccentric  with  regard  to  the  long  one.  Side  nearest  to  it  some- 
what truncated.  Convexity  moderate,  about  7.15  mm.  Surface  smooth, 
without  radiating  striae,  but  with  fine  concentric  lines  of  growth. 

Keyes's  description,  which  is  unaccompanied  by  figures,  is  very  brief 
and  contains  little  which  is  of  value  in  identifying  species.  According  to 
the  original  description,  C.  Imvis  is  rather  above  the  medium  size,  somewhat 
depressed,  apex  subcentral,  outline  subcircular,'  ti-uncate.  Smooth  but  for 
fine  concentric  lines.  In  all  these  points  the  Yellowstone  National  Park 
form  agrees  with  C.  Icevis,  which  is  furthermore  said  to  occur  in  rocks  of 
Waverly  and  Burlington  age. 

Only  four  species  of  Crania  have  been  described  from  Carboniferous 
strata :  Crania  Imins  Keyes,  Crania  rowleyi  Grurley,  Crania  permiana  Shu- 
mard,  and  Crania  modesta  White  and  St.  John.  The  first  two  are  of 
Waverly  age,  the  last  two  of  Upper  Carboniferous.  It  is  extremely 
improbable  that  either  C.  modesta  or  C.  permiana  would  be  found  in  these 
beds  associated  with  low  Lo^A^er  Carboniferous  fossils,  while  C.  rowleyi  is 


LOWER  CAKBONIFEKOUS  FOSSILS.  521 

much  smaller  than  the  form  imder  discussion,  ;uk1  ornamented  with  closely 
arrano'od  radiating-  stria'.  Thus  there  is  presuin})tive  as  well  as  direct 
evidence  that  the  individual  here  referred  to  C.  Iccvis  Keyes  is  correctly 
identitied. 

Formation  and  locality :  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  top  of  lied  24;  J.  V.  Idding-s.  Chouteau  limestone,  Louisiana, 
Missouri.      Burlington  limestone,  Louisiana,  Missouri. 

RHIPIDOMELLA  Oehlert,  1880. 
Rhipiuomella  michelini  Le'veille. 

Terehratula  michelini  Li'veille,  1835:  M6in.  Soc.  Giiol.  France,  1st  series,  Vol.  II,  p.  39, 

PI.  II,  tigs.  14-17. 
Orthis  michelini  Yandell  and  Sliutuard,  1847:  Coutributious  Geol.  Kentuckj^,  p.  21, 

Wiucbell  (A.),  1865:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  116.     (?)  Winchell  (A.), 

1870 :  Proc.  Am.  Phil.  Soc,  Vol.  XI,  p.  251.     ( ?)  Hall,  1883 :  Second  Ann.  Eept. 

jSTew  York  State  Geologist,  PI.  XXXVI,  figs.  19-21. 
Rhijmlometla  michelini  Hall  and  Clarke,  1892:  Pal.  Xew  York,  Vol.  VIII,  Pt.  I,  pp. 

19J:-225,  PI.  6rt,  fig.  12. 

This  form  is  rare,  and  the  material  almost  too  poor  for  identification. 
As  far  as  it  is  possible  to  judge,  it  is  identical  with  B.  michelini  as  identified 
from  the  Waverly  of  Richfield,  Summit  County,  Ohio,  and  from  Cuyahoga 
County,  Ohio.  The  latter  is  a  small  form,  subcircular;  width,  9.5  mm; 
length  slightly  less,  not  very  gibbous,  marked  by  about  one  hundred 
regular  strise. 

RhipidomeUa  michelini  occurs  in  two  localities  in  the  Yellowstone 
National  Park. 

Formation  and  locality:  Madison  limestone,  amphitheater  east  of 
Bannock  Peak,  Gallatin  Range,  bed  27;  east  side  of  Lamar  Valley,  mouth 
of  Soda  Butte  Creek;  W.  H.  Weed.  Waverly  age,  south  of  Louisville  and 
near  Lebanon,  Kentucky;  Newark,  Granville,  Richfield,  Bagdad,  etc., 
Ohio;    Shafers,   Pennsylvania;   Lake  Valley  mining  district,  New  Mexico. 


522  GEOLOGY  OF  THE  YELLOWSTOiSTE  NATIONAL  PARK. 

ORTHOTHETES  Fischer  de  Waldheim,  1830. 
Orthothetes  in^equalis  Hall. 

PI.  LXVIII,  fig.  3«,. 

Orthis  inequalis  Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  490,  PI.  II,  figs.  6a-6c. 
Streptorhynchus  inaqualis  A.  Wincbell,  1865:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  117. 
Strei)tori/li)tchus  eqitimlvis  Hall  and  Whitfield,  1877:  Kiug's  U.  S.  Geol.  Espl.  40th 

Par.,  Vol.  IV,  p.  252,  PI.  IV,  figs.  1,  2. 
Utreptorhynchus  (vquivalvis  Hall,  1883:  Second  Ann.  Eept.  New  York  State  Geologist, 

PI.  42,  figs.  20-23. 
Orthothetes  incvqualls  Hall  and  Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  PI.  9a, 

figs.  20-23. 

Orthothetes  incequalis  is  extremely  abundant  in  the  limestones  and  cal- 
careous sandy  shales  of  the  Yellowstone  National  Park.  The  lai-gest  shells 
measure  25  mm.  in  length  by  38  mm.  in  breadth,  but  the  average  is 
somewhat  smaller  than  this.  The  shape  is  semicircular.  The  outline  is 
somewhat  contracted  at  the  cardinal  extremities,  and  the  hinge  line  slightly 
shoi'ter  than  the  greatest  Avidth  of  the  shell.  The  surface  is  marked  by 
numerous  elevated,  sharp,  radiating  striae,  about  fourteen  in  the  space  of 
.5  mm.,  which  leave  between  them  intervals  wider  than  the  strife  them- 
selves, from  which  they  abruptly  rise.  They  do  not  bifurcate,  but  in  the 
widening  intervals  which  result  from  their  radiating  direction  new  striae  are 
from  time  to-  time  introduced.  They  sometimes  become  much  crowded 
through  the  center  of  the  shell  and  around  the  periphery.  The  stria?  are 
not  all  of  the  same  size.  Sometimes  they  are  alternately  large  and  small; 
sometimes  every  fourth  one  is  large,  but  more  often  there  is  no  conspicuous 
arrangement.  They  are  crossed  by  numerous  fine  concentric  sti-iae  charac- 
teristic of  the  genus.  As  a  result  of  the  surface  structure  just  mentioned, 
casts  of  the  exterior  are  misleading  in  that  they  seem  to  present  a  form 
with  broad,  close-set,  and  bifurcating  radiating  plications. 

The  dorsal  valve  is  usually  gibbous,  but  sometimes  is  more  gently 
curved.  As  a  rule  the  curvature  is  regular  from  beak  to  frontal  margin,  with 
a  somewhat  prominent  umbo;  but  forms  occur  where  the  umbo  is  flattened 
and  there  is  a  point  of  prominent  elevation  in  the  middle  of  the  valve;  or, 
where  the  shell  is  depressed,  with  almost  a  geniculation  near  the  margin. 


LOWER  CAKBONIFEKOUS  FOSSILS.  523 

The  ventral  valve  is  nearly  flat.  Sometimes  it  is  slightly  convex,  but 
usiiallv  the  umbonal  repfion  alone  is  convex  and  tlie  outlying  portions  of 
the  shell  are  somewhat  excavated. 

Both  valves  are  often  marked  by  concentric  coiTugations,  due  to  unequal 
growth,  while  old  shells  are  sometimes  plicated  into  loose  and  irregular 
radiating  folds  or  corrugations  along  the  periphery. 

The  generic  identitication  of  this  form,  as  represented  in  the  Yellow- 
stone National  Park,  I  can  not  regard  as  doubtful.  The  septum  in  the 
ventral  valve  characteristic  of  Derbya,  the  only  other  genus  with  which  it 
could  be  confused,  did  not  exist  here. 

Orthothetes  inflatns  is  somewhat  larger  than  0.  imequaUs.  The  height 
of  the  area  is  said  to  be  one-third  as  great  as  its  width,  and  three  times  the 
width  of  the  foramen.  It  is  described  as  differing  from  0.  incBqualis  in 
having  a  much  more  ventricose  dorsal  valve  and  in  the  nmch  greater  height 
of  the  area  of  the  ventral  valve,  in  which  the  foramen  is  about  three  times 
as  high  as  wide,  while  in  that  species  it  is  much  wider  than  high.  The 
strife  are  also  coarse  and  more  elevated.'  In  the  Yellowstone  National 
Park  form  the  area  is  many  times  as  wide  as  high  and  the  foramen  is  A^ery 
slightly  higher  than  it  is  wide.  The  dorsal  valve  is  also  much  less  inflated 
than  the  corresponding  valve  flgured  by  Hall  and  Clarke  (loc.  cit.,  PI.  9ff, 
fig.  24) 

I  have  not  identified  0.  uiflatus  in  the  collection  studied. 

Formation  and  localitv:  Madison  limestone,  near  summit  of  ridsre, 
west  end  of  Hunter  Peak,  Absaroka  Range;  limestone  blutf  north  of 
Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  stream;  Ai-nold 
Hague.  East  side  of  Gallatin  River,  west  of  Electric  Peak;  divide 
between  Gallatin  River  and  Panther  Creek,  Gallatin  Range;  east  face  of 
Antler  Peak,  Gallatin  Range;  saddle  west  of  Antler  Peak,  Gallatin  Range; 
amphitheater  west  of  Bannock  Peak,  Gallatin  Range,  bed  26;  amphitheater 
east  of  same,  bed  28;  W  H.  Weed.  Crowfoot  Ridge,  top  of  bed  25; 
J.  P.  Iddings  and  G.  M.  Wright.  Same,  bed  26;  lower  part  of  bed  27; 
upper  part  of  bed  27;  beds  28,  29,  31;  J.  P.  Iddings  and  W.  H.  Weed. 
South  of  Forellen  Peak,  Teton  Range;  northwest  slope  of  same;  S.  L. 
Penfield.  West  of  Antler  Peak,  Gallatin  Range;  north  of  Bighorn  Pass, 
Gallatin  Range;  A.  C.  Gill.     Crowfoot  Ridge,  Gallatin  Range;  top  of  bed 


'  White  aud  Wliitfield,  loc.  cit.,  p.  293. 


524  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

24;  J.  P.  Iddings.  Head  of  Conant  Creek,  Teton  Range;  north  of  Owl 
Creek,  northeast  skipe  of  Teton  Range;  north  end  of  Teton  Range,  north 
of  Owl  Creek;  Snake  River  Valley,  east  of  Two  Ocean  Plateau;  W.  H. 
Weed.  Limestone  bluff  soutli  side  of  Soda  Butte  Creek,  northwest  of 
Abiathar  Peak;  J.  P.  Iddings.  North  side  of  North  Fork  of  Mill  Creek, 
Snowj^  Range;  Louis  V.  Pirsson.  Under  quartzite  ridge  north  side  of  Burnt 
Fork.  Kinderhook  age,  Burlington,  Iowa;  Dry  Canyon,  Oquirrh  Mountain, 
Utah:  Montana. 

Orthothetes  sp. 

This  species  is  represented  by  a  single  imperfect  specimen,  which  seems 
to  differ  from  any  of  the  other  forms  recognized  in  the  collection.  It  is 
about  the  size  of  Berhya  keokuk0),  and  much  larger  than  Orthothetes  inaqualis, 
but  the  surface  ornamentation  is  different  from  either.  While  the  striae  in 
D.  keokuk  (?)  are  rounded  and  contiguous,  in  this  form  the}'  are  narrow  and 
threadlike,  more  as  in  0.  incequaUs,  the  space  between  any  two  stria?  being- 
wider  than  the  stria'  themselves.  Thus  the  surface  as  a  whole  is  more 
coarsely  striate  than  in  0.  'niceqiiatis,  although  the  striae  themselves  are  of 
the  same  size  and  character. 

This  form  is  without  the  median  septum  peculiar  to  the  genus  Derbya. 

Formation  and  localit}^:  Madison  limestone,  head  of  Conant  Creek, 
Teton  Range;  W.  H.  Weed. 

DERBYA  Waagen,  1884. 

Derbya  keokuk  Hall  (?) 

Orthis crenistriaYandeW  aud  Sbumard,  184:9:  Oontributious  Geol.  Kentucky,  pp.  19,  21. 
Orthis  l-eolcuh  Hall,  1858:  Geol.  Siirv.  Iowa,  Vol.  I,  Pt.  II,  p.  040,  PI.  XIX,  tigs.  5a,  5b. 

Keyes,  1895 :  Geol.  Surv.  Missouri,  Vol.  V,  Pt.  II,  p.  63. 
StreptorhyHchus  Jceolcul-  Hall,  1883:  Second  Auu.Eept.  NewY^ork  State  Geologist,  PL 

XLI,  figs.  1-3. 
Berhya  leohil-  Hall  aud  Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  p.  262,  PI.  XI, 

figs.  1-3. 

This  form  occurs  only  at  a  single  locaUty,  and  tlie  material  present  is 
highlv  unsatisfactory.  It  seems  to  be  nearer  to  D.  keokuk  than  to  any 
Strophomenoid  shell  with  which  I  am  acquainted,  but  its  exact  generic 
position  can  not  be  ascertained.  It  is  about  twice  the  size  of  even  the 
largest  specimen  of  Orthothetes  iiKeqiialis,  finely  and  evenly  striate,  the  strife 
round,  proximate,  and  crossed  by  fine,  lamellose,  concentric  striae 


LOWER  CAUBOXIFEROUS  FOSSILS.  525 

Formation  and  locality:  i^Iadison  limestone,  Crowfoot  Ridj^e,  Gallatin 
Rang-e,  bod  31;  J.  P.  Iddinps  and  W.  II.  Weed.  Keokidc  age,  Keokuk, 
Iowa;  Warsaw  and  Xauvoo,  Illinois;  New  Providence,  Indiana;  Clark 
County,  Mis-souri;   Nevada. 

LEPT.ENA  Dalman,  1828. 

Lkpt.ena  rhomboidalis  Wilckens. 

Conchitarhomboidalis  Wilckens,  17G9:  Nachiicht  von  selten  Versteinernngen,  p.  77, 

PI.  VIII,  figs.  43,  44. 
Lepta-na  tenHistriata  Hall,  1847:  Pal.  New  York,  Vol.  I,  p.  108,  PI.  3lA,  tigs,  ia-ig. 
mrophomena  rhomboidalis  White,  1875:  Wheeler's  Espl.  Surv.  W.  100th  Merid.,  Vol. 

IV,  p.  85,  PI.  V,  fig.  5.     Hall  and  Whitfield,  1877 :  King's  U.  S.  Geol.  Expl.  40th 

Par.,  Vol.  IV,  p.  253,  PI.  IV,  fig.  4.     Waleott,  1884:  Mon.  U.  S.  Geol.  Survey, 

Vol.  VIII,  p.  118. 
Lepta-na   rJwmboidalis    Hall   and   Clarke,    1S02:   Pal.  New  York,  Vol.  VIII,  Pt.   I, 

p.  279,  PI.  VIII,  figs.  17-31;  PI.  loA,  figs.  40-42;  PI.  20,  tigs.  21-24. 

The  amazing  stratigraphic  and  geographic  range  of  this  species  makes 
it  too  well  known  to  require  any  additional  description.  It  is  a  compara- 
tively rare  form  in  the  Yellowstone  National  Park,  and  is  found  only  in  the 
lower  part  of  the  iMadison  limestone. 

Formation  and  locality:  Madison  limestone,  Ci'owfoot  Ridge,  Gallatin 
Range,  top  of  bed  25 ;  J.  P.  Iddings  and  G.  M.  Wright.  West  of  Antler 
Peak,  Gallatin  Range;  A.  C.  Gill.  Crowfoot  Ridge,  Gallatin  Range,  top  of 
bed  24;  J.  P.  Iddings.  East  side  of  Lamar  Valley,  mouth  of  Soda  Butte 
Creek,  Absaroka  Range;  Arnold  Hague.  Universally  distributed,  from  the 
Trenton  to  the  Waverly. 

CHONETES  Fischer  de  Waldheim,  1837. 

Chonetes  loganensis  Hall  and  Whitfield. 

PI.  LXVIII,  figs.  5a.  56,  5c. 

Chonetes  loganensis  Hall  and  Whitfield,  1877:  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol. 
IV,  p.  252,  PI.  IV,  fig.  9. 

This  form  is  very  abundant  in  the  Carboniferous  limestones  of  the  Yel- 
lowstone National  Park.  Specimens  have  been  examined  from  a  number 
of  localities,  and  they  can  be  referred  without  hesitation  to  C.  loganensis  Hall 


526  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

and  Whitfield.  In  general,  C.  loganensis  is  almost  exactly  similar  to  C.UUnois- 
ensis  Wortlien.  Hall  and  Whitfield  say  (loc.  cit.,  \).  254):  "The  species 
resembles  somewhat  C.  iU'nioisensis  Worthen,  from  the  Burlington  limestone, 
in  the  size  and  convexity  of  the  valve,  and  also  in  the  strise,  but  dift'ers  in 
the  greater  proportional  length  of  the  hinge  line  and  in  the  flattening  of  the 
mesial  jjortion." 

Chonetes  loganensis  is  described  and  figured  with  submucronate  alar 
extensions,  but  this  character  is  a  restoration,  for  the  type  specimen  is  imper- 
fect; and  an  incorrect  one,  for  a  study  of  considerable  material,  including 
Hall  and  Whitfield's,  as  well  as  my  own,  shows  that  the  prevailing  form  is 
subcircular  with  parallel  rectilinear  sides  which  meet  the  hinge  line  at  nearly 
a  right  angle,  the  corners  l^eing  usuall}'  either  rectangular  or  rounded. 

The  mesial  flattening  referred  to  is  well  sh(nvn  in  tlie  type  specimen, 
but  it  is  not  a  constant  character,  and,  in  fact,  the  curvature  seems  to  be 
most  often  regular  and  even.  On  the  other  hand,  specimens  of  C.  ilUiiois- 
ensis  Worthen,  from  one  of  the  type  localities,  shows  exactly  the  same  range 
of  variation,  some  having  a  distinct  sinus  or  flattening,  just  as  has  been 
observed  in  C.  loganensis.  In  general  I  have  been  unable  to  discover  any 
constant  differences  which  might  distinguish  the  two  species. 

The  surface  ornamentation  of  C  loganensis,  wherever  shown  on  areas 
which  are  not,  as  usual,  badly  exfoliated,  consists  of  fine,  flexuous,  often 
bifurcate,  radiating  striae,  which  are  rather  angular  and  are  separated  by 
interspaces  about  equal  to  their  own  diameter.  These  are  crossed  by  very 
fine,  threadlike,  concentric  strise. 

The  average  size  of  mature  shells  is:  breadth,  14  mm.;  length,  10  mm.; 
but  the  dimensions  run  up  as  high  as  16  mm.  in  breadth  by  11.5  nun. 
in  length.     The  radiating  stria?  number  about  one  hundred  and  fifty. 

It  is  impossible  to  confuse  tins  with  the  only  other  species  of  Chonetes 
known  from  the  Yellowstone  National  Park.  The  radiating  striae  are  finer 
and  much  more  numerous,  the  shell  itself  is  less  tumid,  and  the  outline 
is  more  quadrate. 

Formation  and  locality:  Madison  limestone.  Hunter  Peak,  Absaroka 
Range;  White  Mountains,  AlDsaroka  Range,  just  below  Quadrant  quartzite; 
T.  A.  Jaggar.  East  side  of  Gallatin  River,  west  of  Electric  Peak ;  east 
of  Antler  Peak,  Gallatin  Range;  saddle  west  of  Antler  Peak,  Gallatin 
Range;    amphitheater    east   of    Bannock  Peak,  Gallatin   Range,  bed  27; 


LOWER  CARBONIFEROUS  FOSSILS.  527 

W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25,  bed  26,  bed 
28,  bed  29,  bed  31;  J.  P.  Iddings  and  G.  M.  Wright.  South  of  Forellen 
Peak,  Teton  Range;  nortlnvest  slope  of  same;  S.  L.  Peiifield.  Head  of 
Conant  Creek,  Teton  Range;  north  of  Owl  Creek,  northeast  slope  of  Teton 
Range;  north  of  Owl  Creek,  north  end  of  Teton  Range;  W.  H.  Weed. 
Limestone  bluff  south  side  of  Soda  Butte  Creek,  northwest  of  Abiathar 
Peak,  Absaroka  Range;  J.  P.  Iddings.  North  side  of  north  fork  of  Mill 
Creek,  Snowy  Range;  J.  P.  Iddings  and  Louis  V.  Pirsson.  Slide  east  side 
of  Gallatin  River,  below  Fan  Creek;  under  Quartzite  Ridge,  north  side  of 
Burnt  Fork.  Beds  of  the  age  of  the  Waverly  group,  Wasatch  Range, 
Utah. 

Chonetes  ornatus  Shuniard. 

PI.  LXVIII,  flgs.  4rt,  ib,  ic,  id. 

Chonetes  ornata  Sbuniard,  1855:  Geol.  Kept.  Missouri,  p.  202,  PI.  C,  figs,  la-lc.    Keyes, 
lS9i:  Geol.  Surv.  Missouri,  Vol.  V,  Pt.  II,  p.  53,  PI.  XXXVIII,  flg.  2. 

This  also  is  a  common  species  in  the  limestones  of  the  Park,  though 
perhaps  less  abundant  than  the  preceding.  It  differs  somewhat  from  Shu- 
mard's  description,  but  agrees  with  specimens  which,  I  have  every  reason 
to  believe,  are  correctly  referred  to  Shumard's  species. 

This  form  is  often  cpiite  highly  inflated  with  flat  and  depressed  trian- 
gular wings,  a  character  not  sufficiently  emphasized  b}^  the  author. 
Another  misleading  point  is  that  the  species  is  described  and  figured  as  if 
Avith  submuci'onate  alations.  I  have  not  seen  this  feature,  at  least  to  any 
extent,  in  a  series  of  specimens  from  both  the  Chouteau  and  Lithf)graphic 
limestones.  Usually  the  cardinal  angle  is  but  slightly  less  than  90°. 
However,  it  often  happens  that  the  anterior  portion  of  the  shell  is  concealed 
by  rock,  so  that  the  apparent  shape  is  that  of  Shumard's  figure.  This  con- 
dition is  quite  deceptive,  but  I  have  rarel}'  failed  to  find  the  nearl}"  square 
alar  angle  upon  removing  the  superincumbent  matrix.  In  its  large  forms 
this  species  measures  13  mm.  (over  6  lines)  along-  the  hinge  line,  and 
8  mm.,  or  nearly  4  lines,  in  length,  while  some  imperfect  examples  evi- 
dently exceed  these  dimensions.  I'hese  data  are  derived  from  the  study  of 
material  from  the  Mississippi  Valley. 

In  the  Yellowstone  National  Park  representatives  of  Chonetes  ornatns 
are  in  nearly  perfect  accord  with  the  larger  forms  coming  from  Missomi. 


528  GEOLOGY  OF  THE  YELLOWSTO:E»rE  NATIOjSTAL  PAEK. 

Breadth,  14.5  mm.,  or  more;  length,  8  to  8.5  mm.  Radiating  striae  from 
forty  to  fifty  in  number,  often  bifurcating  toward  the  anterior  border, 
crossed  by  numerous  thread-hke  concentric  stria?.  Number  of  sjjines  not 
determined  with  certainty;  two  or  three,  perhaps  more,  on  either  side  of 
the  beak. 

There  can  be  no  difficulty  in  distinguishing  this  species  from  C.  Jogan- 
ensis,  even  where  both  occur  in  the  same  beds.  It  is  somewhat  smaller, 
more  coarsely  striate,  and  "very  much  more  gibbous.  The  alation  also  is 
more  strikino-  and  forms  a  characteristic  feature. 

The  smaller  type  of  C.  ornatns  has  sometimes  been  confused  with  C. 
logani  var.  aurora  Hall;  but  the  surface  ornamentation  of  the  latter  is  very 
distinctive. 

I  venture  to  predict  that  this  species,  or  at  least  the  form  from  the 
Chouteau  limestone,  will  be  found  to  be  the  same  as  C.  loganl  Norwood  and 
Pratten. 

Formation  and  locality:  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  Crowfoot  Ridge,  Grallatin  Range,  bed  25 ;  J.  P. 
Iddings  and  G.  M.  Wright.  South  slope  of  Quadrant  Mountain,  Gallatin 
Range ;  A.  C.  Gill.  South  base  of  same ;  cherty  belt.  Bighorn  Pass,  Gal- 
latin Range;  J.  P.  Iddings.  Crowfoot  Ridge,  Gallatin  Range,  bed  24; 
A.  C.  Gill.  North  of  Owl  Creek,  northeast  slope  of  Teton  Range;  W.  H. 
Weed.  Limestone  bluff  south  side  of  Soda  Butte  Creek,  northwest  of 
Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings.  Chouteau  limestone, 
Louisiana  and  Hannibal,  Missouri. 

PRODUCTELLA  Hall,  1867. 
Productella  cooperensis  Swallow. 

PL  LXVIII,  figs.  8a,  8h,  8c,  9a,  9b. 

Productus  cooperensis  Swallow,  1860:  Trans.  St.  Louis   Acad.  Sci.,  Vol.  I,  p.  640. 
Winchell  (A.),  1865:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  115. 

Shell  small.  Ventral  valve  strongly  arched,  beak  rather  produced 
and  incurved.  Ventral  valve  slightly  concave  or  subplane  over  the  vis- 
ceral region  and  more  or  less  shari)ly  geniculate  near  the  margin.  Sur- 
face marked  by  nearly  obsolete  spiniferous  ridges  and  by  strong  concentric 
wrinkles,  especially  noticeable  about  the  posterior  portion  and  near  the 


LOWEli  CARBONIFEROUS  FOSSILS.  529 

]\m<re.  The  eai-s  of  the  ventral  valve  are  furnished  with  a  bunch  of  spines. 
The  dorsal  valve  is  similarly  ornamented  except  that  it  does  not  appear  to 
be  spinose  and  the  radiating  ridg'es  become  grooves.  However,  as  the 
convex  side  is  usually  presented  to  view,  the  surface  seems  a  counterpart  of 
the  other  valve.  Viewed  from  this  side,  two  broad,  strong,  slightly  diver- 
gent grooves  are  seen  near  the  hinge  line,  marking  off  the  somewhat 
upturned  ears. 

PI.  LXVIII,  figs.  9a,  db,  show  a  type  which  I  had  thought  to  consti- 
tute a  distinct  variety,  but  more  careful  comparison  shows  that  this  conclusion 
was  not  warranted. 

P.  cooperensis  is  said  by  Swallow  to  be  common  in  the  Chouteau  lime- 
stone of  Cooper  County,  Missouri.  I  have  studied  a  large  series  of  speci- 
mens from  the  Chouteau  limestone  of  Stevens  Fork,  Missouri,  and  Chouteau 
Springs,  Cooper  County,  IVIissouri.  This  material  agrees  with  Swallow's 
description  and  is  specifically  identical  with  the  specimens  from  the  Yellow- 
stone National  Park. 

^  P.  cooperensis  proves  to  be  a  variable  form.     Many  of  the  differences 
noticed  are  without  doubt  due  to  differences  in  age,  but  a  considerable 
range  of  variation  can  not  be  ascribed  to  this  factor.     The  ventral  valve  is 
sometimes  low  and  flat,  like  that  figured  by  Hall,^  but  often  it  is  highly 
arched.     The   dorsal  valve   is   moderately  concave,   semielliptical;    beak 
small,  depressed.     Often  nearly  plane  at  first,  or  sometimes  concave,  Ixit 
later  becoming  geniculate  at  the  margin,  and  the  geniculate  portion  is  often 
considerably  prolonged.     There  is  also  a  variation  in  size,  some  large  shells 
being  depressed  and  immature  in  appearance,  while  much  smaller  ones  are 
highly  arched  and  look  fully  grown.     No  reliance  can  be  placed  upon  the 
spines   for  specific   identification.     They  are  scattered  over  the  surface, 
sometimes  irregularly,  sometimes  in  rows,  sometimes  nearly  absent.     There 
is  often  a  bunch  of  strong  spine  bases  on  the  rather  small  ears;  but  this, 
too,  is  not  a  constant  feature. 

^rhe  specific  integrity  of  P.  concentrica  Hall,  P.  shumardiana  Hall,  and 
P.pyxidata  Hall  has  often  been  questioned.  As  early  as  1865  WinchelP 
stated  the  opinion  that  P.  shumardiana  and  P.  pi/xidata  M'e  both  synonyms 

'  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  PI.  VII,  fig.  2. 
s  Winchell,  1865 :  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  115, 
MON  XXXII,  PT  U 34 


530  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

for  P.  concentrica,  and  in  1888  Herricki  says:  " Froductus  shumardiana  is 
doubtless  identical  with  P;  spinuUcostatus  H.,  P.  concentricus  H.,  and  P. 
pyxklata  H." 

I  believe  that  Productella  shumardiana  and  P.  concentrica  are  distinct,  but 
the  former  is  probably  identical  with  P.  pijxidata.  I  also  feel  confident  that 
P.  cooperensis  will  be  found  to  be  the  same  as  P.  concentrica,  but,  not  having 
the  material  to  prove  the  point,  I  have  used  Swallow's  name,  which, 
however,  will  have  to  be  dropped  in  case  my  suspicions  prove  coiTect. 

Productus  cooperensis  (f)  of  WinchelP,  from  Sciotoville,  I  believe  to  be 
a  quite  different  species,  and  have  accordingly  omitted  this  citation  from 
the  synonymy. 

Formation  and  locaHty.  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  24;  J.  P.  Iddings.  Same,  lower  part  of  bed  27;  J.  P. 
Iddings  and  W.  H.  Weed.  East  side  of  Gallatin  River,  west  of  Electric 
Peak;  George  M.  Wright.  East  face  of  Antler  Peak,  Gallatin  Range; 
W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25;  J.  P. 
Iddinffs  and  G.  M.  Wright.  Summit  of  Three  River  Peak,  Gallatin  Range; 
J.  P.  Iddings.  North  of  Owl  Creek,  northeast  slope  of  Teton  Range; 
W.  H.  Weed.  Kinderhook  age,  Burlington,  Iowa,  Cuyahoga  shale  of  the 
Waverly  group,  Richfield,  Lodi,  Bagdad,  Burbank,  Cuyahoga  Falls,  etc.; 
Chouteau  limestone,  Stevens  Fork,  Missouri;    Chouteau  Springs,  Cooper 

County,  Missouri. 

Productella  alifera  n.  sp. 

PI.  LXVIII,  figs.  lOfl,  106,  10c. 

Shell  rather  above  medium  size.  Ventral  valve  strongly  arched  both 
longitudinally  and  transversely.  A  transverse  section  near  the  umbo 
would  be  subquadrate,  broadly  flattened  on  top  (but  not  impressed);  sides 
curving  sharply  downward,  but  turning  again  near  the  margin  for  a 
sfio-htly  projecting  lip.  Longitudinal  section  also  slightly  flattened  about 
the  middle;  posterior  slope  strongly  deflexed  and  incurved;  anterior  slope 
falling  more  gently  and  reflexed  toward  the  margin.  Sometimes,  however, 
this  valve  is  geniculate  in  front  and  somewhat  spread  out  posteriorly.  The 
beak  is  formed  by  the  gradual  convergence  of  the  lines  defining  the  body 


1  Herrick,  1888 :  Bull.  Denison  Univ.,  Vol.  Ill,  Pt.  I,  p.  32. 
sProc.  Am.  Phil.  Soc,  Vol.  11,  1870,  p.  249. 


LOWEIl  CARBONIFEROUS  FOSSILS.  531 

of  the  shell,  which  falls  away  quite  rapidly  on  either  side,  giving  rise  to 
large  })roduced  and  flattened  ears.  This  is  a  variable  feature,  however, 
and  the  lateral  margins  may  meet  the  hinge  line  at  nearly  right  angles. 

Dorsal  valve  only  slightly  convex,  but  geniculate  toward  the  anterior 
margin. 

Surface  nearly  smooth,  mai-ked  by  numerous  gentle  rugosities,  and  by 
very  fine,  confused,  radiating  strije,  which  may  be  the  result  of  exfoliation 
joined  with  shell  structure. 

The  dimensions  of  a  slightly  undersized  auriculate  specimen,  figured 
on  PI.  LXVIII,  fig.  10c,  are:  Length,  25  mm.;  width  at  hinge  line,  44  mm.; 
width  a  little  in  front  of  hinge  line,  25.5  mm.  The  largest  specimen 
observed,  a  spreading  individual,  with  a  nearly  vertical  posterior  outline, 
measures  54.5  mm.  in  length;  width  probably  about  the  same. 

Formation  and  locality:  Madison  limestone,  limestone  bluff"  south 
side  of  Soda  Butte  Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range; 
J.  P.  Idding-s. 

PRODUCTUS  Sowerby,  1814. 


■"o" 


Peoductus  scabriculus  Martin. 
PI.  LXIX,  figs,  la,  7b,  7c,  Id. 

Anomites  scahriciilus  Martiu,1809:  Petrefacta  Derbieusia,  p.  8,  PI.  XXXVI,  fig.  6. 
Productus  scabriculus  Norwood  and  Pratten,  1854:  Jour.  Acad.  Nat.  Sci.  Philadelphia. 

(2),  Vol.  Ill,  p.  17.    Marcou,  1858:   Geol.  North  America,  p.  47,  PI.  V,  fig.  6. 

Newberry,  1861:   Ives's  Rept.  Colorado  River  of  the  West,  Pt.   II,  p.  125. 

?Geinitz,  1866:  Carbon,  und  Dyas  in  Nebraska,  p.  54. 

This  form  was  at  first  identified  with  Productus  netvherryi  Hall.  It 
closely  resembles  the  figure  of  P.  netvherryi  (Pal.  New  York,  Vol.  VIII, 
Pt.  I,  1892,  PI.  XVII,  fig.  \y  (non  figs.  2  and  3),  but  a  comparison  with 
specimens  made  me  doubt  the  correctness  of  the  identification.  I  have 
been  able  to  examine  a  large  series  of  P.  newherryi  from  Bagdad,  near 
Medina,  Bm-bank,  and  other  localities  in  the  Cuyahoga  shale,  in  Medina 
County.  It  is  perhaps  the  most  abundant  form  at  these  localities  next  to 
Chonetes  illinoisensis  f  and  Hall's  figure  seems  to  me  quite  misleading  in 
regard  to  the  surface  ornamentation.     The  figures  show  numerous  close-set 

'Figs.  2  and  3  of  this  species  seem  to  be  dififerent  from  P.  newberri/i.  The  surface  ornamentation 
does  not  appear,  but  it  is  a  much  more  profoundly  arched  shell,  and  comes  from  a  diB'erent  geologic 
horizon. 


532     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

spine  bases  shaped  like  small  rose  thorns,  tapering  at  either  end.  In  the 
specimens  which  I  have  examined  (none  of  them,  it  may  be  noticed,  quite 
attain  the  size  shown  in  the  figure)  the  posterior  portion  alone  presents  this 
appearance,  and  even  there  the  spine  bases  are  so  long  as  to  resemble 
discontinuous  stripe.  They  taper  only  in  one  direction  anteriorly,  and  end 
suddenly  and  acutely,  looking  like  slender  sj^ines,  appressed  or  in  demi- 
relief.  The  termination,  however,  itself  formed  the  base  for  a  small  spine. 
These  ridges  then  are  longer,  more  distant,  and  differenth^  shaped  from  the 
figure.  The  ridges  grow  stronger,  broader,  and  more  continuous  as  the 
shell  increases  in  size,  so  that  the  whole  anterior  margin  is  regularly  and 
strongly  mai'ked  with  spine-bearing  strise,  from  ten  to  twelve  in  10  mm. 
I  do  not  know  the  condition  of  Hall's  types;  but  1  have  noticed  that  in 
localities  such  as  Burbank,  where  the  shell  substance  has  been  leached 
away,  leaving  casts  in  the  sandstone,  these  are  apt  to  show  the  features 
represented  in  the  figure. 

The  surface  ornamentation  of  P.  scabriculus  is  similar  to  that  figured 
for  P.  neivherri/i,  consisting  of  fine,  numerous,  elongated,  spiniferous  pus- 
tules, the  spines  being  situated  near  the  anterior  end;  and  it  is  also  very 
similar  to,  though  somewhat  finer  than,  that  of  P.  papulata  of  the  Hamilton 
group.  This  is,  however,  different  from  the  Waverly  specimens  of  P.  neiv- 
herri/i,  and  the  shape  is  also  different,  being  more  highly  arched,  less  spread- 
ing, and  with  a  more  produced  incurved  beak.  In  shape  and  surface  this 
form  is  very  similar  to  P.  scabriculus  from  the  Carboniferous  of  Glasgow, 
Scotland,  the  chief  difference  arising  from  the  fact  that  in  the  latter  the 
pustules  are  somewhat  more  coarsely  distributed  and  show  conspicuous, 
though  iiTegular,  inequalities  in  size. 

The  dorsal  valve  of  this  species,  as  seen  at  a  different  locality  from  the 
specimen  figured,  when  viewed  from  the  convex  side,  is  crossed  by  numer- 
ous fine  concentric  wrinkles,  and  is  covered  with  fine  pustules,  smaller  and 
juore  closely  arranged  than  those  of  the  other  valve.  The  casts  of  small 
spines  can  be  seen  among  the  pustules  The  ventral  valves  associated  with 
these  are  of  the  normal  type. 

I  have  retained  the  collected  synonymy  of  this  species,  although  I 
doubt  whether  any  of  the  citations  are  really  identical  with  the  form  under 
discussion  or  with  P.  scabriculus.  P  scabriculus,  it  should  be  noticed,  is  in 
Europe  a  Devonian  and  Lower  Carboniferous  form,  while  all  or  nearly  all 


LOWEK  GAKBONIFEKOUS  FOSSILS.  533 

the  citations  in  this  conntry  have  been  from  the  Coal  Measures.  Norwood 
and  Pratten,  however,  have  identified  this  species  from  the  "Mountain  hnie- 
stone"  of  Paris,  Missouri. 

Formation  and  k)cahty:  Madison  Hmestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25,  top 
of  bed  26 ;  J.  P.  Iddings  and  W.  H.  Weed.  North  side  of  north  fork  of  Mill 
Creek,  Snowy  Range;  Louis  V.  Pirsson. 

Productus  gallatinensis  n.  sp. 
PI.  LXVIII,  figs,  lla,  lib,  lie,  lid,  la,  Ih,  Ic. 

Dorsal  valve  not  known.  Ventral  valve  small,  strongly  arched,  the 
curves  on  either  side  of  the  most  elevated  point  being  nearly  alike.  Beak 
small,  rapidly  expanding,  produced,  so  that  the  small  distinct  ears  occur 
about  one-third  the  shell  length  in  front  of  the  apex.  Top  of  the  shell 
broad,  flattened,  but  not  sinuate;  sides  nearly  plain  and  vertical.  The 
width  slightly  exceeds  the  greatest  length,  and  is  about  one  and  one-half 
times  the  height.  The  visceral  region  is  marked  by  numerous  distinct  con- 
centric wrinkles,  and  the  shell  is  ornamented  with  fine,  straight,  radiating  • 
strife  which  bifurcate  on  the  anterior  portion.  A  few  large  spine  bases 
can  be  seen  on  the  anterior  portion  of  the  shell. 

Figs,  la,  Ih,  7c,  of  PI.  LXVIII,  represent  a  form  Avhich  was  at  first 
identified  as  Productella  arcuata  Hall,  but  which  I  now  regard  as  only  a 
variety  of  P.  gallatinensis.  It  is  represented  from  only  one  locality,  the 
top  of  bed  25,  Crowfoot  Ridge,  Gallatin  Range,  and  is  there  found  asso- 
ciated with  true  P.  gallatinensis.  The  shape  is  narrower  and  more  elongate, 
while  the  striae  have  not  the  even,  rigid,  wirelike  appearance  characteristic 
of  the  latter.  It  diff'ers  from  P.  arcuata  in  having  the  strise  finer  and  more 
regular  and  strong. 

The  relations  of  P.  gallatinensis,  P.  parviformis,  and  P.  semireticulatus 
are  close,  and  I  am  almost  disposed  to  regard  them  as  only  varieties  of 
the  same  type.  P.  gallatinensis  is  smaller  than  P.  semireticulatus,  more 
arched,  finer  striated,  narrower,  and  with  more  vertical  sides.  However, 
some  of  the  variations  of  either  type  approach  each  other  closer  than  the 
figured  specimens  would  indicate.  Still  more  nearly  related  to  the  species 
under  discussion  is  P.  parviformis.  In  shape  the  latter  appears  to  be  a 
miniature  reproduction  of  P.  gallatinensis,  but  the  surface  ornamentation  is 
of  about  the  same  fineness. 


534  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Formation  and  locality  :  Madison  limestone,  Limestone  blnff  nortli  of 
Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream ;  Arnold 
Hasrue.  Divide  between  Gallatin  River  and  Panther  Creek,  Gallatin. 
Range ;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  bed  25,  bed  26, 
lower  part  of  bed  27,  upper  part  of  bed  27  ;  J.  P.  Iddings  and  W.  H. 
Weed.  South  of  Forellen  Peak,  Teton  Range ;  S.  L.  Penfield.  Head  of 
Conant  Creek,  Teton  Range ;  W.  H.  Weed. 

Productus  l^vicosta  White. 

PI.  LXIX,  figs.  9«,  9b,  9c. 

Productus  Icvvieostus  White,  1860:  Jour.  Boston  Soc.  Nat.  Hist.,  Vol.  YII,  p.  230. 
(?)  Hall  and  Whitfield,  1877 :  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV,  p.  266, 
PL  V,  figs.  7,  8.  Keyes,  1895:  Geol.  Surv.  Missouri,  Vol.  V,  Ft.  II,  p.  41,  PL 
XXXVIII,  flg.  1. 

This  is  the  type  identified  by  Hall  and  Whitfield  as  P.  Icevicosta  and 
figured  by  them  in  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV,  PI.  V,  figs. 
7,  8.  The  figure  there  given  is  somewhat  restored,  and  in  view  of  new 
material,  which  unquestionably  belongs  to  the  same  species,  appears  to  be 
only  partially  correct.  The  broken  portion  consists  of  the  ears,  which, 
instead  of  being  small  and  inconspicuous,  are  rather  large,  marked  by  the 
same  fine  stx'ise  which  traverse  the  body  of  the  shell,  and  in  addition  by 
strong  longitudinal  wrinkles,  together  with,  in  some  cases,  laumei'ous  spine 
bases. 

This  is  one  of  the  most  common  species  in  the  Yellowstone  National 
Park  and  in  some  localities  is  found  in  great  abundance.  As  there  repre- 
sented it  appears  to  answer  White's  description  in  every  detail. 

Formation  and  locality:  Madison  limestone,  White  JMountains,  Absa- 
roka Range,  just  below  the  Quadi-ant  quartzite;  T.  A.  Jaggar.  East  side 
of  Gallatin  River,  west  of  Electric  Peak;  divide  between  Gallatin  River 
and  Panther  Creek,  Gallatin  Range;  W.  H.  Weed.  Crowfoot  Ridge,  Gal- 
latin Range,  top  of  bed  5;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  top 
of. bed  26,  lower  part  of  bed  27,  bed  31;  J.  P.  Iddings  and  W.  H.  Weed. 
East  slope  of  Survey  Peak,  Teton  Range;  S.  L.  Penfield.  Summit  of 
peak  west  of  Antler  Peak,  Gallatin  Range;  south  slope  of  same;  J.  P. 
Iddings.  North  of  Bighorn  Pass,  Gallatin  Range;  A.  C.  Gill.  Head  of 
Conant  Creek,  Teton  Range;  W.  H.  Weed.  Kinderhook  age,  Bui'lington, 
Iowa;  Louisiana,  Missouri;  Oquirrh  Mountains,  Utah. 


LOWER  (JAUBONIFEliOUS  FOSSILS.  535 

PudniTCTUs  sEMiKETicuLATUs  Martin. 
IM.  LXIX,  figs.  8a,  86,  8c,  8<7. 

Atiomites  scmircticulaiits  Maitiii,  1809:  Petrefacta  Derbieiisia,  p.  7,  PI.  XXXII,  figs. 
1,  2;  PL  XXXIH,  lig.  4. 

Product  lis  semiretivulatiis  Norwood  and  Pratteii,  1854:  Jour.  Acad.  Nat.  Sci.,  2d  series, 
Vol.  Ill,  p.  11.  Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  G37.  Meek,  1872: 
Final  Kept.  U.  S.  Geol.  Surv.  Nebraska,  p.  ICO,  PI.  V,  figs,  la,  Ih.  White,  1875: 
Wheeler's  Expl.  Surv.  W.  100th  Merid.,  Vol.  IV,  p.  Ill,  PI.  VIII,  fig.  1.  Meek 
1877:  King's  l^.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV,  p.  69,  PI.  VII,  fig.  5.  Hall 
and  Whitfield,  1877:  ibid.,  p.  2(i7,  PI.  V,  figs.  5,  0.  Dawson,  1878:  Acadian 
Geol.,  3d  ed.,  p.  296,  fig.  97.  White,  1884:  Thirteenth  Kept.  State  Geologist 
Indiana,  p.  125,  PI.  XXIV,  figs.  1-3.  Herrick,  1885:  Bull.  Denison  Univ.,  VoL 
III,  p.  31,  PI.  I,  fig.  26;  PI.  Ill,  fig.  24;  PI.  VII,  fig.  11;  PI.  X,  fig.  6.  Hall  and 
Clarke,  1892:  Pal.  New  York,  Vol.  VIII,  Pt.  I,  PI.  XVIIa,  figs.  16-18;  PI. XVIII, 
figs.  11-13;  PI.  XIX,  figs.  19-23.  Keyes,  1895:  Geol.  Surv.  Missouri,  p.  50,  PI. 
XXXVI,  fig.  4. 

The  specimens  assembled  under  this  name  come  from  a  number  of 
localities  and  present  considerable  variation.  Taken  as  a  whole,  the  size 
is  smaller  and  the  beak  more  attenuated  than  specimens  from  the  .Coal 
Measures  often  show.  The  median  sinus,  which  often  constitutes  a  marked 
character  in  those  forms,  is  either  indistinct  or  not  developed  at  all,  while 
the  concentric  wrinkles,  which  produce  along  the  striae  the  characteristic 
reticidate  appearance,  are  less  strongly  marked  and  are  confined  to  a  more 
limited  area. 

The  ventral  valve  figured  (PI.  LXIX,  figs.  8ffi,  86,  8c)  is  distinctly  more 
coarsely  striate  than  other  individuals  from  the  same  locality,  while  material 
from  other  localities  is  more  finely  striate  still.  The  figured  .specimen  has 
about  ten  striae  in  10  mm.  along  the  margin,  while  others,  perhaps  the 
greater  number,  have  about  fifteen.  Again,  the  dorsal  valve  (fig.  M)  is, 
though  quite  large,  nearly  flat  over  its  entire  area.  This  specimen  has  a 
transverse  diameter  of  about  33  mm.,  while  other  indi^^duals,  only  23  mm. 
across,  already  show  a  well-marked  geniculation.  These  data  show  about 
the  character  and  range  of  the  variation  observed. 

A  form  identical  with  this  occurs  in  the  Chouteau  limestone  at  Black 
Water,  Saline  County,  Missouri;  Chouteau  Springs,  Cooper  County,  Missouri, 
etc;  and  in  the  Cuyahoga  shale  of  the  Waverly  group  at  Richfield,  Summit 
County;  Bagdad,  Medina  County,  etc.  It  is  closely  related,  perhaps 
identical,  with  P.  flemmgi  var.   huiiingtonensis,  as  identified  by  Hall  and 


53(3     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Whitfield.^  It  differs  in  having  the  sinus  less  strongly  developed,  but  is 
otherwise  indistinguishable.  P.  flemingi  var  hurUnrjtonensis  of  the  West, 
however,  differs  from  the  true  type  seen  at  Burlington,  Iowa,  by  being  more 
coarsely  striate  and  less  distinctly  bilobed.  In  man)'  respects  P.  semireticti- 
latits  of  this  region  resembles  P.  newherryi  var.  annosus  from  the  Waverly 
sandstone  of  Ohio,  but  the  strise  in  the  latter,  as  seen  in  the  figure,  are  more 
angular,  more  irregular,  and  show  a  tendency  to  be  discontinuous. 

Formation  and  locality:  Madison  limestone,  near  summit  of  ridge, 
west  end  of  Hunter  Peak,  Absaroka  Range;  Arnold  Hague.  East  side  of 
Gallatin  River,  west  of  Electric  Peak;  divide  between  Gallatin  River 
and  Panther  Creek,  Gallatin  Range;  east  face  of  Antler  Peak,  Gallatin 
Range;  amphitheater  west  of  Bannock  Peak,  Gallatin  Range,  bed  26;  W. 
H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  2.5;  J.  P.  Iddings 
and  G.  M.  Wright.  Same,  bed  27,  bed  28,  bed  29,  bed  31;  J.  P.  Iddings 
and  W.  H.  Weed.-  South  side  of  Gallatin  Valley,  bed  32;  J.  P.  Iddings. 
NortliAvest  slope  of  Forellen  Peak,  Teton  Range;  S.  L.  Penfield.  Summit 
of  Three  River  Peak,  Gallatin  Range;  J.  P.  Iddings.  Crowfoot  Ridge, 
Gallatiii  Range,  cherty  limestone,  top  of  bed  24;  A.  C.  Gill.  Head  of 
Conant  Creek,  Teton  Range;  W.  H.  AVeed.  Chouteau  limestone.  Black 
Water,  Saline  County,  Missouri;  Chouteau  Springs,  Cooper  County, 
Missouri. 

Productus  parviformis  n.  sp. 

PI.  LXVIII,  figs.  Ca,  Qb,  Gc,  6f7. 

Productus  parvus  White,  1875;  Wheeler's  Bspl.  Surv.  W.  lOOtli  Merid.,  Vol.  IV,  p.  83, 
PI.  V,  figs.  6a,  6d;  uou  P>oductus  parvus  Meek  and  Wortbeu. 

Shell  very  small,  somewhat  wider  than  long.  Surface  ornamented  by 
fine,  even,  radiating  strife,  which  sometimes  exhibit  a  tendency  to  become 
confluent,  as  in  P.  costatus. 

Ventral  valve  deeply  arched,  making  considerably  more  than  a  semi- 
circle ;  front  view  subquadrate,  with  nearly  parallel  sides  and  slightly  curved 
upper  outline.  About  the  beak  are  a  few  deep  concentric  wrinkles,  and  the 
entire  surface  is  crossed  by  fine  concentric  lines.  Occasional  spines  of 
comparatively  large  size  are  scattered  over  the  surface,  especially  near  the 
anterior  margin,  on  the  heavier  compound  plications  when  present. 

'  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol.  IV,  p.  265,  PI.  V,  figs.  9-12. 


LOWER  CAKBONIFEKOUS  FOSSILS.  537 

The  onlv  dorsal  valvo  observed  is  tliat  figured.  It  is  nearly  flat  at 
first,  and  geniculate,  with  well-marked,  somewhat  pointed  ears. 

The  material  from  the  Yellowstone  National  Park  seems  to  be  identical 
with  the  form  identified,  described,  and  figured  by  White  as  Productus parvus 
(loc.  cit.). 

Compared  with  Meek  and  Worthen's  figures  of  that  species,  P.  parvi- 
fonnis  is  seen  to  be  uniformly  smaller,  narrower  in  proportion  to  the  width, 
more  deeply  arched,  and  more  elongate.  It  seems  like  a  miniature  form  of 
P.  (jnllatinensis,  with  which  I  have  at  one  locality  found  it  associated,  and 
of  which,  although  no  intermediate  forms  have  been  observed,  I  am  almost 
disposed  to  regard  it  as  a  variety. 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridg'e,  Gallatin 
Range,  top  of  bed  25 ;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  bed  30,  bed 
31 ;  J.  P.  Iddings  and  W.  H.  Weed.  South  of  Forellen  Peak,  Teton  Range; 
S.  L.  Penfield.     Mountain  Spring,  Nevada. 

CAMAROPHORIA  King,  1846. 

Camarophoria  ringens  Swallow. 

PL  LXIX,  figs.  1«,  lb,  Ic. 

RhynchoneUa  ringens  Swallow,  18G0 :  Trans.  St.  Louis  Acad.  Sci.,  Vol.  I,  p.  653.    Keyea, 

1895:  Geol.  Surv.  Missouri,  Vol.  V,  Pt.  II,  p.  102. 
Camarophoria  ringens  Hall  and  Clarke,  1893 :  Pal.  iSew  York,  Vol.  VIII,  Pt.  II,  p.  214. 
RhynchoneUa  (sp.)  Keyes,  1895:  Geol.  Surv.  Missouri,  Vol.  I,  Pt.II,  PL  XLI,  figs.  8, 11. 

There  is  a  little  doubt  that  the  form  under  discussion  is  identical  with 
that  described  by  Swallow  under  the  name  Bhynchonella  ringens.  His  was 
a  large  shell  (length,  1.90  inches;  breadth,  1.43  inches;  thickness,  0.99 
inch),  triangular  in  outline,  marked  by  about  fourteen  large  plications, 
eight  of  which  were  in  a  broad  shallow  sinus.  More  recently  Keyes  (loc. 
cit.)  cites  the  species  and  says  there  are  twelve  plications. 

The  material  from  the  Yellowstone  National  Park  is  scanty.  Shell 
large,  acuminate-ovate.  Dorsal  valve  flat  on  top,  bending  abruptly  at  the 
sides  and  at  the  front.  Ventral  valve  shallow.  Beak  long,  sharp,  not  much 
incurved,  apparently  pierced  by  a  triangular  or  oval  foramen,  without 
deltidial  covering.  The  surface  is  marked  by  twelve  or  fourteen  large 
but  somewhat  lax,  rounded  plications,  two  or  three  of  which  on  the 
lateral  slopes  are  not  very  distinct.     Two  or  three  plications  are  on  the  fold, 


538     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

tliougli  the  exact  number  is  difficult  to  ascertain,  as  that  feature  is  ahnost 
obsolete. 

If  this  is  not  Bhynchonella  ringens  of  Swallow  it  must  be  a  new  form, 
for  there  is  no  other  representative  of  the  genus  with  which  it  could  be 
confused.  C.  suhtrigona  Meek  and  Worthen,  the  nearest  form,  is  yet  con- 
siderably different.  However,  if  this  reference  is  correct,  Swallow's  spec- 
imen may  have  been  abnormal  in  having  so  many  plications  on  the  fold, 
as  it  is  certainly  a  larger  and  more  -nature  individual. 

In  any  case  the  stratigraphic  value  of  this  species  remains  imaltered, 
for  I  can  vouch  for  the  identity  of  the  Yellowstone  National  Park  material 
with  a  form  from  the  lower  Burlington  chert  of  Louisiana,  Missouri,  which 
passes  among  local  collectors  as  R.  ringens. 

B.  ringens  was  described  from  the  chert  beds  of  the  Encrinital  limestone 
of  Callaway  County.  Swallow  (loc.  cit.)  cites  the  species  from  the  Burling- 
ton of  Callaway  and  Marion  counties,  Avhile  two  forms,  illustrated  by 
PI.  XLI,  tigs.  Ha,  8b,  and  11  (Geol.  Surv.  Missouri,  Vol.  V,  Pt.  II),  prob- 
ably referable  to  C.  ringens,  were  found,  the  one  in  the  Burlington  hmestone, 
the  other  in  the  Kinderhook  shales. 

Formation  and  locality:  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  25;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  bed  28; 
J.  P.  Iddings  and  W.  H.  Weed.  Keokuk  age,  Callaway  County,  Missouri. 
Burlington  age,  Callaway  and  Marion  counties,  Missouri.  Kinderhook 
shales,  Missouri. 

CAMAROTCECHIA  Hall,  1893. 

The  following  species  occur  in  the  lower  divisions  of  the  Madison 
limestone.  They  have  been  referred  to  Hall  and  Clarke's  genus,  Camaro- 
toechia,  although  the  generic  characters  have  not  been  ascertained  in 
detail.  Yet  a  process  of  exclusion  makes  it  very  probable  that  this  refer- 
ence is  correct. 

All  the  shells  have  a  strong  median  septum  in  the  dorsal  valve,  while 
the  ventral  valve  is  aseptate,  but  with  two  converging  dental  larainpe  in  the 
beak.  These  characters,  together  with  their  geologic  position,  form,  natiu-e 
of  fold  and  sinus,  plications,  etc.,  throw  out  most  of  the  other  genera  and 
subgenera  into  which  the  Rhynchonelloid  type  has  been  divided. 


LOWER  CAKBONIFEUOUS  FOSSILS.  539 

Camarotcec'hia  hekrickana  n.  sp. 

PI.  LXIX,  figs.  LV(,  2b,  2r. 

Ventral  \iilvt'  rather  isliallow,  most  prominent  a  little  behind  the  mid- 
dle, flattened  in  front  and  at  the  sides.  Outline  nearly  that  of  a  square. 
Sinus  shallow,  beginning  near  the  middle  of  the  shell;  marked  by  two 
strong-  plications,  on  either  side  of  which  are  tive  or  six  others  slightly  finer. 

Dorsal  valve  considerably  wider  than  long,  sectorifoi-m,  more  gibbous 
than  the  ventral;  sides  reflexed.  Fold  not  very  high,  marked  by  three 
strong  angular  plications.  On  either  side  are  five  plications,  the  more 
lateral  two  smaller  than  the  others. 

This  species  occurs  in  about  the  same  beds  as  C.  metallica,  but  is  sel- 
dom associated  with  it  at  the  same  locahty.  It  is  readily  distinguished 
fi'oni  C.  metallica  by  its  somewhat  large  size,  less  strong  fold  and  sinus, 
and  coarser  and  less  numerous  plications.  Of  these,  C.  metallica  has  live 
on  the  fold  and  eight  on  either  side,  while  G.  Jierrickana  has  but  three  on 
the  fold  and  five  on  each  side. 

Th's  species  has  not  been  observed  with  the  two  valves  in  conjunction, 
but  it  seems  to  have  been  a  much  less  inflated  form. 

It  is  possible  that  this  species  might  correctly  be  referred  to  some  one 
of  the  numerous  Rhynchonellids  described  from  the  Marshall  group  by 
"VVinchell.  I  have  studied  his  descriptions  with  care,  but  none  cover  the 
characters  of  this  form  sufficiently  closely  to  warrant  an  identification  in 
default  of  both  illustrations^  and  identified  material. 

Length  of  a  single  ventral  valve,  10.6  mm.;  width,  12  mm.  Length 
of  a  separate  dorsal  valve,  8.5  nun.;   width,  10.5  mm. 

This  same  form,  or  one  probably  only  A^arietally  distinct  from  it,  is 
found  at  Pellas,  Marion  County,  Iowa. 

Formation  and  locality:  Madison  limestone,  limestone  bluff  north  of 
Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream;  Arnold 
Hague.  Divide  between  Grallatin  River  and  Panther  Creek,  Gallatin  Range; 
amphitheater  east  of  Bannock  Peak,  Gallatin  Range,  bed  28;  W.  H.  Weed. 
Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  26,  upper  part  of  bed  27,  bed 
28;  J.  P.  Iddings  and  W.  H.  Weed.  North  end  of  Teton  Range,  north  of 
Owl  Creek;  W.  H.  Weed.  Chouteau  limestone,  Pellas,  Marion  County, 
Iowa. 


540  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Camarotcechia  metallica  White. 

PI.  LXIX,  flgs.  3a,  3ft,  3c,  3d,  3e. 

Bhynchotiella  metalHca  White,  1874:  Wheeler's  Expl.  aud  Surv.  W.  lOOth  Merid., 
Prelim.  Kept.,  p.  20.  White,  1875:  Ibid.,  Fiual  Kept.,  A^ol.  IV,  p.  129,  PI.  X, 
figs.  10«,  lOd. 

Bhy7ivhonella  pustulosn  (f)  Hall  and  Whitfield,  1877:  King's  U.  S.  Geol.  Expl.  40th 
Par.,  Vol.  IV,  p.  257,  PI.  IV,  ligs,  12-14. 

This  species  was  described  by  White  from  Carboniferous  (Upper  Car- 
boniferous "?)  rocks.  It  was  found  associated,  with  Hemipronites  creiiistria 
and  Spirifer  cameratiis.  My  material  occurs  in  the  lower  beds  of  the  Madi- 
son limestone,  whose  fauna  is  regarded  as  closely  related  to  that  of  the 
Kinderhook  period.  As  far  as  is  shown  by  a  careful  comparison  with  the 
type  specimen,  this  Waverly  form  is  identical  with  White's  species,  and 
were  the  latter  of  more  nearly  the  same  age  I  should  consider  the  reference 
unquestionable.  As  has  been  said,  BhynchoneUa  metallica  was  described 
from  Old  Potosi  mine,  and  H.  crenistria  and  S.  cameratus  are  cited  from  the 
same  locality. 

Spirifer  cameratus  is  closely  related  to  S.  striatus,  and  has  sometimes 
been  mistaken  for  it,  while  almost  any  Lower  Carboniferous  Orthothetes  or 
Derbya  might  pass  as  Hemipronites  crenistria.  Therefore,  it  is  not  impossi- 
ble that  B.  metallica  was  derived  from  lower  strata  than  White  supposed. 

It  is  also  more  than  probable  that  B.  metallica  is  another  representative 
of  the  genus  Camarotcechia,  which  fact  is  not  without  some  stratigraphic 
bearing,  as  Camarotcechia  is  not  known  in  Upper  Carboniferous  rocks,  nor 
indeed  as  yet  above  the  Waverly. 

The  form  here  under  discussion  is  the  same  as  that  described  and  figured 
as  B.  pustulosa  (f)  by  Hall  and  Whitfield,  in  King's  U.  S.  Geol.  Expl.  40th 
Par.,  Vol.  IV,  p.  257,  PI.  IV,  figs.  12-14,  Avhere  it  is  cited  from  Waverly  rocks. 
The  material  from  Yellowstone  National  Park,  though  scanty  from  any  one 
place,  the  localities  being  numerous,  aggregates  a  number  of  specimens 
which  agree  with  one  another  and  exactly  with  B.  pustulosa  (f)  Hall  and 
Whitfield;  but  all  are  without  the  punctate  shell  structure  characteristic  of 
true  Bliynclwpora  pustulosa.  C.  metallica  is  also  much  smaller  than  mature 
B.  pustulosa.,  with  thinner,  sharper,  and  finer  plications.  These,  as  stated 
by  Hall  and  Whitfield,  are  more  numei'ous  than  in  jR.  pustulosa,  and  five  of 
them  instead  of  four  (as  in  the  latter)  regularly  surmount  the  fold. 


LOWER  CAKBONiFEEOUS  FOSSILS.  541 

This  same  shell  is  found  in  the  Chouteau  limestone  of  Cooper  County, 
Missouri,  and  at  the  base  of  the  Lower  Carboniferous  at  Providence  Land- 
ing, Missouri,  and  at  BlaclcAvater  Bridge,  Saline  Comity,  Missouri 

Formation  and  locality  :  Madis.on  limestone.  Hunter  Peak,  Absaroka 
Rano-e :  Arnold  Hay-ue.  Limestone  bluff  north  of  Little  Sunhght  Creek, 
Absaroka  Range;  Arnold  Hague.  East  side  of  Gallatin  River,  west  of 
Electric  Peak;  divide  between  Gallatin  River  and  Panther  Creek,  Gallatin 
Range;  amphitheatre  east  of  Bannock  Peak,  Gallatin  Range,  bed  28; 
W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25 ;  J.  P.  Idduigs 
and  G.  M.  Wright.  Same,  bed  26  ;  J.  P.  Iddings  and  W.  H.  Weed.  South 
of  Forellen  Peak,  Teton  Range  ;  S.  L.  Penfield.  Northwest  slope  of  same ; 
S.  L.  Penfield.  South  slope  of  Quadrant  Mountain,  Gallatin  Range ;  north 
of  Bighorn  Pass,  Gallatin  Range;  Crowfoot  Ridge,  Gallatin  Range,  bed 
24;  A.  C.  Gill.  Same,  top  of  bed  24;  J.  P.  Iddings.  Head  of  Conant  Creek, 
Teton  Range;  W.  H.  Weed.  North  of  Owl  Creek,  northeast  slope  of  Teton 
Range;  W.  H.  Weed.  Upper  Carboniferous,  Lincoln  County,  Nevada. 
Waverly  age,  Wasatch  Range,  Utah.  Chouteau  limestone.  Cooper 
County,  Missouri;  Providence  Landing,  Missouri;  Blackwatei-  Bridge, 
Saline  County,  Missouri. 

Camarotcechia  SAPPHO  Hall  (!). 

Rhynclionella  sappho  Hall,  1860:  Thirteenth  Kept.  New  York  State  Cab.  Nat.  Hist., 

p.  87.    Herrick,  1888:  Bull.  Deuisoii  University,  Vol.  Ill,  p.  40,  PL  V,  tig.  1; 

PI.  Vll,  fig.  23.    Herrick,  1895:  Geol.  Ohio,  Vol.  VII,  PI.  XXI,  fig.  1. 
Ehynchonella  (meiiocesma),  sappho  Hall  1867:    Pal.  New  York,  Vol.  IV.,  p.  340,  PI. 

LIV,  figs.  33-43. 
Camarotcechia  sappho  Hall  and  Clarke,  1893 :  Pal.  New  York,  Vol.  VIII,  Pt.  II,  p.  192. 

PL  LVII,  figs.  10-14. 

The  specimen  which  represents  this  type  is  larger  than  any  in  the 
collection  referred  to  the  genus  Camarotcechia.  When  perfect  it  must  have 
measured  16  mm.  in  length  by  21.5  mm.  in  width.  It  is  a  rather  flat, 
explanate  shell,  resembling  in  this  respect  C.  herrickana  rather  than  the 
other  forms  represented  in  the  Yellowstone  National  Park.  The  lateral 
slopes  are  nearly  straight  or  slightly  concave,  and  extend  about  half  the 
entire  length  of  the  shell,  where  they  are  met  by  the  deeply  bowed  anterior 
margin.  The  fold  is  not  high,  biit  can  be  traced  to  the  rostral  region.  It 
is  traversed  by  six  small,  rounded  plications,  and  about  seven  others  are  to 


542  GEOLOGY  OF  THE   YELLOWSTONE  NATIONAL  PARK. 

be  found  on  each  of  the  sides.  In  every  respect  this  very  closely  resembles 
Hall's  species,  although  onl}'  a  provisional  reference  is  possible,  owing  to 
insufficient  material.  C.  sapplio  first  makes  its  appearance  in  beds  of  the 
Mareellus  period,  but  is  known  to  extend  up  into  the  upper  Waverly 
(Herrick,  1888,  loc.  cit.,  p.  40). 

Formation  and  locality :  Madison  limestone,  Liinestone  bluff  south 
side  of  Soda  Bixtte  Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range ; 
J.  P.  Iddings.  Mareellus  to  Waverly,  Leroy,  Greneseo,  and  York,  New 
York ;  Licking  County,  Ohio. 

Camarotcechia  camarifera  Winchell  (?). 

Bhynchonella  camarifera  Winchell  (A.),  1862 :  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  408. 

This  species  is  represented  in  a  somewhat  fragmentary  manner,  and 
the  material  is  too  poor  for  illustration.  It  resembles  G.  herrickana,  but  at 
the  same  time  seems  to  be  specifically  distinct  from  it.  Shape  ovate ; 
length  equal  to  or  slightly  exceeding  the  width ;  convexity  jnoderate. 
Sides  straight,  meeting  at  the  beak  in  something  less  than  a  right  angle; 
front  deeply  rounded.  Plications  rounded,  four  on  the  fold  and  thi-ee  in 
the  sinus,  with  five  or  six  on  the  sides.  The  plications  are  nearly  straight 
and  not  verj-  divergent,  which  makes  the  shell  look  longer  than  it  really  is. 
It  can  be  distinguished  from  C.  herrickana  by  the  somewhat  different 
arrangement  of  plications  on  fold  and  sides.  The  proportions  of  the  shell 
are  also  different.  The  plications  are  slightly  finer,  less  angular,  and  not 
so  strongly  outcurved  at  their  extremities.  The  nearest  described  species 
which  I  have  found  is  C.  camarifera  of  Winchell. 

Length,  10  mm.;  width,  9.5  ram. 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  bed  26,  bed  28,  bed  30;  J.  P.  Iddings  and  W.  H.  Weed.  Marshall 
group.  Point  aux  Barques,  Michigan. 

Camarotcechia  sp. 
PI.  LXIX,  figs.  4a,  46. 

This  species  is  represented  by  a  single  specimen,  which  seems  to  be 
distinct  from  any  type  occurring  in  the  collection  from  the  Yellowstone 
National  Park.     It  was  found  at  the  limestone  bluff  on  the  south  side  of 


LOVVKH  CxVUBONlFEROUS  FOSSILS.  543 

of  Soda  Butte  Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range,  a 
locality  wliioli  has  already  t'nrnished  several  new  species,  and  seems  to 
possess  a  somewhat  distinct  local  fauna. 

Caniarofa'chia  sp.  consists  of  a  single  dorsal  valve.  The  shape  is 
slightly  itval,  length  and  width  about  equal;  cui'vature  of  the  outline  regu- 
lar, and  not  angular  where  the  anterior  margin  meets  the  lateral  slopes. 
Extremel}'  gibbous,  the  thickness  of  the  valve  being  more  than  half  the 
length  or  width.  Fold  not  very  high,  but  defined  to  the  -sncinity  of  the 
beaks.  It  is  marked  by  five  rounded  plications,  and  a  like  number  are  to 
be  found  on  the  two  sides. 

This  form  seems  to  be  related  to  C.  orbicularis,  of  Chemung  age. 

Formation  and  locality:  Madison  limestone,  limestone  bluff  south 
side  of  Soda  Butte  Creek,  northwest  of  Abiathar  Peak,  Absaroka  Range; 
J.  P.  Iddings. 

LIORHYNCHUS  Hall,  1860. 

LlORHYNCHUS   HAGUEI   n.  sp. 

PI.  LXIX,  figs.  5a,  5b. 

Shell  rather  large,  tumid.  Ventral  valve  fiat  in  effect ;  subquadrate  in 
outline ;  beak  strongly  incurved ;  fold  deep.  Thus  the  anterior  and  posterior 
angles  of  the  quadi-ate  shell  are  strongly  flexed  in  one  direction,  while  the 
lateral  angles  are  prominently  elevated.  Dorsal  valve  very  rotund ;  fold 
high  ;  sides  strongly  recurved.  The  surface  is  smooth  (?),  sometimes  show- 
ing varices  of  growth.  Fold  and  sinus  alone  plicate.  Strife  on  the  sides 
of  the  shell  entirely  obsolete.  There  are  five  plications  on  the  fold,  neither 
sharp  nor  strong.  The  central  three  are  slightly  larger  than  the  lateral 
ones,  which  are  not  defined  on  the  outer  side,  but  lie  in  the  regular  curva- 
ture of  the  shell.     Four  nearly  obsolete  plications  in  the  sinus. 

The  general  appearance  of  the  shell  suggests  the  genus  Pugnax,  but  a 
reference  to  that  type  is  impossible  by  reason  of  internal  structures.  A 
section  across  both  valves  near  the  beak  shows  that  the  dorsal  valve  is 
provided  with  a  well-developed  median  septum,  and  that  the  ventral  valve 
has  two  converging  laminar  plates  in  the  rostral  region. 

Liorhynchus  Jiaguei  is  very  close  to  L.  greenianum  Ulrich,  of  Keokuk  (?) 
age,  from  New  Albany,  Indiana,  but  the  latter  has  three  coarse  plications 


544     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK, 

on  the  fold,  while  the  former  regularly  has  five  fine  ones.  L.  haguei  also 
resembles  to  a  certain  extent  L.  kelloggi  of  the  Hamilton  group,  but  it  is 
more  gibbous,  with  a  higher  fold,  while  the  latter  has,  as  a  rule,  six  to  ten 
plications  on  fold  and  sinus,  with  five  or  six  faint  lateral  plications. 

Comparison  can  also  be  made  with  Liorhynchus  (Pugnaxf)  striatocostatum 
Meek  and  Worthen,  which  has  tlu-ee  or  four  plications  on  the  fold  and  two 
or  thi-ee  nearly  obsolete  ones  on  either  side.  The  fold  is  lower,  broader, 
and  more  quadi-ate,  and  the  plications  surmounting  it  are  much  coarser, 
than  in  L.  haguei,  which  has  the  lateral  plications  either  entirely  lacking 
or  more  indistinct.  The  latter  appears  also  to  be  without  the  fine  striate 
surface  ornamentation  of  Meek  and  Worthen's  species. 

Formation  and  locality  :  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range;  cherty  limestone,  top  of  bed  24;  A.  C.  Gill. 

DIELASMA  King,  18.59. 

DiELASMA  UTAH  Hall  and  Whitfield. 

PI.  LXIX,  figs.  6a,  6b,  6c. 

Terebratula  utah  Hall  and  Whitfield,  1877 :  King's  Geol.  Expl.  40tli  Par.,  Vol.  IV, 
p.  258,  PI.  IV,  fig.  18. 

The  type  of  this  species  is  a  dorsal  valve,  with  a  pentagonal  outline 
and  a  punctate  shell.  The  rectilinear  outline  is  not  constant,  however,  for, 
on  a  block  of  limestone  from  the  same  locality  containing  other  type  mate- 
rial (Athyris  planosulcata  f),  is  a  second  specimen  whose  outline  is  regularly 

cuiwed. 

The  material  from  the  Yellowstone  National  Park  agrees  with  the  above 
so  perfectly  in  general  form,  proportion,  size,  etc.,  that  I  am  confident  both 
belong  to  the  same  species. 

Although  it  has  not  been  possible  to  determine  the  internal  charac- 
ters of  this  form,  it  has  been  referred  to  the  genus  Dielasma  because  of  its 
geological  position,  punctate  shell,  and  characteristic  shape  of  the  ventral 

valve. 

Dielasma  utah  very  closely  resembles  D.  formosum  Hall,  which  occurs 
in' the  Mississippi  Valley,  in  strata  of  Keokuk  age;  but  D.  utah  is  found 
in  the  lower  beds  of  the  Madison  limestones. 


LOWER  CAHBONIFEKOUS  FOSSILS,  545 

l)i('l<i.siii(i  niirh'iji  Hall  iuid  Cliirke'  (iion  Worthcn)  and  Trrchratiihi, 
gorhyl  S.  A.  Miller'-  are  closely  ndated  tbrnus,  but  I  have  not  been  able  to 
examine  tlifem  personally. 

It  is  probable  tliat  7>.  utah  will  prove  synonymous  with  I).  hiirHiif/- 
tonense  White,  of  the  same  geologic  horizon,  but  the  scanty  material  of  the 
former  species,  joined  to  the  very  inadequate  description  of  the  latter,  ren- 
ders it  impossible  to  determine  this  point. 

Specimens  of  D.  hiirliufiioiicnse  White  from  the  Cuyahoga  shale  as 
exposed  at  various  points  in  Summit  and  Medina  counties  can  not  be 
distinguished  from  I),  nfali  by  any  characters  that  I  have  been  able  to 
discover. 

Formation  and  locality:  Madison  limestone,  limestone  bluff  north 
of  Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream ; 
Arnold  Hague.  East  side  of  Gallatin  River,  west  of  Electric  Peak ;  Crow- 
foot Ridge,  Gallatin  Range,  bed  28 ;  J.  P.  Iddings  and  W.  H.  Weed. 
Lower  Cai'boniferous,  Cottonwood  Divide,  Wasatch  Range,  Utah. 

SPIRIFERINA  d'Orbigny,  1828. 

Spiriferina  solidirostris  White. 

PI.  LXXI,  fig.  10«. 

Spirifer  solidirostris  White,  1800:  Jour.  Boston  Soc.  iSTat.  Hist.,  Vol.  VII,  p.  232. 
Spiriferina  solidirostris  White,  1862:  Proc.  Boston  Soc.  ISTat.  Hist.,  Vol.  IX,  p.  24.     A. 
Winchell,  1865:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  120. 

This  is  not  a  common  species  in  the  Yellowstone  National  Park.  It 
has  been  observed  at  a  number  of  localities,  but  is  represented  by  only  one 
or  two  specimens  at  each.  These  correspond  so  entirely  with  S.  solidirostris, 
as  far  as  characters  are  indicated,  that  I  refer  them  very  confidently  to 
White's  species.  The  area,  shape  of  shell,  number  and  character  of 
plications,  and  surface  ornamentation  are  exactly  as  White  has  described 
them.  The  lai-gest  specimen,  a  ventral  valve  of  unusual  size,  measured 
2L5  mm.  in  width  by  12.5  mm.  in  length;  but  the  one  figured  (PI.  LXXI, 
fig.  lOffl),  which  measures  15  ram.  in  width  by  12  mm.  in  length,  is  perhaps 
nearer  the  average. 

1  Hall  and  Clarke,  1895:  Pal.  Now  York,  Vol.  VIII,  Pt.  II,  PI.  LXXXI,  figs.  27,  28. 

-S.  A.  Miller,  1892  (for  1891) :  Seventueuth  Rept.  State  Geologist  Indiana,  p.  687,  PI.  XIII,  figs.  3, 4. 

MON  XXXir,  PT  IT 35 


546  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  ideutitications  of  this  species  are  usually  iucorrect,  the  current  type 
of  specimens  differing-  markedly  from  the  original  description,  which  is 
appended  below.  <S'.  solidirostris  Herrick^  is  an  example  of  tins,  and  the 
form  he  has  figured  can  not  be  included  with  A¥hite's  type. 

"  Shell  rather  small,  nearly  semicircular,  wider  than  long,  widest  at 
the  hinge  line,  where  it  is  sometimes  extended  into  submucronate  points, 
rounded  in  front. 

Dorsal  valve  more  convex  from  beak  to  front  than  transversely.  Beak 
scarcely  prominent,  slightly  projecting  beyond  the  hinge  line. 

Ventral  valve  about  twice  as  deep  as  the  opposite  one,  regularly 
arcuate  from  beak  to  front,  but  a  little  depressed  near  the  cardinal  extremi- 
ties. Area  large  and  well  defined,  foramen  narrow,  beak  acute,  incurved, 
and  becoming  solidified  as  the  foramen  is  progressively  closed.  Dental 
plates  strong,  projecting  a  little  forward  of  the  hinge  line.  From  six  to 
eight  prominent  plications  on  each  side  of  the  mesial  fold  and  sinus,  which 
decrease  regularly  in  size  toward  the  hinge  extremities.  Sinus  rather 
broad  and  deep,  distinctly  defined  even  to  the  point  of  the  beak.  A 
slightly  elevated  ridge  extends  along  its  bottom,  and  a  corresponding 
depression  along  the  mesial  fold. 

Mesial  fold  prominent  and  widely  separated  from  the  plications. 
Surface  marked  by  fine,  lamellose,  concentric  striae,  which  arch  upon  the 
plications  and  the  ridg^e  in  the  mesial  sinus,  and  doubl}'  arch  upon  the 
mesial  fold." 

White's  reference  of  the  species  to  Spiriferina.  is  undoubtedly  correct. 
Shells  from  the  Madison  limestone  show  the  characteristic  finely  punctate 
structure. 

Formation  and  locality:  Madison  limestone,  east  side  of  Grallatin  River, 
west  of  Electric  Peak ;  George  M.  Wright.  Divide  between  Gallatin  River 
and  Panther  Creek,  Gallatin  Range ;  amphitheater  east  of  Bannock  Peak, 
Gallatin  Range,  bed  28  ;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range, 
bed  26,  bed  27,  bed  31 ;  J.  P.  Iddings  and  W.  H.  Weed.  South  of  Forellen 
Peak,  Teton  Range  ;  S.  L.  Peniield.  West  of  Antler  Peak,  Gallatin  Range; 
Antler  Peak,  Gallatin  Range ;  A.  C.  Gill.  Summit  of  peak  west  of  Antler 
Peak,  Gallatin  Range ;  J.  P.  Iddings.     South  slope  of  Quadrant  Mountain, 


'Herrick,  1888:  Bull.  Denlson   University,  Vol.  Ill,  p.  47,  PI.  II,  figs.  9-11;  PI.  V,  fig.  13;  also 
Geol.  Ohio,  Vol.  VII,  PI.  XXI,  tig.  13. 


LOWER  GAltBO^'lFEKOUS  FOSSILS.  547 

Gallatin  Hauo-e :  north  of  Hijiliorn  Pass,  Gallatin  Range;  A.  C.  Gill. 
ClitTty  belt,  Biyliorn  Pass,  Gallatin  Kange ;  J.  P.  Iddings.  Crowfoot 
Ridge,  Gallatin  Range,  lied  24 ;  A.  C.  Gill.  North  of  Owl  Creek,  northeast 
slope  of  Teton  Range ;  W.  H.  Weed.  North  side  of  sonth  fork  of  Will 
Creek,  Snow}  Range;  Louis  X.  Pirsson.  Slide,  east  side  of  Gallatin 
River,  below  Fan  ('reek.  Kinderhook  age,  Burlington,  Iowa;  Hamburg, 
Illinois ;   Sciotoville,  ( )hio. 

SPIRIFER  Sowerby,  1815. 

Spirifer  centronatus  Winchell. 
PI.  LXX,  flgs.  ?,a,  3b,  3c,  3(1. 

Sjyirifer  centronatus  Winchell  (A.),  1865:  Proc.  Acad.  Xat.  Sci.  Philadelphia,  p.  118. 

White,  1875:  Wheeler's  Expl.  Surv.  W.  100th  Merid.,  Vol.  IV,  p.  86,  PI.  V, 

figs.  8a-8c. 
Spirifera  centronata  Hall  and  Whitfield,  1877:  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol. 

IV,  p.  254,  PI.  IV,  tigs.  5,  6. 

Spirifer  centronatus  is  by  far  the  most  abundant  and  universal  form  in 
the  Yellowstone  National  Park.  It  has  been  identified  at  nearly  every 
locality  from  which  collections  have  been  made,  and  appears  often  to  have 
been  present  in  large  numbers.  The  species  is  already  known  in  the  Rocky 
Mountain  region  from  the  reports  of  C.  A.  White  and  of  Hall  and  Whit- 
field. I  have  compared  my  material  with  their  types,  and  also  with  specimens 
from  the  Waverly  rocks  of  Richfield,  Ohio,  and  all  are  without  doubt 
specifically  identical. 

Spirifer  centronatus  usually  develops  four  equal  plications  on  the  fold 
and  three  in  the  sinus,  with  sixteen  or  more  (usually)  simple  plications  on 
the  wings.  The  hinge  line  is  always  the  widest  portion  of  the  shell.  The 
anterior  outline  is  curved,  with  a  tendency  to  become  quadrate.  In  other 
Avords,  the  shape  is  sometimes  that  of  the  smaller  segment  of  a  circle, 
sometimes  more  tumid  below,  with  angular  or  mucronate  extension  at  the 
hinge  line.  Always  transverse.  Area  of  the  ventral  valve  not  very  broad; 
beak  incurved,  small.  Sinus  beginning-  at  the  extremity  of  the  beak.  It  is 
there  relatively  deep,  and  sharply  defined  on  either  side  by  a  prominent 
plication,  but  grows  broader  and  shallower,  somewhat  losing  definition 
below.  Subsequently  a  central  rib  develops  in  the  sinus,  and  this  is  at 
about  the  same  time   supplemented  by  two   others,  one  on   either  side. 


548  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

sprung  as  bifurcations  from  the  two  prominent  bounding  ribs.  Thus  there 
are  normally  three  plications  in  the  sinus.  In  addition,  the  shell  is  marked 
by  about  thirty- two  radii,  sixteeu^on  either  side  of  the  sinus,  which  makes 
an  aggregate  of  thirty-seven  plications  for  the  entire  valve.  Usually  at 
maturity  these  are  all  nearly  or  quite  of  a  size.  Sometimes,  however,  the 
two  bounding  ribs  remain  prominent,  while  those  in  the  sinus  are  almost 
undeveloped.  This  constitutes  the  variety  S.  albapinensis,  and  represeiits 
the  condition  of  most  voung  shells.  Bifurcation  is  common  among  the  alar 
ribs,  but  occasionally  a  shell  will  have  nearly  all  its  plications  bifurcate. 

The  area  of  the  dorsal  valve  is  narrow;  beak  small,  inconspicuous. 
There  is  a  low  but  usually  well-marked  fold,  on  which  at  first  are  only  two 
plications.  These  subsequently  bifurcate,  giving  four  plications  on  the  fold 
of  mature  shells.  Bifurcation  is  centrifugal  and  does  not  result  in  the 
foi'mation  of  primarily  equal  ribs.  The  narrower  ridges  are  in  each  case 
toward  the  wings,  while  the  two  original  ribs  remain  central  and  contiguous. 

The  surface  ornamentation  consists  of  tine  radiating  striae,  parallel  to 
and  superimposed  on  tlie  radiating  ribs.  These  are  interrupted  by  a  system 
of  c(incentric  imbricating  lamellte,  as  in  S.  hiplicatus. 

The  chief  deviation  from  the  type  above  described  consists  in  an 
increase  in  the  number  of  strife,  accompanied  by  a  diminution  in  their  size, 
so  that  four  or  iive  striaj  are  found  in  tlie  sinus,  and  twenty  or  more  on  the 
wings. 

I  believe  that  this  species  will  be  found  to  be  synonymous  with  S. 
hiplicatus,  lint  until  proved  I  have  employed  the  name  of  the  better-known 
form. 

Formation  and  locality:  ]\Iadison  limestone,  near  summit  of  ridge,  west 
end  of  Hunter  Peak,  Absaroka  Range;  limestone  bluff  north  of  Little 
Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream;  east  side  of 
Gallatin  River,  west  of  Electric  Peak;  Upper  Gallatin  Valley,  west  of  Big- 
horn Pass;  Arnold  Hague.  Upper  Gallatin  Valley,  divide  between  Galla- 
tin River  and  Panther  Creek,  Gallatin  Range;  east  face  of  Antler  Peak, 
Gallatin  Range ;  saddle  west  of  Antler  Peak,  Gallatin  Range ;  amphitheater 
wesT  of  Bannock  Peak,  Gallatin  Range,  bed  26;  ainphithea,ter  east  of  Ban- 
nock Peak,  Gallatin  Range,  bed  30;  W.  H.  Weed.  Crowfoot  Ridge,  Gal- 
latin Range,  bed  25;  J.  P.  Iddings  and  W.  H.  Weed.  Same,  top  of  bed 
25 ;  J.  P.  Iddings  and  G.  M.  Wright.     Same,  top  of  bed  26,  lower  part  of 


LOVVliU  CAKIiONlFEHOUS  FOSSILS.  540 

hwl  27,  upper  part  of  bed  27,  bed  28,  bed  31;  J.  P.  Iddiiigs  and  W.  11. 
Weed.  Pass  between  Fox  and  Mink  creeks,  west  of  Two  Ocean  Plateau; 
Arnold  Hague.  East  slope  of  Survey  Peak,  Teton  Kange;  south  of  Forel- 
len  Peak,  Teton  Range;  northwest  slope  of  same;  S.  L.  Penfield.  Antler 
Peak,  Gallatin  Range;  west  of  same;  A.  C.  Grill.  Summit  of  peak  west 
of  Antler  Peak,  Gallatin  Range;  south  slope  t>f  same;  summit  of  Three  River 
Peak,  Gallatin  Range;  J.  P.  Iddings.  South  slope  of  Quadrant  Mountain, 
Gallatin  Range:  A.  C.  Gill.  South  base  of  same;  J.  P.  Iddings.  North  of 
Bighorn  Pass,  Gallatin  Range ;  Crowfoot  Ridge,  Gallatin  Range,  bed  24 ; 
A.C.Gill.  Bighorn  Pass,  Gallatin  Range ;  J.  P.  Iddings.  HeadofConant 
Creek,  Teton  Range;  north  end  of  Teton  Range,  north  of  Owl  Creek;  east 
side  of  Lamar  Valley,  mouth  of  Soda  Butte  Creek,  Absaroka  Range; 
W.  H.  Weed.  Limestone  bluff  south  side  of  Soda  Butte  Creek,  north- 
west of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings.  North  side 
of  north  fork  of  Mill  Creek,  Snowy  Range;  J.  P.  Iddings  and  Louis 
V.  Pirsson.  Waverly  age,  Cu5'ahoga  Falls,  Richfield,  Lodi,  Bagdad,  etc., 
Ohio;    Black    Hills,    Dakota;    Wasatch    Range,   Utah;    Mountain    Sjn'iug, 

Nevada. 

Spirifek  centronatus  var.  semifurcatus  n.  var. 

PL  LXX,  fig.  ia. 

This  form  is  related  to  S.  centronatus  and  to  S.  mcsicosfalis,  standing  about 
midwav  between  them.  It  seems  to  me  to  be  sufficiently  out  of  the  rang-e 
of  ordinary  variations  of  S.  centronatus  to  be  described  as  a  distinct  variety. 

It  is  of  the  imbrex  type,  semielliptieal  in  outline,  fold  and  sinus 
strongly  expressed ;  surface  ornamented  with  regular  imbricating  growth 
lines  and  strong  radiating  ribs.  Of  the  latter  there  are  ten  or  eleven  upon 
tlie  wings  and  two  somewhat  larger  ones  upon  the  median  fold.  These, 
however,  show  a  constant  tendency  to  bifurcate,  wliich  often  results  in  tlie 
formation  of  four  plications ;  but  the  median  furrow  of  the  fold  is  stronger 
than  the  two  others.  Length  of  the  dorsal  valve  is  30.5  nun.  transversely; 
longitudinally,  12. .5  mm. 

The  dorsal  shown  by  PI.  LXX,  fig.  4a,  can  be  almost  exactly  mated  in 
size,  in  shape,  and  in  the  number,  size  and  distribution  of  the  plications  bv 
specimens  of  S.  mcsicostaUs.  This,  however,  is  rather  small  for  mesicostalis, 
and  I  have  not  observed,  in  a  large  series  of  this  species,  any  tendency 
toward  bifurcation  in  the  t^vo  plications  on  the  fold.     Compared  with  S. 


550  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

hiplicatus  var.  semifiircatus,  S.  centronatus  has   somewhat  smaller  and  more 

numerous  plications,  and  the  fold,  which  is  perhaps  not  quite  so  elevated, 

is  surmounted  by  four  or  more  equal  radii. 

Formation  and  locality:  Madison  limestone,  Hunter  Peak,  Absaroka 

Range ;  T.  A.  Jaggar.     Near  summit  of  ridge,  west  end  of  Hunter  Peak, 

Absaroka  Range  ;  Arnold  Hague.     Crowfoot  Ridge,  Grallatin  Range,  top  of 

bed  26  ;  J.  P.  Iddings  and  W.  H.  Weed.     Under  Quartzite  Ridge,  north  side 

of  Burnt  Fork. 

Spirifeb  subattenuatus  Hall. 

Spirifer  snbattenuatus  (by  mistake,  Spirifer  suhmucronata)  Hall,  1858:   Geol.  Surv. 

Iowa,  Vol.  I,  Pt.  II,  p.  504,  PI.  IV,  tigs.  3a-3c. 
Spirifer    suhatienuuia    Wiucliell    (A.),  1SG2:    Proc.  Acad.    Nat.    Sci.,    Philadelphia, 

p.  4C5,    Whiteaves,  1891:    Coutributions  to  Canadian  Palieoutology,  Vol.  I, 

p.  223. 

Shell  rather  small,  semicircular,  alar  angles  somewhat  rounded  to  sharp. 
On  either  side  of  the  fold  and  sinus  there  are  eight  to  ten  comparatively 
large  radiating  ribs,  which  are  crossed  by  strong  concentric  imbricating 
ridges.  Very  variable  in  the  number  of  plications  on  fold  and  .sinus.  One 
dorsal  valve  shows  a  low  fold  with  two  strong  radii  equal  to  those  on  the 
wings.  Another  specimen  has  a  rather  high  fold  with  a  very  faint  median 
furrow.  One  ventral  valve,  on  the  other  hand,  shows  a  sharp  median  ridge 
in  the  rather  deep  sinus,  while  still  another  has  the  sinus  simple  for  over 
half  its  length,  when  suddenly  four  low  plications,  somewhat  smaller  than 
the  rest,  appear  in  it.  Length  of  this  last  specimen,  10.5  mm.;  width,  15 
mm.     Another  example  is  considerably  larger  than  this. 

The  form  in  question  seems  to  be  closely  allied  to  8.  centronatus,  from 
some  varieties  of  which  it  is  not  widely  separated.  It  also  bears  some 
resemblance  to  .S'.  strifjostis  Meek  and  S.  an/entarins  Meek,  to  the  latter  in 
point  of  size,  to  the  former  in  the  plications  of  fold  and  sinus.  S.  arrjentarius 
and  S.strk/osiis  are  both  described  from  Devonian  strata;  so  is  S.  subaffenu- 
atiis,  but  it  is  known  to  occur  in  the  Waverly  also.  The  material  studied 
is  unsatisfactory. 

Formation  and  locality:  IMadison  limestone,  Stinkingwater  Valley, 
below  mouth  of  the  canyon,  Absaroka  Range;  Arnold  Hague.  Chemung 
age,  Independence  and  BuflPalo,  Iowa;  Rock  Island,  Illinois;  Naples,  New 
York;   Athabasca    River,    Canada.     Marshall  group.  Point    aux    Barques, 


LOWER  CARBONIFEROUS  FOS8ILS.        .  551 

Spiriker  marionensis  Shuiruinl  (?) 

Spirifer  marionensis  Sliumard,  1855:  Geol.  Kept.  Missouri,  p.  203,  PI.  0,  figs.  Sa-.Sc. 

Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  501,  PI.  VI,  figs.  l«-lc.     Hall 

and  Clarke,  189.-):  Pal.  New  York,  Vol.  VIII,  Pt.  II,  PI.  XXXI,  fig.  lo. 
iSpiri/tra  marioncn.siti  Wiuchell   (A.),  1870:    Proc.  Am.  Phil.  Soc,  Vol.   XI,  p.  2.52. 

Hall,  1883:    Second  Ann.  Kept.  New  York  State  Geologist,  PI.  LVI,  fig.  15. 

Herrick,  1888:  Hull.  Denison  University,  Vol.  Ill,  p.  43,  PI.  VI,  tigs.  2-4;  PI. 

VII,  tig.  11;  Vol.  IV,  p.  2(!,  PI.  II,  tig.  2. 

This  form  is  found  only  at  the  head  of  Couant  Creek,  Teton  Range. 
The  material,  which  is  much  crushed  and  broken,  so  far  as  ascertained,  can 
well  be  referred  to  Shumard's  species.  It  is  much  larg-er  and  more  coarsely 
plicate  than  S.  centronatus,  and  much  resembles  S.  striatns  of  this  report, 
except  that  the  surface  is  crossed  by  numerous  lamellose  concentric  strise, 
whereas  the  other  is  smooth.  A  satisfactory  identification  is  rendered 
impossible  bv  the  character  of  the  material. 

Formation  and  locality:  Madison  limestone,  head  of  Conant  Creek, 
Teton  Range;  W.  H.  Weed.  White  Mountain,  Absaroka  Range,  just  below 
Quadrant  quartzite ;  T.  A.  Jaggar.  Chouteau  age,  Louisiana  and  Hannibal, 
Missouri;  Portsmouth  and  Sciotoville,  Ohio. 

Spikifer  striatus  var.  madisonensis  n.  var. 
PI.  LXX,  figs.  2«,  2&,  2e,  2d. 

This  form  in  general  appearance  resembles  *S'.  striatus  Martin,  of  the 
Mountain  limestone  of  vai'ious  European  localities.  It  does  not  attain 
so  large  a  size  as  is  often  seen  among  specimens  of  S.  striatus,  and  the 
strise  are  coarser  and  less  numerous  than  in  some  of  the  forms  figured  by 
Davidson. 

The  material  under  discussion  approaches  most  closely  to  certain 
specimens  from  Cork,  Ireland,  with  which  it  has  been  compared,  but 
certain  differences  obtain  which  are  worthy  of  at  least  varietal  distinction. 
The  area  in  S.  striatus  var.  madisonensis  is  hig-her,  even  in  specimens  of 
considerably  smaller  size;  the  ventral  beak  more  overhanging,  and  the 
foramen  higher  in  proportion  to  its  width.  The  outline  shape  of  both 
types  is  nearly  the  same,  likewise  the  number  and  size  of  the  striae.  The 
fold  is  somewhat  higher  in  the  Irish  form,  and  considerably  more  angular. 
The  strise  bifurcate  in  the  immediate  vicinity  of  the  beak,  and  often  again 


552  GEOLOGY  OF  THE  YELLOWSTOiSiE  ^^ATIONAL  PARK. 

near  tlie  anterior  margin.  In  the  variety  inadisonensis  the  stria?  bifurcate 
near  the  anterior  margin,  but  can  be  traced  backward  to  then-  origin  at  the 
beak  without  bifurcation.  In  neither  form  are  the  striaj  interrupted  by 
imbricating  lamellae. 

Hall  and  AVhittield  distinguish  two  types  among  the  forms  from  Utah, 
which  tliey  refer  to  S.  striatus.  The  one  which  is  lower  in  the  stratigraphic 
series  is  said  to  be  transversely  elongated,  while  the  higher  one  is  about  as 
long  as  wide,  and  has  finer,  more  angular,  and  more  fasciculate  strife. 
Their  material  is  so  crushed  that  it  is  impossible  to  institute  a  satisfactoi'v 
comparison,  Ijut  if  5.  striatus  var.  madisouensis  is  identical  with  either  of 
these,  it  must  be  with  the  former  (lower)  type.  It  ditfers  distinctlv  from 
the  form  figured  on  PI.  Y,  figs.  13,  14  (loc.  cit.),  which  is  somewhat  larger; 
the  area,  instead  of  being  nearly  straight  and  vertical,  is  deeply  curved,  at 
first  nearly  horizontal,  then  resurgent;  the  fold  is  sudden,  high,  and  thin. 

Spirifer  striatus  var.  madisonensis,  when  mature,  can  be  readily  distin- 
guished from  S.  centronatus,  with  which  it  is  associated.  It  is  much  larger, 
the  fold  and  sinus  less  defined,  plications  more  numerous,  but  less  sharp, 
and  not  covered  with  the  imbricating  concentric  lamellfe  which  well- 
preserved  surfaces  of  S.  centronatus  show. 

The  largest  specimen,  an  incomiDlete  ventral  valve,  measures  55  mm. 
in  breadth.  Another  shell  measures  55  mm.  in  breadth  by  35  mm.  in 
length,  which  is  perhaps  near  the  average.  Young  specimens,  however, 
are  broader  in  proportion  to  their  length,  and  can  scarcely  be  distinguished 
in  shape  from  S.  centronatus  of  the  same  size. 

Formation  and  locality:  Madison  limestone,  Stinkingwater  Valley, 
below  mouth  of  the  canyon,  Aljsaroka  Range;  Arnold  Hague.  Crowfoot 
Ridge,  Gallatin  Range,  cherty  limestone,  top  of  bed  24;  A.  C.  Grill. 

Spirifer  sp. 
PI.  LXX,  fig.  la. 

This  form  is  known  only  from  an  incomplete  dorsal  valve,  but  it  is  so 
striking  that  it  seems  worthy  of  some  notice.  It  is  very  transverse,  the 
width  being  51  mm.  and  the  length  16.5  mm.  Shape  triangular:  trun- 
cate in  front;  wings  acutely  angular,  mucronate  (?).  The  fold  is  unde- 
fined and  scarcely  at  all  raised  above  the  general  curvature  of  the  shell, 
surmounted  by  four  or  fi\-e  bifurcated  plications.     On  either  side  are  found 


LOWER  CARBONIFEROUS  FOSSILS.  553 

about  twenty  other  plications,  which  (on  the  cast)  gradually  become  finer 
and  more  obsolete  until  they  disappear  and  the  extreme  alar  portion  is 
smooth.  I  know  of  no  type  with  which  this  can  aptly  be  compared 
except  S.forbesi,  of  the  Burlington  group. 

Formation  and  locality:  Madison  limestone,  east  slope  of  Survey 
Peak,  Teton  Range;  S.  L.  Penfield. 

Spirifer  sp. 

A  solitary  specimen,  not  referable  to  any  of  the  forms  yet  recognized 
in  the  Yellowstone  National  Park.  It  is  a  large  shell,  probably  when 
complete  not  less  than  63.5  nun.  wide  by  44.5  nun.  long;  a  ventral  valve. 
There  is  a  broad,  shallow  sinus,  which,  together  Avith  the  wings,  appears  to 
be  covered  by  comparatively  fine,  obscure,  radiating  striae.  The  entire 
rostral  cavity  is  filled  Avitli  sliell  deposit,  as  in  S.  pJemis,  of  the  Burlington. 
Externally  this  form  approaches  Syringothyris ;  the  beak  is  erect  and  the 
whole  shell  has  what  may  be  called  a  heraiconical  shape;  but  it  is 
developmentally  not  a  true  species  of  that  genus. 

Formation  and  locality:  Madison  limestone.  Snake  River  Valle}',  west 
of  Two  Ocean  Plateau;  W.  H.  Weed. 

MARTINIA  McCoy,  1844. 

Martinia  rostrata  n.  sp. 

PI.  LXX,  figs.  5rt,  5t,  5c,  5d,  5e,  5/',  5g. 

Athyris  planosulcata  Hall  aud  Whitfield,  1877  (pars) :  Kiug's  U.  S.  Geol.  Exi>l.  40tb 
Par.,  Vol.  IV,  p.  257,  PI.  IV,  tig.  10. 

Shell  large,  obese,  lozenge-shaped;  when  young,  wider  than  long; 
when  old,  length  and  width  about  equal.  Ventral  valve  productiform ; 
beak  prominent,  incurved  over  a  moderate-sized  area.  Foramen  large,  open. 
Hinge  line  half  or  three-fourths  the  Avhole  width  of  the  shell.  Surface 
smooth;  mai'ked  by  a  shallow  sinus  extending  to  the  extremity  of  the  beak, 
whei'e  it  is  defined;  less  marked  below  and  accompanied  by  a  flattening  of 
the  whole  valve.  Dorsal  valve  rounded  behind,  converging  in  front  in 
somewhat  straight  lines,  whose  junction  is  anticipated  by  the  truncation  of 
a  very  low  fold.  Beak  prominent,  but  not  produced.  Transverse  curva- 
ture gentle  and  even,  or  sometimes  formed  by  the  two  planes  of  an  obtuse 
dihedral  angle,  whose  edge  is  the  median  line.     Highest  point  is  at  the  umbo. 


554  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

Mature  specimens  can  scarcely  be  mistaken  for  anytliing  else  in  the 
same  beds.  The  smooth  surface  and  area  with  triangular  foramen  would 
suffice  to  disting'uish  even  young  shells  from  C.  crassicardinalis,  which  they 
most  resemble,  but  when  these  characters  are  obscured  the  prominent  beak 
and  mesial  sulcus  of  the  ventral  valve  are  diagnostic.  There  is  some  simi- 
larity with  Spirifer  (Martinia)  rjlaher  Martin,  to  which  I  believe  this  type 
to  have  been  usually  referred.  The  produced  and  overhanging  beak  and 
large  area  of  M.  rostrata  are  well-marked  specific  characters.  The  fold  and 
sinus  of  M.  r/Jahra  are  stronger  than  the  same  features  of  31.  rostrata,  where, 
in  fact,  they  are  but  slightly  developed,  and  often  exhibit  a  tendency  to 
bifurcate,  manifested  by  a  median  sulcus  and  ridge  of  more  or  less  depth, 
never  seen  in  the  latter. 

The  synonymy  of  this  form  includes,  so  far  as  I  am  aware,  besides  S. 
glaber,  of  various  authors,  only  Atliyris  planosuJcata  {f)  Hall  and  Whitfield 
(non  Phillips),  figured  in  King's  U.  S.  Expl.  40th  Par.,  Vol.  IV,  p.  257,  PI. 
IV,  fig.  10,  which  appears  to  be  a  young  specimen  of  M.  rostrata.  Widtli 
of  large  specimen,  ventral  valve,  38  mm.;  length,  35.5  mm.  Width  of 
medium-sized  specimen,  ventral  valve,  29  mm.;  length,  25.5  mm.  Width 
of  large  specimen,  dorsal  valve,  51  mm.;  length,  34.5  nnn.  Width  of  me- 
dium-sized specimen,  dorsal  valve,  29  mm.;  length,  23.5  mm. 

Formation  and  locality:  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  G.  M.  Wright  Amphitheater  west  of  Bannock 
Peak,  Gallatin  Range,  bed  26;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  25;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  lower 
part  of  bed  27,  bed  31;  J.  P.  Iddings  and  W.  H.  Weed.  South  .side  of 
Gallatin  Valley,  bed  32;  J.  P.  Iddings.  West  of  Antler  Peak,  Gallatin 
Range;  A.  C.  Gill.  South  slope  of  peak  west  of  Antler  Peak,  Gallatin 
Range;  sunmiit  of  Three  River  Peak,  Gallatin  Range;  J.  P.  Iddings.  South 
slope  of  Quadrant  Mountain,  Gallatin  Range;  north  of  Bighorn  Pass,  Gal- 
latin Range;  A.  C.  Gill.  North  of  Owl  Creek,  northeast  slope  of  Teton 
Rano-e;  W.  H.  Weed.  Limestone  Ijluff"  south  side  of  Soda  Butte  Creek, 
northwest  of  Abiathar  Peak,  Absaroka  Range;  J.  P.  Iddings. 


LOWER  CARBONIFEROUS  FOSSILS.  555 

RETICULARIA  McCoy,  1844. 

Reticularia  cooperensis  Swallow. 

PI.  LXX,  figs.  9a,  9fc,  9c. 

Spirifera  cooperensis  Swallow,  18G():  Trans.  St.  Louis  Acad.  Sci.,  Vol.  I,  p.  643.    Keyes, 

1895:  Geol.  Surv.  Missouri,  Vol.  V,  Pt.  II,  p.  78. 
Spiri/er  hirtus  White  and  Whitfield,  1862:  Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  VIII, 

p.  293.     1  Winchell  (A.),  186r.:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  119.    Hall 

and  Clarke,  1895:  Pal.  New  York,  Vol.  VIII,  Pt.  II,  PI.  XXXVIII,  fig.  14 

(?  PI.  LXXXIV,  tigs.  36,  37). 
^Spiri/er  coo2)erensis^leek  and  Wortheu,  1866:  Geol.  Surv.  Illinois,  Vol.  II,  p.  155,  PI. 

XIV,  flg.  5. 

The  specimens  here  referred  to  R.  cooperensis  Swallow  have  been 
compared  with  material  from  the  Chouteau  limestone  of  Cooper  County, 
Missouri,  where  Swallow's  types  were  found.  The  iinusually  perfect  agree- 
ment exhibited  in  the  two  forms  leaves  no  doubt  of  their  specific  identity. 
The  same  form  occurs  in  the  Waverly  at  Richfield,  Ohio. 

Although  Spirifer  cooperensis  Meek  and  Worthen  is  retained  in  the 
synonymy  of  this  species,  I  believe  they  were  dealing  with  a  distinct 
though  similar  form.  It  is  only  about  half  the  size  of  mature  B.  cooperensis, 
and  has  a  distinct  fold  with  three  or  four  plications  on  either  side,  more  as 
in  B.  peculiaris  Shumard.  In  fact,  it  seems  highly  probable  that  they  were 
dealing  with  the  shell  described  by  lialP  from  the  same  (Goniatite)  beds, 
three  years  previously,  as  Spirifer  semipUcatus.  On  account  of  differences 
mentioned  above,  I  believe  this  constitutes  a  distinct  specific  type,  although 
Hall  may  have  included  in  his  description  some  of  Swallow's  species. 

Meek  and  Worthen  seem  to  be  in  error  when  they  state  that  Swallow 
refers  to  his  species  "obscure,  radiating  plications"  (Meek  and  Worthen, 
loc.  cit,  p.  156).  He  does,  indeed,  speak  of  "punctate  and  plicate  folds" 
and  "concentric  folds  marked  with  small  pits  and  short  longitudinal  plica- 
tions," but  this  had  reference  to  the  delicate  longitudinal  flutings  of  the 
laminfe,  due  to  the  spines  or  their  bases  (a  character  shown  in  all  the  speci- 
mens examined)  rather  than  to  the  large  radiating  folds  shown  in  3Ieek 
and  Worthen's  figure. 


'Thirteenth  Rept.  New  York  State  Cab.  Xat.  Hist.,  p.  111. 


556  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

Spirifer  hirtus,  from  the  same  beds  and  the  same  region  as  B.  cooper- 
ensis,  may  ahnost  certainly  be  placed  in  the  synonj^my  of  the  latter  species. 

Foi-mation  and  locality":  Madison  limestone,  east  side  of  Gallatin 
River,  west  of  Electric  Peak;  Upper  Gallatin  Valley,  west  of  Bighorn 
Pass;  Arnold  Hague.  Amphitheater  west  of  Bannock  Peak,  Gallatin 
Range,  bed  26;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of 
bed  25;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  top  of  bed  26,  top  of  bed 
27,  bed  28,  bed  31;  J.  P.  Iddings  and  W.  H.  Weed.  South  of  Forellen 
Peak,  Teton  Range;  S.  L.  Penfield.  South  slope  of  peak  west  of  Antler 
Peak,  Gallatin  Range;  J.  P.  Iddings.  North  of  Bighorn  Pass,  Gallatin 
Range;  A.  C.  Gill.  Head  of  Conant  Creek,  Teton  Range;  W.  H.  Weed. 
Chouteau  age,  Chouteau  Springs,  Missouri;  Rockford,  Indiana;  Burling- 
ton, Iowa;  Hickman  County,  Tennessee;  Richfield,  Bagdad,  etc.,  Ohio. 

Reticularia  cooperensis  var.  . 

PL  LXX,  figs.  C«,  Gh,  6c. 

Spirifera  setigera  Hall  and  Wbitfleld,  1877:  King's  U.  S.  Geol.  Expl.  40tli  Par.,  Vol. 
IV,  p.  270,  PI.  V,  figs.  17,  18. 

This  form  is  once  again  as  large  as  R.  cooperensis,  of  which,  for  the 
present,  I  regard  it  as  a  variety,  but  I  am  not  in  a  position  to  designate 
any  other  character  on  which  a  difterentiation  can  be  made.  The  single 
specimen  found  in  the  collection  stands  out  so  strikingly  from  the  material 
referred  to  B.  cooperensis  that  it  is  significant  of  further  diff'erence,  but  the 
specimen  is  so  exfoliated  and  crushed  that  a  detailed  comparison,  which 
might  bring  out  constant  important  contrasts  in  surface  ornamentation,  etc., 
is  impossible. 

As  far  as  the  limited  material  permits  me  to  judge,  the  same  form 
occurs  in  the  Eureka  district  and  at  Dry  Canyon,  Utah,  where  it  has 
uniformly  been  identified  as  R.  setigera  Hall,  of  the  Chester  limestone, 
which  it  strongly  resembles.  However,  in  the  Yellowstone  National  Park 
it  is  in  the  lower  part  of  the  Carboniferous  series,  associated  with  Waverly 
forms  {R.  cooperensis,  etc.). 

A  comparison  with  specimens  of  R.  setigera  from  Chester,  Illinois, 
shows  that  the  Waverly  form  is  of  about  the  same  size,  but  more  transverse, 
beak  less  incurved,  area  higher  and  larger.  As  has  been  said,  a  comparison 
of  the  surface  ornamentation  of  the  two  forms  is  not  possible. 


LOWER  CARBONIFEROUS  FOSSILS.  557 

Compared  witli  tlu'  Hnrliiifrton  t'oriii,  It.  coopcrens'is  var.  is  smaller,  less 
transverse;    fold  and    sinus  less  pronounced;    area  proportionally  not  so 

broad. 

The  specimen  iigured  is  from  the  Eureka  district,  Nevada.  The 
original  shape  and  pi'oportions  are  better  maintained. 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  25;  J.  P.  Iddings  and  C  M.  Wright.  Lower  Carbon- 
iferous, Eureka  district,  Nevada;   Dry  Canyon,  Utah.. 

Reticularia  (?)  PECULiARis  Sliumard. 
PI.  LXX,  figs.  8fl,  Sh. 

Spirifer  ?  peciiliaris  Shuinard,  1S5.5:  Geol.  Rept.  Missouri,  i>.  202,  PL  0,  figs.  7a,  7h. 
Spirifem  {Maitinia)  peculiaris  White,  1S75:  Wheeler's  Expl.  Surv.  W.  100th  MericL, 
Vol.  IV,  p.  «0,  PI.  V,  tigs.  7a,  7b. 

This  species  is  so  rare  in  the  Yellowstone  National  Park,  and  its 
preservation  is  so  unsatisfactory,  that  any  less  striking  form  could  scarcely 
be  identified. 

It  can  be  distinguished  from  B.  suhrotundata  by  its  larger  and  less 
numerous  plications,  of  which  there  are  only  six  or  seven  on  either  wing, 
while  the  fold  and  sinus  are  simple. 

B.  peadiaris  is  found  in  the  yellow  sandstone  at  Burlington,  Iowa,  and 
in  the  brown  limestone  of  Chouteau  age  at  various  places  in  Missouri. 

I  am  not  confident  that  this  is  con-ectly  referred  to  Eeticulnria.  Exfo- 
liated specimens  from  the  Chouteau  limestone  appear  to  have  possessed  a 
finely  laraellose-spinose  surface. 

Formation  and  locality:  Madison  Hmestone,  summit  of  Three  River 
Peak,  Gallatin  Range;  J.  P.  Iddings.  East  side  of  Lamar  Valley,  mouth 
of  Soda  Butte  Creek,  Absaroka  Range;  W.  H.  Weed.  Kinderhook  age. 
Cooper  County,  Missouri;  Mountain  Spring,  Nevada. 

ReTICULAEIA  (?)    SUBROTUNDATA  Hall. 
PL  LXX,  figs.  7rt,  7h. 

Spirif era  suhrotundata  Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  521,  PI.  VII,  fig.  8. 
Keyes,  1895:  Geol.  Surv.  Missouri,  Vol.  V,  p.  78. 

I  have  this  species  from  a  single  locality  beyond  the  confines  of  the 
Yellowstone  National  Park,  but  associated  with  a  fauna  clearly  identical 
with  that  of  the  Madison  limestone. 


558     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

The  ventral  valve  is  strongly  arched  in  an  antero-lateral  direction, 
somewhat  flattened  transversely,  with  a  broad,  shallow  sinus  which  can  be 
traced  quite  to  the  beak,  losing  distinctness  as  it  grows  broader.  Beak 
high,  strongh^  incurved.  Area  triangular  and  not  well  defined.  Foramen 
large  and  higli.  Surface  marked  by  about  twenty-six  fine,  low  plications, 
about  six  of  which  lie  in  the  sinus,  and  with  about  ten  on  either  wing. 
The  shell  is  superficially  marked  by  iimumerable  fine  pits,  much  resembling 
the  punctation  in  the  genus  Spiriferina,  but  this  character  is  restricted  to  a 
thin  outer  layer,  beneath  which  the  shell  substance  is  fibrous  and  irapunc- 
tate.  This  appearance  is  probably  secondary,  resulting  from  an  originally 
S})inose  exterior,  which,  with  the  general  character  of  the  species,  elongate 
shape  and  obsolescent  plications,  distinguishes  it  from  any  representative 
of  the  genus  Spiriferina,  and  seems  to  denote  an  alliance  witli  Reticularia. 

As  regards  its  specific  position,  a  comparison  with  typical  Spbifcra 
subrotundata  Hall,  from  the  yellow  sandstone  of  Burlington,  Iowa,  leads  me 
to  believe  that  it  is  identical  with  that  species. 

It.  subrotundata  is  in  many  ways  comjjarable  to  B.  jyecidiaris,  but  the 
character  of  the  plications  aff"ords  an  easy  basis  for  discrimination.  B.  sub- 
rotundata  has  finer  and  more  numerous  plications,  of  which  six  or  more  are 
in  the  fold  and  sinus,  while  in  R.  peculiaris  the  fold  and  sinus  are  undivided. 

The  same  form  occurs  in  the  lower  Burlington  of  Pike  County,  Mis- 
souri, and  seems  to  have  been  usually  identified  as  B,.  peculiaris. 

Formation  and  locality:  Madison  limestone,  Little  Belt  Mountains, 
east  side  of  Belt  Creek,  5  nfiles  above  IMonarch,  Montana;  W.  H.  Weed. 
Lower  Burlington  chert,  Pike  County,  Missouri. 

SYRINGOTHYRIS  A.  Winchell,  1863. 

Syringothyris  cakteri  Hall. 

ri.  LXXI,  figs.  1«,  1/a  Ic. 

iSpirifer  carteri  Hall,  1857:  Tenth  Aun.  Rept.  New  York  State  Cab.  Nat.  Hist.,  p.  170. 
(partim)  Meek,  1875:  Pal.  Ohio,  Vol.  II,  p.  285  (not  liis  figures  =  S.  texta  Hall). 

Spirifer  (Cyrlia!')  hannibalensis  Swallow,  1860:  Trans.  St.  Louis  Acad.  Sci.,  \'ol.  I, 
p.  647. 

Syringothyris  typa  Winchell,  1863:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  p.  7.  Winchell, 
1870:  Proc.  Am.  Phil.  Soc,  Vol.  XI,  p.  252.  Hall  and  Clarke,  1893:  Pal.  New 
York,  Vol.  VIII.  Pt.  II,  p.  48,  tig.  40.  Hall  and  Clarke,  1895:  PaL  New  York, 
Vol.  VIII,  Pt.  II,  PI.  XXVI,  tigs.  6,  7, 10;  PI.  XXVII,  figs.  1-3. 


LOWER  CARBONIFEKOUS  FOSSILS.  559 

Spiri/cf  citinjidatKii  iMeek,  ISOf):   i'roc.  Acad.  Nut.  Sui.  riiihulelpliiii.  \ol.  X  VII.  j).  275. 

Meek,  1867:  Am.  Jour.  Sci.,  Vol.  XLVII  (2),  p.  407. 
Spiri/ercunpidalii.sf  Meek,  1S77:  U.  S.  Geol.  Expl.  Jdtli  I'ar.,  \'ol.  IV,  p.  S7,  PI.  Ill,  figs. 

II,  llri  (lion  Martin). 

Sijriitf/otlii/ris  cii.spi(h(ti(s  Walcott,  1884:  Hon.  U.  S.  (leol.  Surv.,  ^'ol.  VIII,  Pal.  Eureka 
District,  p.  219  (iion  Martin).     Uerrick,  1888  (paitiui) :  Bull.  Denison  Univ.,  Vol. 

III,  p.  41,  PI.  I,  lis-.  7;  PI.  II.  tig.  17  (not  PI.  V,  figs.  4-7  =  S.  herrk-l-i). 
Si/riiu/othi/ris  carfcri  Scliuchert,  ISiJO:  Nintji  Ann.  Rept.  New  York  State  Geologist, 

p.  30.     Keyes,  1895:    Geol.  Surv.  Missouri,  \'ol.  V,  Pt.  II,  p.  87,  PI.  XL,  fig.  10. 
i'^iniiii/oilu/ris  haunihalensis  Hall  aiid  Clarke,  189.5:  Pal.  New  York,  Vol.  VIII,  Pt.  II, 
PI.  XXV,  tigs.  33-35. 

I  have  adopted  for  this  species  the  synonymy  composed  by  Schuehert,^ 
who  has  given  tlie  specific  limitations  of  these  forms  more  detailed  study 
than  any  other  investigator.  The  material  from  the  Yellowstone  National 
Park  includes  only  four  specimens,  one  of  which  is  the  external  cast  of  a 
dorsal  valve,  shown  on  PI.  LXXI,  fig.  la;  the  others  are  three  ventral 
valves,  exfoliated  so  as  to  be  almost  internal  casts.  These  specimens  agree 
well  with  Hall's  description  and  with  Meek's"  figures  of  Spirifer  cuspidaias  (f) 
which  are  here  reproduced  for  reference.  The  dorsal  cast  shows  the  peculiar 
"textile"  surface  ornamentation  of  the  genus,  and  the  shell  substance,  where 
preserved,  gives  evidence  of  being  punctate.  Therefore,  although  the  char- 
acteristic structures  of  foramen  and  beak  have  not  been  observed,  reference 
to  the  genus  and  to  the  species  under  the  genus  seems  to  be  justified 

It  should  be  noticed  that  one  of  the  ventral  valves  above  referred  to 
has  every  character  of  the  specimen  figured  by  White  as  Sijringothijris 
extenuatus  (Wheeler's  Rept.  U.  S.  Geogr.  Surv.  W.  lOOth  Merid.,  Vol.  IV, 
1877,  p.  88,  PI.  V,  figs.  <da-'dd). 

Formation  and  locality:  Madison  limestone,  divide  between  Gallatin 
River  and  Panther  Creek,  Gallatin  Range;  W.  H.  Weed.  Crowfoot  Ridge, 
Gallatin  Range,  top  of  bed  25 ;  J.  P.  Iddings  and  G.  M.  Wright.  Limestone 
bluff"  south  side  of  Soda  Butte  Creek,  northwest  of  Abiathar  Peak,  Absaroka 
Range;  J.  P.  Iddings.  Waverly  and  Burlington  age.  Licking  County,  and 
Bedford,  Cuyahoga  County,  Ohio;  Burlington,  Iowa;  Marion  and  Pike 
coimties,  Missouri;  White  Pine  and  Eureka  districts,  Nevada;  near  Clen- 
deniiin,  Montana. 


'  Niutb.  Ann.  Rept.  New  York  State  Geologist,  p.  30. 

=  U.  S.  Geol.  Expl.  40tb  Par.,  Vol.  IV,  PI.  Ill,  ligs.  11,  lla. 


560  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

EUiAIETRIA  Hall,  1864. 

EUMETRIA    VERNEIULIANA    Hall. 
PL  LXVIII,  figs.  12«,  V2b. 

Retzia  verneuilana  Hall,  1858:   Geol.  Surv.   Iowa,  Vol.  I,  Pt.  II,  p.  657,  PI.  XXIII, 

figs.  \a-\(l.     Hall,  1S5.S:  T'raus.  Albany  lust.,  Vol.  IV,  p.  9. 
Retzia  vera  Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  704,  PI.  XXVII,  figs.  3rt-3e. 

Hall,  18G3:  Sixteeutb  Kept.  New  York  State  Cab.  Nat.  Hist.,  p.  55,  figs.  1-3, 

p.  59. 
Retzia  vernenili  Hall,  18()3:  Ibid.,  p.  55,  fig.  2. 
Eumetria  verneuilana  Whit&nVl,  1882:  Bull.  Am.  Mus.  Nat.  Hist.,  Vol.  I,  p.  50,  PL 

VI,  figs.  28-30. 
Eumetria  verneuiliana  Hall,  1883:  Twelfth  Rept.  State  Geologist,  Indiana,  p.  335,  PL 

XXIX,  figs.  28-30. 
Retzia  radialix  Walcott,  1884:  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  220,  PL  VII,  figs. 

5,  5rt  (5^?). 
Eumetria  verneuiliaHa  and  vera  Hall  aud  Clarke,  1893:  Pal.  New  York,  Vol.  VIII,  Pt. 

II,  p.  117,  figs.  104,  105;  PL  LI,  figs.  13-20,34-37;  PL  LXXXIII,  figs.  26,  27. 

In  the  Mississippi  Valley  Eumetria  verneuiliana  is  couiined  to  tlie  St. 
Louis  and  Chester  divisions  of  the  Lower  Carboniferous  series.  It  includes 
a  number  of  shells  varying  extremely  in  size,  proportion,  and  surface  sculp- 
ture, but  which  it  has  not  yet  been  possible  to  subdivide  and  establish  as 
independent  specific  types. 

The  same  type  of  shell,  however,  appears  much  earlier  in  the  Lower 
Carboniferous;  for  in  the  Kinderhook  division  we  find  Eumetria  aUirostris 
White, ^  Hiistedia  triangularis  Miller,-  Acamhona  osagensis  Swallow,^  Retzia  f 
circularis  MiWer,*  Retzia?  plicata  Miller,"  and  Retzia  pojycana  Swallow,^  all 
externally  similar  and  more  or  less  closely  related  forms. 

The  geiuis  Acambona  includes  mostly  species  from  Lower  Carbonifer- 
ous horizons,  but  the  internal  structure  of  tlie  genus  is  imperfectly  known, 
and  externally  it  is  inseparable  from  Eumetria,  even  Eumetria  verneuiliana. 

E.  verneuiliana,  as  it  occurs  in  the  Madison  limestone,  does  not  attain 
the  size  often  seen  in  specimens  from  the  Mississippi  Valley.     It  is,  on  tlie 


'  1862.  Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  IX,  p.  2S. 

"1894.  Eighteentli  Aim.  Rept.  Geol.  Surv.  ludiau!!.  p.  31.5,  PI.  IX,  tigs.  25,  26. 

n860.  Ti-ans.  St.  Louis  Acad.  Sci.,  Vol.  I,  p.  053. 

n894.  Eighteeuth  Ann.  Rept.  (ieol.  Surv.  Indiana,  p.  316,  PI.  IX,  figs.  32-34. 

"1894.  Ibidem,  p.  310,  PI.  IX,  figs.  29-31. 

"1860.  Trans.  St.  Louis  Acad.  Sci.,  Vol.  I,  p.  654. 


LOWER  CARBONIFEROUS  FOSSILS.  561 

whole,  small,  finely  plicate,  and  profusely  punctate,  but  showing  considera- 
ble variation  in  size,  shape,  and  ])lication.  The  largest  specimen  is  16  mm. 
long  and  of  the  same  width ;  but  it  is  badly  crushed.  Another  example, 
more  nearly  the  average  size,  is  11.5  mm.  long  and  the  same  in  width;  it 
has  about  twenty -eight  strige.  A  third  specimen  is  14  mm.  long,  5.5  mm. 
wide,  and  is  ornamented  with  about  thirty-eight  striae.  These  data  show 
the  range  of  variation  among  the  specimens  in  the  collection. 

I  have  not  been  able  to  verify  the  generic  reference  of  this  form  by 
the  study  of  internal  structure,  but  on  external  evidence  it  can  not  be 
distinguished  from  the  species  to  which  I  have  referred  it. 

It  is  probable  that  Terehratula  marcyi  Shumard  belongs  to  this  same 
specific  type,  and  if  so,  as  it  has  priority  of  date  over  Eumetria  verneuiliana 
by  four  years,  the  name  will  have  to  be  changed  to  E.  marcyi. 

Formation  and  locality:  Madison  limestone,  Limestone  bluff  north  of 
Little  Sunlight  Creek,  Absaroka  Range;  Arnold  Hague.  East  side  of 
Gallatin  River,  west  of  Electric  Peak;  amphitheater  east  of  Bannock  Peak, 
Gallatin  Range,  bed  28;  W.  H.  Weed.  Crowfoot  Ridge,  Gallatin  Range, 
top  of  bed  25;  J.  P.  Iddings  and  G.  M.  Wright.  Same,  top  of  bed  26,  top 
of  bed  27,  bed  28;  J.  P.  Iddings  and  W.  H.  Weed.  Slide  east  side  of 
Gallatin  River,  below  Fan  Creek.  St.  Louis  and  Chester  horizons,  Wash- 
ington and  Crawford  counties,  Arkansas;  Floyd  County  and  elsewhere  in 
Indiana;  Alton,  Illinois;  Green  County,  Missouri;  Iowa;  Cumberland 
Mountain,  Tennessee. 

ATHYRIS  McCoy,  1844. 

Athyris   lamellosa  Ldveilld. 

PI.  LXXI,  fig.  7a. 

Spirifer  lamellosus  L6veill(5,  1835:  Mem.  Soc.  Geol.  de  France,  1st  series, Vol.  II,  p.  39, 

figs.  21-23. 
Athyris  lamellosa  Meeli,  1875:  Pal.  Ohio, Vol.  II,  p.  283,  PI.  XIV,  fig.  Ga,  6b.    Hall  and 

Clarke,   1893:   Pal.  New  York,  Vol.  VIII,  Pt.  II,  p.  90,  PI.  XLVI,  figs.  16-20. 

Herrick,  1888:  Bull.  Denison  Univ.,  Vol.  Ill,  p.  49,  PI,  II,  fig.  7. 

This  species  has  been  identified  in  the  Yellowstone  National  Park  from 
one  locality  only,  where,  however,  it  can  scarcely  be  considered  rare.  As 
there  exhibited,  it  more  nearly  resembles  the  form  figured  by  Hemck  from  the 
lower  "  Wavei'ly"  of  Ohio  (loc.  cit.,  PI.  II,  fig.  7)  than  that  of  Meek  (loc.  cit. 

MON  XXXII,  PT  II 36 


562  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

PI.  XIV,  fig.  6),  or  Hall  and  Clarke  (loc  cit.,  PI.  XLVI,  figs.  16-20).  This 
will  be  seen  by  comparing  the  figure  given  on  PL  VI,  fig.  la,  which  repre- 
sents a  somewhat  crushed,  exfoliated  specimen,  with  the  illustration  alcove 
cited.  The  rather  unusual  variation  in  shape  among  these  forms,  especially 
in  regard  to  the  length  and  straightness  of  the  hinge  line,  may  in  part  be 
accounted  for  by  the  fact  that  some  of  the  specimens  are  casts,  "the  thick 
shell  of  the  rostral  region  when  present  causing  the  hinge  to  appear  sl^.ortei'." 
(Meek,  loc.  cit,  p.  285.) 

I  suspect  that  none  of  the  forms  will  prove  to  be  quite  identical  with 
A.  JameUosa  of  Leveill(^.  Compared  with  L(iveill(i's  illustrations  the  speci- 
mens from  the  Yellowstone  National  Park  are  less  elongated  transversely, 
and  lack  the  high,  sharp  fold  and  sinus  that  characterize  the  type,  which  has 
in  addition  the  projecting  lip  of  the  anterior  margin  bilobate  through  an 
acute  emargination.  A  still  furthei-  point  of  difference  is  that  in  the 
American  forms  the  beak  is  uniformly  smaller  and  incurved  so  as  to  conceal 
the  foramen,  which  is  well  shown  in  the  type. 

Athyris  ashJandensis  of  Herrick  may  be  a  synonym  of  A.  lameUosa. 

In  the  exfoliated  condition  in  which  the  shell  occurs  it  might  be  referred  a 
priori  to  either  Athyris  (sensu  stricto)  or  Cliothyris.  The  only  related  forms 
with  which  it  is  necessary  to  compare  it  are  Athyris  incrassata  and  Cliothyris 
crassicardinalis  White,  and  CI.  roissyi  Walcott.  It  can  without  difficulty 
be  distinguished  from  CI.  crassicardinalis,  for  it  is  much  larger  and  more 
transverse,  with  a  distinct  though  low  median  fold  and  sinus.  On  the 
other  hand,  it  is  considerably  smaller  than  either  A.  incrassata  or  CI  roissyi 
Walcott.  The  shape  is  transversely  elliptical,  with  a  long  and  nearly 
straight  hinge  line,  while  the  other  forms  are  subquadrate  in  outline,  with  a 
much  curved  hinge  margin. 

Formation  and  locality:  Madison  limestone.  Waverly  to  Keokuk, 
Europe;  Sciotoville,  Ohio;  Licking  County,  Ohio;  Lebanon,  Kentucky; 
Crawfordsville,  Indiana;  New  Mexico. 

Athyris  incrassata  Hall(?) 

Athyris  incrassata  Hall,  1858:  Geol.  Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  600,  PL  XII,  fig.  6. 

Hall  and  Clarke,  1893:  Pal.  New  York,  Vol.  VIII,  Pt.  II,  p.  90,  PI.  XLVI,  fig. 

21;  PI.  LXXXIII,  tig.  39. 

The  shell  for  which  I  have  used  this  name  is. represented  only  by  an 
imperfect  cast  of  the  ventral  valve.     It  must  have  measured  between  50  and 


LOWER  CARBO^UFEROUS  FOSSIL«.  "  503 

75  mm.  across,  with  the  length  about  the  same.  The  surface  appears  to  be 
sinootli  except  for  numerous  fine  growth-hues,  and  tliere  is  also  a  shallow 
median  siiuis. 

The  large  .size  of  this  shell  is  the  onh"  trliaracteristic  which  is  practica- 
ble for  identification,  and  I  know  of  only  two  species  of  Athyroids  to  which 
it  could  possibly  be  referred,  CUothyris  ohmaxima  and  Athyrls  incrassata. 
The  spiuose  surface  of  C.  ohmaxima  puts  it  out  of  tlie  question,  wliile  A. 
incrassata  often  ajjpears  quite  smooth.  Still  I  am  not  at  all  clear  that  this 
specimen  is  properl}'  referred  to  A.  incrassata. 

I  am  inclined  to  believe  that  CUothyris  ohmaxima  White  ^  would  more 
properly  be  refeired  to  Athyris  incrassata,  and  that  it  is  perhaps  identical 
with  the  species  under  discussion.  So  far  as  can  be  ascertained  in  the 
fragmentary  and  exfoliated  condition  of  White's  material,  that  form  did  not 
possess  the  spinose  surface,  nor  any  of  the  characters  of  CUothyris. 

Formation  and  locality :  Madison  limestone,  northwest  slope  of  Forellen 
Peak,  Teton  Range;  S.  L.  Penfield.  Burlington  age,  Burlington,  Iowa; 
Quincy,  Illinois;  Hannibal,  Missouri. 

SEMINULA  McCoy,  1844. 

Seminula  madisonensis  n.  sp. 
PI.  LXXI,  figs.  2«,  26,  2c. 

Shell  of  medium  size,  subpentagonal  in  outline,  somewhat  longer  than 
broad.  Surface  marked  by  thick  lamellose  growth-lines,  whose  edges  are 
smooth,  and  not  prolonged  into  sheeted  or  spinose  frills  as  in  Athyris  (sensu 
stricto)  or  Cliothyris.  Sometimes  marked  by  fine  radiating  stria;,  which  are 
not  the  result  of  exfoliation  of  the  fibrous  shell  structure,  but  may  never- 
theless be  structural.     Convexity  moderate. 

Ventral  valve  rather  flat,  with  a  shallow  angular  sinus  which  can  be 
traced  indistinctly  nearly  to  the  beak.  Beak  rather  large  and  not  strongly 
incurved.  Dorsal  valve  broadly  angular  in  cross  section;  fold  defined  for 
a  short  distance  by  shallow  converging  sulci.  The  rostral  angle  of  the 
ventral  valve  is  nearly  90°;  that  of  the  dorsal  valve  is  obtuse. 

Length  of  the  type  specimen,  19  mm.;  width,  16.5  mm.;  thickness, 
11.5  mm. 


'Wheeler's  Kept.  U.  S.  Geogr.  Surv.  W.  100th  Merid.,  Vol.  IV,  1877,  p.  94,  PI.  V,  fig.  12. 


564  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

This  shell  occurs  in  the  upper  beds  of  the  Madison  limestone,  and  as 
it  bears  at  first  sight  a  strong  resemblance  to  the  general  type  of  S.  suhtilita 
Hall,  I  referred  it  to  that  form.  A  comparison  with  specimens  of  S.  suhtilita 
from  the  type  locality,  near  Weston  on  the  Missouri  River,  reveals  certain 
differences  which  seem  to  prove  the  two  forms  distinct. 

8.  suhtilita^  is  somewhat  larger  than  S.  madisonensis,  nan-ower  in  pro- 
portion to  its  length,  with  the  widest  portion  near  the  anterior  margin,  so 
that  the  outline  is  subtriangular.  S.  madisonensis,  on  the  other  hand,  is 
widest  near  the  middle  of  the  shell,  and  the  outline  is  pentagonal. 

The  sinus  in  S.  subtiUta  is  broad  and  shallow,  not  apparent  more  than 
one-third  the  shell  length  back  of  the  anterior  margin.  The  anterior  sinu- 
osity is  nearly  rectilinear,  with  subparallel  sides.  The  dorsal  valve,  on  the 
contrary,  can  scarcely  be  said  to  have  any  con-esponding  fold,  as  that 
structure  falls  into  the  general  curvature  of  the  valve,  which  is  highly 
arched.  In  8.  madisonensis  the  sinus  is  no  deeper  than  in  8.  suhtilita,  but  it 
is  angular  and  can  be  traced  back  to  the  umbonal  region.  The  sinuosity 
is  triangular  and  the  fold  is  defined  for  a  short  distance  by  lateral  sulci. 

In  shells  of  the  same  size  8.  suhtilita  is  more  obese  than  the  other,  the 
dorsal  valve  especially  being  highly  tumid,  particularly  about  the  beak, 
which  is  narrow,  high,  and  pinched.  The  ventral  beak  also  is  more  deeply 
incurved  than  is  the  case  in  8.  madisonensis,  and  the  rostral  angle  is  more 
acute. 

Formation  and  locality:  Madison  limestone,  head  of  Conant  Creek, 
Teton  Range;  W.  H.  Weed. 

Seminula  madisonensis,  var.  pusilla,  n.  var. 

PI.  Lxxi,  figs.  3«,  m. 

In  bed  28,  Crowfoot  Ridge,  Gallatin  Range,  and  also  probably  600 
feet  above  the  stream  at  the  limestone  bluff  north  of  Little  Sunlight  Creek, 
Absaroka  Range,  occurs  scantily  a  small  Seminula  which  I  provisionally 
refer  to  8.  madisonensis  as  a  variety  of  the  same.  It  is  specifically  distinct 
from  other  members  of  the  genus  observed,  and  is  perhaps  distinct  from 
8.  madisonensis  also. 

I  have  seen  only  four  or  five  specimens  of  this  type,  but  these  indicate 
that  it  is  much  smaller  than  8.  madisonensis,  and  more  elongate;  the  ventral 

'  See  PI.  LXXI,  figs,  ia-id. 


LOVVEK  CARBONIFEROUS  FOSSILS.  565 

valve  more  highly  arched  both  lougitudiiuilly  and  transversely;  sinus  not 
so  distinct. 

Length,  11  mm.;  width,  !)  mm. 

Formation  and  locality :  Madison  limestone,  limestone  bluff  north  of 
Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream;  Arnold 
Hague. 

Seminula  humilis  n.  sp. 

PI.  LXXI,  figs.  0«,  (>h,  6c. 

Shell  moderately  gibbous,  small,  circular.  Surface  smooth,  except 
for  a  few  growth-lines. 

Ventral  valve  nearly  circular,  but  for  the  beak,  which  is  rather  large 
and  strongly  incurved  over  the  other  valve,  completely  concealing  the 
foramen,  which  appears  only  where  broken  back  through  the  rostral  shell. 

Dorsal  valve  circular  in  outline,  moderately  curved;  beak  somewhat 
prominent  by  reason  of  a  slight  flattening  on  either  side.  The  dorsal  valve 
has  an  indistinct  fold  and  the  ventral  valve  an  insignificant  sinus,  which  are 
perceptible  only  by  a  sinuosity  in  their  anterior  margins. 

Length  of  a  medium-sized  specimen,  15  mm.;  breadth,  14.5  mm.;  thick- 
ness, 9  mm.  Length  of  a  somewhat  smaller  individual,  12.5  mm.;  breadth, 
11.5  mm.;  thickness,  7.5  mm. 

Were  it  not  that  S.  tmsatchensis  is  an  Upper  Carboniferous  form, 
while  this  one  is  found  in  the  lower  beds  of  the  Lower  Carboniferous,  I 
would  have  unhesitatingly  referred  it  to  White's  species.  The  great  anterior 
thickening  of  the  shell,  which  appears  to  individualize  the  latter  type,  is 
due  to  old  age,  and  can  not  be  considered  a  specific  character.  Otherwise, 
if  occurring  in  the  same  beds,  the  two  forms  could  scarcely  be  distinguished. 

Seminula  humilis  also  approaches  Spirigera  formosa  and  Sj).  euzona,  both 
of  Swallow.  These  forms,  however,  are  marked  by  a  high  fold  and  corre- 
sponding deep  sinus,  while  Sp.  formosa  is  said  to  have  a  punctate  shell, 
and  radiating  striae  when  exfoliated  (fibrous  shell  structure?).  These 
characters  are  decisive  in  separating  Swallow's  species  from  the  one  in 
question. 

Formation  and  locality:  Madison -limestone,  Hunter  Peak,  Absaroka 
Range;  T.  A.  Jaggar.  Crowfoot  Ridge,  Gallatin  Range,  lower  and  upper 
part  of  bed  27,  bed  28,  bed  31 ;  J.  P.  Iddings  and  W.  H.  Weed.  Stinking- 
water  Valley,   below  mouth    of    the    canyon,   Absaroka    Range;    Arnold. 


566  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Hague.  West  of  Antler  Peak,  Gallatin  Range;  A.  C.  Gill.  Summit  of 
peak  west  of  same;  cherty  belt,  Bighorn  Pass,  Gallatin  Range;  Crowfoot 
Ridge,  Gallatin  Range,  top  of  bed  24;  J.  P.  Iddings.  Head  of  Conant 
Creek,  Teton  Range;  W.  H.  Weed. 

SeMINULA -IMMATURA    n.  Sp. 
PI.  LXXI,  figs.  5a,  5b,  5c,  5<1. 

Shell  rather  small,  ovate,  gibbous.  Length  somewhat  exceeding  the 
widtli.  Dorsal  valve  full,  highest  at  the  umbo,  without  a  fold,  but  slightly 
emarginated  in  front;  beak  small,  inflated,  deeply  incm-ved.  Ventral  valve 
oval,  beak  small,  incurved  so  as  to  conceal  the  true  foramen.  There  is  a 
shallow  sinus,  which,  however,  is  perceptible  only  near  the  anterior  margin, 
forming  there  an  upturned  projecting  lip  to  fill  in  the  emargination  of  the 
opposite  valve,  and  producing  a  sinviousity  in  their  line  of  union. 

Length,  18.5  mm.;  width,  15  mm.;  thickness,  12.5  mm. 

Stratigraphically  this  is  the  lowest  of  the  Seminulas  obtained  in  the 
Yellowstone  National  Park,  of  which  S.  madisonensis  is  the  highest.  The 
obsolete  fold  and  sinus,  the  regular,  deeply  arched  valves,  the  evenly 
rounded,  ovate  shape,  the  tumid  dorsal  umbo  and  incurved  beak,  and  the 
small  resupinate  ventral  beak  are  all  characteristic,  and  sharply  differ- 
entiate it  from  the  latter. 

Compared  with  S.  humilis,  it  is  considerably  larger,  more  tumid;  ventral 
beak  smaller  and  narrower;  beak  of  the  dorsal  valve  larger,  more  inflated 
and  incurved. 

Formation  and  locality:  Madison  limestone,  west  of  Antler  Peak,  Gal- 
latin Range;  A.  C.  Gill. 

CLIOTHYRIS  King,  1850. 

This  genus  (or  subgenus)  is  practically  coextensive  with  the  species 
CI  roissyi  Ldveill^,  as  the  latter  at  present  stands.  Partly  because  the 
character  of  the  surface  ornamentation  renders  it  difficult  to  secure  well- 
pi-eserved  specimens,  the  discrimination  of  species  in  this  group,  if  indeed 
it  has  been  systematically  attempted,  has  not,  I  believe,  proved  successful. 

The  Athyris  roissyi  question  has  thus  become  too  complicated  through 
the  prolonged  sedimentation  of  cliothyroid  forms  to  admit  of  its  ready 
solution.     That  it  is  desirable  to  subdivide  this  group  is  obvious;  that  it  will 


LOWKR  CARBONIFEROUS  FOSSILS.  567 

be  possible  to  effect,  this  scientificall}-  by  the  use  of  constant  characters 
seems  probable.  Just  what  characters  will  assume  such  iini)ort,  a  detailed 
critical  study  of  the  genus  will  develop.  Therefore,  I  have  ventured  to 
recognize  certain  tyiles  in  the  Yellowstone  National  Park  collections  which 
I  feel  confident  to  be  distinct  from  CI.  roissiji  of  Leveill^.  Whether  these 
will  ultimately  prove  tenable  or  be  synonymic  with  other  names  from 
different  horizons,  future  investigations  will  disclose. 

Cliothyris  crassicardinalis  White. 

PI.  LXXI,  fig.  8«. 
Athyris  crassicardinalis  White,  1860:  Jour.  Boston  Soc.  Nat.  Hist.,  Vol.  VII,  p.  229. 

This  species  is  referred  to  the  genus  Cliothyris  on  the  streng-th  of  a 
clause  in  the  original  desciiption,  Avhicli  states  that  "occasional  specimens 
show  fringes  of  considerable  length"  proceeding  from  the  squamose  growth- 
lines.  This,  in  conjunction  with  the  shape,  which  is  not  markedly  wider 
than  it  is  long,  seems  to  make  this  reference  secure.  On  the  other  hand,  not 
having  had  access  to  specimens  from  the  type  locality,  and  as  the  species 
has  never  been  figured,  I  can  consider  my  identification  as  only  provisional. 

In  the  Yellowstone  National  Park  tbe  type  here  called  CI.  crassicardi- 
nalis ranges  from  the  bottom  to  the  top  of  the  Madison  limestone.  It  is 
seen  to  be  a  rather  small,  nearly  circular  shell,  slightly  wider  than  long, 
lenticular.  Fold  and  sinus  indicated  only  by  a  slight  emargination  of  the 
anterior  outline.  Beaks  small  and  pointed,  that  of  the  ventral  valve  being 
usually  incurved  so  as  to  conceal  the  foramen.  The  surface  is  covered  with 
numerous  imbricating  lamellose  expansions,  which  under  good  preservation 
are  seen  to  be  subdivided  into  long  spines.  The  large  specimen  figured  on 
PI.  LXXI,  fig.  8a,  measures  15  mm.  in  width  by  14  mm.  in  length,  but 
the  average  size  seems  to  be  somewhat  less  than  this. 

This  form  is  perhaps  identical  with  the  one  figured  in  Mon.  U.  S.  Geol. 
Surv.,  Vol.  VIII,  PI.  XVIII,  fig.  5,  under  the  name  of  Athijris  hirsuta. 

It  is  often  extremely  difficult  in  practice  to  separate  CI.  crassicardinalis 
from  other  forms  found  in  the  same  beds — that  is,  when  one  or  both  are 
ill  preserved  in  one  way  or  another.  Exfoliated  specimens  might  easily  be 
referred  to  the  allied  genera  Athyris  or  Seminula.  On  the  other  hand, 
where  single  valves  occur  embedded  in  limestone,  from  which  they  break 
exfoliated  and  with  the  convex  side  upward,  concealing  the  area,  it  is  very 


568  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

difficult  to  distinguish  even  ventral  valves  from  the  genera  Reticularia  and 
Martinia.  It  is  only  by  a  careful  system  of  comparison  of  the  poor  with 
more  perfect  specimens  that  the  proper  affinities  can  be  ascertained. 

The  greatest  difficulty  is  experienced  in  the  case  of  Semmida  Immilis, 
especially  when  the  material  is  scanty  and  poorly  preserved. 

Unfortunately,  this  is  the  usual  condition.  The  characteristic  surface 
ornamentation  renders  the  genus  Cliothyris  peculiarly  liable  to  exfoliation. 
Usually  the  spines  have  been  broken  away,  their  base  giving  the  lamellae  a 
scalloped  appearance.  When  the  shell  is  entirely  gone,  casts  of  the  interior 
show  only  a  few  heavy  growth-lines.  When  exfoliation  has  obliterated  sur- 
face characters,  reliance  must  be  placed  upon  other  peculiarities  in  distin- 
guishing CI.  crassicardinalis  from  Semhiula  Immilis.  The  shell  of  the  former 
is  less  convex  and  the  beaks  are  more  attenuate.  These  characters  do  not 
always  afford  satisfactory  results;  yet  I  am  unable  to  designate  others. 
The  two  species  occur  together  at  several  localities,  notably  from  the  upper 
part  of  bed  27,  Crowfoot  Ridge,  Gallatin  Range,  but  it  so  happens  that 
they  are  there  especially  well  preserved  and  then-  distinctive  characters 
shown  in  the  clearest  manner. 

Where  the  area  is  concealed,  exfoliated  specimens  might  well  be  taken 
for  the  young  of  Martinia  rostrata  or  the  reverse,  but  the  latter  will  be  seen 
to  have  a  more  prominent  beak,  and  to  be  provided  on  the  ventral  valve 
with  a  shallow  but  perceptible  sinus  reaching  to  the  extremity  of  the  beak. 
Reticularia  cooperensis  is  more  transverse  and  the  ventral  valve  more 
elevated. 

Formation  and  locality:  Madison  limestone,  limestone  bluff  north  of 
Little  Sunlight  Creek,  Absaroka  Range,  600  feet  above  the  stream;  Arnold 
Hague.  Upper  Gallatin  Valley;  divide  between  Gallatin  River  and  Panther 
Creek,  Gallatin  Range;  east  face  of  Antler  Peak,  Gallatin  Range;  W  H. 
Weed.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25;  J.  P.  Iddings  and 
G.  M.  Wright.  Same,  upper  part  of  bed  27,  bed  28,  bed  29,  bed  31 ;  J.  P. 
Iddings  and  W.  H.  Weed.  Summit  of  peak  west  of  Antler  Peak,  Gallatin 
Range ;  south  slope  of  same ;  summit  of  Three  River  Peak,  Gallatin  Range ; 
south  base  of  Quadrant  Mountain,  Gallatin  range;  cherty  belt.  Bighorn 
Pass,  Gallatin  Range;  J.  P.  Iddings.  Crowfoot  Ridge,  Gallatin  Range,  bed 
24;  A.C.Gill.  Northof  Owl  Creek,  northeast  slope  of  Teton  Range;  W.  H. 
Weed.     Kinderhook  age,  Burlington,  Iowa. 


LOWER  OAltBONIFEKUUS  FOSSILS.  569 

Cliothyris  crassicaedinalis,  var.  nana.  ii.  var. 

Pi;  LXXI,  (ig.  9rt. 

The  fonn  here  refeired  to  is  a  rare  one,  and  I  am  in  doubt  whether 
to  consider  it  only  young  or  dwarfed  specimens  of  CI.  crassicardinalis,  a 
true  variety  of  the  same,  or  a  distinct  species.  Its  occurrence  is  restricted 
to  two  or  three  locahties,  where  it  is  not  uncommon  to  find  familiar  types 
represented  by  unusually  small  indiAaduals.  It  has  not  been  possible  to 
ascei'taiu  whether  this  shell  is  a  true  Athyris  (sensu  stricto)  or  belongs  to 
the  genus  Cliothyris,  though  the  circularity  of  its  outline  favors  the  latter 
reference. 

The  shell  is  very  small,  nearly  circular  in  shape,  moderately  convex. 
Beaks  small,  surface  ornamented  by  numerous  close,  regular,  imbricating, 
concentric  lamellae.  It  occurs  in  a  limestone  and  is  always  more  or  less 
exfoliated.  There  is  no  fold  or  sinus,  but  both  valves  have  a  mesial  flatten- 
ing, which  in  some  shells  is  quite  marked.  In  size,  shape,  and  general 
appearance  this  form  is  very  close  to  specimens  of  CI.  hirsuta  from  Spergeu 
Hill,  Indiana. 

Length,  about  0.30  inch ;   width,  nearly  the  same. 

Formation  and  locality  :  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  Crowfoot  Ridge,  Grallatin  Range,  top  of  bed  25; 
G.  M.  Wright. 

Cliothyris  roissyi  Walcott  (non  Ldveilld). 

Athyris  royssii  Walcott,  1884:  Mon.  U.  S.  Geol.  Surv.,  Vol.  VIII,  p.  280,  PI.  XVIII, 
flgs.  9,  9ft. 

I  have  referred  to  this  species  a  single  large  Athyroid  which,  though 
so  exfoliated  as  to  appear  almost  smooth,  yet  bears  so  strong  a  resemblance 
to  the  specimen  referred  by  Walcott  to  CI.  roissyi  (loc.  cit.)  that  I  can  not 
but  believe  them  identical.  There  is,  liowever,  one  striking  difference, 
namely,  in  the  size  of  the  ventral  beak,  that  in  my  collection  being  of 
medium  size,  the  other  extremely  minute.  But  as  both  specimens  are  more 
or  less  crushed,  it  seems  that  this  is  only  an  appearance  due  to  relative  dis- 
placement of  the  two  valves. 

The  generic  position  of  the  form  figured  by  Walcott,  which  shows  very 
clearly  the  overlapping   spinose    lamellae    characteristic    of  Cliothyris,   is 


570     GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

beyond  all  question.  Not  so  the  specimens  figured  by  Meek/  and  doubt- 
full)^  referred  by  him  to  Leveille's  species.  In  comparing  this  form  with 
the  one  under  discussion,  I  find  it  different  not  only  from  it  but  also  from 
the  European  type.  The  shell  is  large,  thick,  transversely  elliptical;  fold 
but  slightly  defined,  sinus  broad  and  shallow,  Avith  a  sharp  median  sulcus; 
surface  lamellose  with  thick  layers,  which,  on  the  best-preserved  surfaces, 
•show  no  trace  of  having  been  produced  into  spines.  The  ventral  beak  is 
rather  large,  not  strongly  incurved,  and  instead  of  being  furnished  with  a 
round  pedicle  aperture,  as  shown  in  the  figure,  a  careful  study  of  the  rostral 
portion  discloses  that  this  appearance  is  due  to  a  fracture  which  has  also 
partially  removed  the  shell  covering  the  arch  of  the  beak,  and  that  below  the 
point  where  the  pedicle  opening  is  indicated  in  the  figure  there  is  the  anom- 
alous character  of  an  open  triangular  delthyriuni.  These  facts  are 
developed  from  a  study  of  the  type  material  itself,  which  in  the  figured 
specimen  alone  preserves  the  ventral  beak  entire,  or  nearly  so.  As  the 
form  seems  to  be  distinct  from  anything  yet  described  from  the  same 
horizon,  I  propose  for  it  the  name  Atliyris  mira. 

The  specific  identity  of  CI.  roissyi  Walcott  with  Leveille's  species  I 
hold  to  be  doubtful. 

That  form  as  figured  by  its  author  is  smaller  (34.5  mm.  in  width  by  22.5 
mm.  in  length)  and  more  deeply  folded,  the  two  depressions  defining  the 
fold  being  so  deep  and  triangular  as  to  give  the  shell  a  trilobate  appear- 
ance. The  fold  is  surmounted  by  a  faint  sulcus  ("?),  resulting  in  a  slight 
emargination  of  the  anterior  border.  Beak  not  incurved,  so  that  the  open 
round  foramen  is  a  noticeable  character.  The  surface  is  marked  b}"  not 
very  numerous  but  strong  lamellar  expansions,  whose  ragged  edges  suggest 
that  they  may  have  been  the  origin  of  the  characteristic  spinose  orna- 
mentation of  the  genus  Cliothyris.  In  the  specimens  from  the  Yellowstone 
National  Park  and  the  Eureka  district  the  fold  and  sinus  are  scarcely 
discernible.  The  latter  has  a  small,  sharp  beak,  whose  deep  incurvature 
completely  conceals  the  foramen.  That  from  the  Yellowstone  National 
Park  shows  an  indefinable  aperture,  partly  beneath  the  beak,  partly  broken 
through  it.  This  contradiction  is  doubtless  due  to  the  same  displacement 
which  makes  the  beak  of  one  specimen  seem  so  small,  that  of  the  other 
comparatively  so  large. 

'  1877.     King'8  U.  S.  Geol.  Expl.,  40th  Par.,  Vol.  IV,  PI.  IX,  figs.  3,  3o,  3S. 


LOWER  CARBONIFEROUS  FOSSILS.  571 

ForiiKition  and  locality :  Madison  limestone,  Crowfoot  Ridg'e,  Gallatin 
Range,  bed  "JS;  J.  P.  Iddinjrs  and  W.  H.  Weed.  Same,  top  of  bed  24;  J.  P. 
Iddings.  Keokuk  to  Kaskaskia;  Europe;  Mississippi  Valley;  White  Pine 
and  Eureka  districts,  Nevada;  Salt  Lake  City,  etc.,  Utah;  Lake  Valley 
mining  district,  etc.,  New  Mexico;  Lake  County,  Colorado;  Guatemala; 
Bonijardin  and  Itaituba,  Brazil. 

CONOCARDIUM  Bronn,  1835. 

CoNOCARDiuM  puLCHELLUM  White  and  Whitfield  (?) 

PI.  LXVI,  fig-.  14rt. 

Conocardium  pulchelbim  White  and  Whitfield,  1S62:  Proc.  Boston   Soc.  Nat.  Hist., 
Vol.  VIII,  p.  299. 

In  the  absence  of  identified  material  I  am  not  sure  that  the  reference 
to  White  and  Whitfield's  species  is  correct,  for  I  have  but  a  single  specimen, 
so  that  it  is  impossible  to  determine  the  range  and  normal  expression  of  the 
shell;  while  C.  pulchellum  has  not  been  figured,  at  least  by  its  authors;  and 
a  description  unaccompanied  by  illustrations,  especially  in  this  genus,  is 
almost  sure  to  be  unsatisfactory. 

My  shell  is  small,  not  very  convex.  Truncation  of  the  anterior  margin 
slightly  concave,  nearly  the  same  length  as  the  straight  hinge  line,  which 
it  meets  at  an  obtuse  angle.  Posterior  cardinal  angle  rounded.  Ventral 
margin  sloping  and  curving  from  the  posterior  angle  to  the  anterior  trunca- 
tion. Posterior  wing  somewhat  flattened  and  concentrically  rugose.  Sur- 
face otherwise  marked  by  about  twenty-five  radiating  striae,  which  are 
strong  and  abrupt,  leaving  between  them  spaces  greater  than  their  own 
diameter.  Length  along  the  hinge  line,  6.-5  mm.;  greatest  diameter  (from 
posterior  cadinal  angle  to  the  junction  of  the  ventral  margin  with  the 
anterior  truncation),  12.5  mm. 

This  species  seems  to  have  some  points  of  resemblance  with  C.  napo- 
leonense  Winchell,  but  it  is  nearer  White  and  Whitfield's  form. 

C.  A.  White'  has  proposed  the  name  Conocardium  semiplenum  for  a  form 
from  the  same  region  as  that  under  consideration.  It  belongs  likewise  to 
the  same  type  of  shell,  as  comparisons  are  made  with  C.  trigonale  Hall, 
which  C.  pulchellum  also  resembles.     It  is  not  improbable  that  he  may  have 


■  U.  S.  Geol.  Surv.  W.  100th  Meridian,  Vol.  IV,  1877,  p.  94. 


572     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

had  in  hand  the  same  form  with  which  I  am  deaUng,  but  his  descriptive 
remarks  are  too  general  to  render  the  species  identifiable. 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  bed  24;  A.  C.  Gill.     Kinderhook  age,  BurUngton,  Iowa. 

NATICOPSIS  McCoy,  1844. 
Naticopsis  (?)  sp. 

PI.  LXVI,  fig.  13a. 

There  is  only  one  specimen  of  this  gastropod,  an  internal  cast  in  a 
siliceous  matrix.  The  peritreme  is  incomplete  and  there  is  no  telling  to 
what  extent  the  lower  whorls  are  broken  dwa)'.  Specific  identification  is 
therefore  out  of  the  question.     It  appears  to  belong  to  the  genus  Naticopsis. 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  24;  J.  P.  Iddings. 

LOXONEMA  Philhps,  1841. 

LOXONEMA  (?)  sp. 
PL  LXVI,  fig.  9a. 

This  species  consists  of  the  cast  of  a  rather  large  elongate  gastropod 
shell,  probably  belonging  to  the  genus  Loxonema.  The  specimen  consists 
of  four  whorls  and  part  of  a  fifth,  and  is  very  gradually  tapering.  It  some- 
what resembles  L.  tenuiUneaium  Swallow,  of  the  Chouteau  limestone,  but 
the  sides  converge  less  rapidly  and  the  peripheral  outline  of  each  whorl  is 
much  flattened.  The  shell  must  have  been  very  thin,  for  the  convolutions 
are  now  almost  in  contact. 

Length  of  the  imperfect  specimen,  27  mm.;  width  at  the  base,  12.5  mm.; 
width  at  the  top,  7.5  mm. 

Formation  and  locality:  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  26;  J.  P.  Iddings  and  W.  H.  Weed. 


LOWER  OAKBONIFEROUS  FOSSILS.  573 

STRAPAROLLUS  Montfort,  1810. 

Straparollus  utahensis  Hall  and  Whitfield. 

PI.  LXVI,  figs.  lOa,  10b,  10c. 

Uvomphalus  [Straparollus)  utahensis  Hall  and  Wliitlield,  1877:  King's  U.  S.  Geol. 
Expl.  40tli  Par.,  Vol.  IV,  p.  Ii59,  PI.  IV,  flg.s.  20-L'3, 

This  genus  is  represented  in  the  collection  from  eight  or  ten  localities, 
but  the  specimens  are  in  so  poor  condition,  being  worn  or  broken,  that  a 
specific  identification  was  a  matter  of  difficulty.  The  beds  from  which 
the  material  was  derived  are  mostly  the  lower  strata  of  the  Madison  lime- 
stone, but  some  specimens,  indistinguishable  from  the  others  in  their  present 
imperfect  condition,  occur  near  the  very  top  of  the  same  formation. 

It  was  evident  at  first  sight  that  the  Yellowstone  National  Park  form 
was  close  to  Etiomphalus  luxus  White,  and  Eii.  utahensis  Hall  and  Whitfield. 
After  a  careful  comparison  of  the  thi-ee  types  the  balance  of  the  evidence 
seemed  to  favor  an  identification  with  Eu.  utahensis,  and  a  section  through 
one  of  the  specimens  justified  the  conclusion.  It  will  be  remembered  that 
the  two  species  just  mentioned  are  both  from  the  Rocky  Mountain  region, 
occurring  in  Waverly  rocks,  and  often  found  at  the  same  locality.  Eu.  luxus 
is  somewhat  smaller  than  Eu.  {Straparollus)  utahensis.  The  whorls  are 
flattened  on  top,  with  a  slight  distal  carination.  In  S.  utahensis,  however, 
there  is  a  strong  carination  on  the  summit  of  each  whorl,  from  which  the 
sides  slope  away  nearly  plane,  one  toward  the  center,  the  other  toward 
the  periphery.  This  proved  to  be  the  case  with  the  specimen  sectioned, 
but  it  is  not  at  all  improbable  that  some  of  the  other  smaller  specimens 
may  belong  to  Eu.  luxus. 

The  shell  of  S.  utahensis  is  thin,  but  thickened  on  top  and  on  the  two 
sides  to  form  the  carinations  (PI.  LXVI,  fig.  10c).  The  outer  side  of  each 
whorl  as  well  as  the  top  is  carinated,  and  the  shell  on  the  inner  side  is  also 
considerably  thickened,  but  indented  to  receive  the  carina  of  the  preceding 
whorl.  The  interior  cross  section,  therefore,  is  circular  or  elliplical,  and 
all  distinguishing  characters  are  lost  when  the  shell  is  reduced  to  a  cast. 

This  species  should  be  compared  with  Euomphalns  ohtusus  Hall  (Geol. 
Surv.  Iowa,  Vol.  I,  Pt.  II,  p.  623),  which  was  described  from  the  Oolitic 
limestone  of  Burlington,  Iowa. 


574  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Formation  and  locality :  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  divide  between  Gallatin  River  and  Panther  Creek, 
Gallatin  Range;  summit  of  Antler  Peak,  Gallatin  Rang-e;  amphitheater  east 
of  Bannock  Peak,  Gallatin  Range,  bed  30;  W.  H.  Weed.  Crowfoot  Ridge, 
Gallatin  Range,  top  of  bed  26,  lower  part  of  bed  27,  bed  28,  bed  31;  J.  P. 
Iddings  and  W.  H.  Weed.  Waverly  age.  Dry  Canyon,  Oquirrh  Mountains; 
Ogden  and  Logan  canyons,  Wasatch  Range,  Utah. 

PLAT YC ERAS  Conrad,  1840. 

This  genus  is  represented  by  specimens  which  are  rather  scarce 
numerically  and  as  to  size  much  below  the  average.  Taken  as  a  whole, 
they  are  closely  similar  to  the  group  of  Waverly  Platycerata  figured  by 
Keyes  in  Geol.  Surv.  Missouri,  Vol.  V,  PI.  LIII,  figs  la-Id,  2-8,  9a,  db.  In 
a  genus  Avhere  the  species  var)^  so  enormously  within  themselves — where, 
in  fact,  it  may  almost  be  said  that  there  are  no  species — my  material  is 
much  too  scanty  and  fragmentary  to  show  the  range  of  specific  variation 
and  afford  the  concept  of  a  specific  type.  Accordingly,  no  elaborate  effort 
has  been  made  to  identify  the  material  with  existing  species,  much  less  to 
propose  new  names,  and  it  has  seemed  best  to  describe  each  form  without 
using  specific  appellations. 

Form  A. 

This  form  is  found  on  Crowfoot  Ridge,  Gallatin  Range,  from  the  top 
of  bed  24.  It  is  small  and  loosely  coiled.  The  apex  is  wanting,  but  the 
whole  specimen  appears  to  have  completed  little  more  than  half  a  turn. 
The  apical  portion  is  twisted  slightly  to  the  left  (looking  at  the  anterior 
peripheral  face),  and  the  base  expands  rapidly,  but  unsymmetrically,  flaring 
a  little  more  on  the  side  toward  which  the  apex  is  turned — the  left.  There 
is  a  broad  carination  on  the  front  face,  delimited  by  the  two  shallow 
grooves.  Aperture  subcircular.  This  form  appears  to  be  close  to  P. 
cornuforme,^  W^inchell,  but  that  shell  is  said  to  be  planorboid,  while  in  this 
the  apex  is  distinctly  turned  to  the  left.  It  also  resembles  P.  vomerium '  of 
the  same  author  in  size  and  in  the  nature  of  the  carination.  Both  these 
species  are  of  Waverly  age. 

'Winchell,  1863:  Proc.  Acad.  Nat.  Sci.  Philadelphia,  pp.  18,    19;  and  Keyes,  loc.  cit.,  PI.  LIII, 
figs.  3a,  3i>. 


LOWER  CARBONIFEKOUS  FOSSILS.  575 

Formation  and  locality:  Madison  limestone,  Crowfoot  Ridge,  Gallatin 
Range,  top  of  bed  24;  J.  P.  Iddings. 

Form  B. 

Shell  very  small,  not  spirally  turned;  of  a  conical  or  pyramidal  shape, 
much  inclined.  The  front  is  edged  or  sharply  rounded;  the  back,  under 
the  apex,  is  flat,  meeting  the  right  side,  which  is  more  inflated  than  the  left, 
at  an  angle.  The  angle  at  which  the  posterior  face  meets  the  left  side  is 
ti'uncated.     Peritreme  subquadrate. 

Formation  and  locality:  Madison  limestone,  north  of  Bighorn  Pass, 
Gallatin  Range;  A.  C.  Gill. 

Form  C. 

Larger  than  either  of  the  two  already  described,  yet  not  very  large; 
much  flattened  transversely,  very  rapidly  expanding.  The  right-hand  face 
of  the  fossil  is  somewhat  flat;  more  inflated  on  the  other  side.  Very 
abruptly  rounded  in  front  and  behind.  But  slightly  inclined,  so  that  a  line 
let  fall  from  the  apex  onto  the  posterior  extremity  of  the  peritreme  would 
be  nearly  perpendicular  to  the  plane  of  the  base. 

Formation  and  locality:  Madison  limestone,  north  of  Bighorn  Pass, 
Gallatin  Range;   A.  C.  Gill. 

Form  D. 

PL  LXVI,  figs.  12a,  126,  12c. 

Small,  gradually  expanding  and  closely  inrolledfor  about  one  volution; 
then  very  rapidly  expanding  for  about  half  a  volution,  which  is  highly 
inflated  and  not  in  contact  with  the  involved  portion.  The  latter  is  minute 
and  turned  to  the  left.  The  peritreme  is  broken,  but  appeal's  to  have  been 
subquadrate.  The  sinistral  side  of  the  large  whorl  (that  toward  which  the 
involved  apex  turns)  is  somewhat  flattened;  the  anterior  end  is  sharply 
rounded.  Another  angular  turn,  sinistro-posterior  in  direction,  would  bring 
this  subplanate  face  to  the  original  one  at  an  acute  angle  were  not  their 
junction  truncated  or  broadly  rounded  (f).  Height  about  two-thirds  the 
antero-posterior  diameter.  A  line  fi'om  the  most  posterior  point  of  the 
peritreme  tangent  to  the  involutions  would  be  about  perpendicular  to  the 
plane  of  the  base. 


576  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

This  form,  though  considerably  smaller,  is  closely  similar  to  the  speci- 
men identified  by  Keyes  as  Capulus  paralius  Winchell,  and  figui-ed  on  PI. 
LIII,  fig.  \d,  of  the  work  cited. 

The  largest  of  these  forms  is  about  9  mm.  in  height,  with  a  maxi- 
mum basal  measurement  of  12.5  mm. 

Formation  and  locality :  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak;  south  slope  of  Quadrant  Mountain,  Gallatin  Range; 
A.  C.  Gill 

Form  E. 

PI.  LXVI,  figs,  lla,  116,  lie,  11(1. 

Shell  rather  small,  though  larger  compared  with  the  other  forms  in 
this  collection.  Very  rapidly  expanding.  Laterally  compressed,  being 
flatter  on  the  sinistral  side,  away  from  Avhich  the  small  coil  is  turned. 
Dextral  side  more  inflated;  dorsum  sharp,  almost  carinate.  Shell  marked 
by  concentric  growth-lines,  sinuous,  following  the  shape  of  the  peritreme. 
Peritreme  oval  in  outline. 

This  should  be  compared  with  P.  nehrascense  Meek,^  and  more  espe- 
cially with  Capulus  paralius  Winchell,  as  figured  by  Keyes  (loc.  cit.,  PI. 
LIII,  figs.  \h,  Ic),  Avhich  is  perhaps  not  identical  with  Winchell's  type, 
shown  by  fig.  la  of  the  same  plate. 

Formation  and  locality :  Madison  limestone,  east  side  of  Gallatin  River, 
west  of  Electric  Peak. 

CRUSTACEA. 

PROETUS  Steininger,  1830. 

Proetus  peroccidens  Hall  and  Whitfield. 

PI.  LXXI,  figs.  14a,  146. 

Proetus  peroccidens  Hall  and  Whitfield,  1877 :  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol. 
IV,  p.  262,  PI.  IV,  figs.  28-32. 

This  species  is  represented  in  the  Yellowstone  National  Park  collec- 
tions by  three  cephalic  shields  (without  the  free  cheeks),  which  are  in  exact 
agreement  with  the  descnption  and  figures  of  P.  2)eroccidens.  Each  of  the 
three  heads  was  found  at  a  separate  locality,  but  one  of  them  occurs  on  the 


'  White,  1877:  Wheeler's  U.  S.  Geogr.  Surv.  W.  100th  Merid.,  Vol.  IV,  p.  159,  PI.  XII,  figs.  5o-5d. 


LOWEU  CAKBONIFEKOUS  FOSSILS.  577 

same  block  of  limestone  which  carries  the  pyg-idium  referred  to  P.  loganensis. 
They  are  without  surface  ornamentation.  The  occipital  rinj^'  is  nairow  and 
not  strong-ly  marked.  The  glabella  is  moderately  high,  reaches  nearly  to 
the  anterior  margin,  evenly  rounded  in  front,  about  once  and  a  half  as 
long  as  wide,  sides  parallel  the  greater  distance,  but  expanding  suddenly 
behind.  Marked  by  three  or  four  pairs  of  transverse  furrows.  Of  these 
only  the  posterior  one  is  well  defined,  and  it  is  bent  backward  at  its  inner 
end  so  as  to  be  almost  continuous  with  the  occipital  furrow.  Frontal  border 
narrow,  thick,  elevated.  Greatest  width  of  the  anterior  portion  of  the 
head,  as  limited  by  the  suture  line,  just  equal  to  the  length  of  the  glabella. 
The  suture  lines  contract  gradually,  but  round  out  strongly  for  the  palpe- 
bral lobe,  the  most  convex  portion  of  which  is  not  more  than  oue-fourth  the 
length  of  the  head,  forward  from  the  posterior  edge. 

Formation  and  locality:  Madison  limestone,  east  side  of  Gallatin 
River,  west  of  Electric  Peak;  G.  M.  Wright.  Crowfoot  Ridge,  Gallatin 
Range,  bed  31;  J  P.  Iddings  and  W.  H.  Weed.  East  slope  of  Survey 
Peak,  Teton  Range;  S.  L.  Penfield.  Waverly  age,  Ogden  and  Logan 
canyons,  Wasatch  Range,  and  Dry  Canyon,  Oquirrh  Mountains,  Utah. 

Proetus  loganeksis  Hall  and  Whitfield. 

PI.  LXXI,  fig.  15a. 

Proetus  loganensis  Hall  and  Whitfield,  1877:  King's  U.  S.  Geol.  Expl.  40th  Par.,  Vol 
IV,  p.  264,  PI.  IV,  fig.  33. 

The  identification  of  this  species  rests  upon  a  single  pygidium  which, 
but  for  being  considerably  smaller  in  size,  is  exactly  identical  with  that 
figured  as  the  type  of  P.  loganensis.  The  surface  is  without  ornamentation. 
The  axial  lobe  is  high,  marked  by  eleven  annulations  including  the  termi- 
nal ones.  The  lateral  lobes  have  nine  annulations  each,  which  extend 
down  upon  the  border  and  become  obsolete  upon  the  margin  near  the  edge 
of  the  shell.     It  occurs  associated  with  P.  peroccidens. 

Proetus  peroccidens  and  P.  Joganensis,  both  of  Hall  and  Whitfield,  rest 
upon  three  structural  units — a  small  unornamented  pygidium,  a  laro-e 
pygidium  with  more  annulations,  ornamented  with  pustules  or  nodes,  and  a 
head  with  free  cheeks  more  nearly  corresponding  in  size  with  the  larger 
pygidia,  but  destitute  of  the  ornamentation  which  characterizes  them.    The 

MON  XXXII,  PT  II 37 


578     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

heads  and  larger  pygidia  were  referred  by  the  author  to  P.  peroccidens,  and 
the  small  type  of  pygidiuni  was  described  as  P.  lof/aiiensis. 

In  the  Yellowstone  National  Park  collections  no  pygidia  of  the  type 
of  P.  peroccidens  (the  unornamented  form)  have  been  observed,  but  the 
large  heads  have  been  identified  as  P.  peroccidens,  and  the  small  pygidia  as 
P.  loganensis.  As  the  pygidium  and  a  lai'ge  head  occur  associated  at  the 
same  locality,  even  on  the  same  slab  of  limestone,  there  is  some  presump- 
tive evidence  that  they  should  be  referred  to  the  same  s})ecific  type,  espe- 
cially as  there  is  only  one  kind  of  head  and  one  kind  of  pygidium  known 
from  the  Park.  The  fact  that  both  portions  are  without  ornamentation 
supports  this  view.  The  disparity  in  size,  especially  when  viewed  in 
connection  with  a  similar  condition  of  affairs  in  Utah,  is  opposed  to  it. 

One  of  three  hj-potheses  seems  probable.  Both  species  (and  the 
pygidia  show  that  they  are  two)  may  have  had  unornamented  cephalic 
shields,  similar  in  detail  and  size;  or,  since  it  is  now  known  that  the  two 
species  occur  in  the  same  beds.  Hall  and  Whitfield  may  have  been  in  error 
in  referring  the  cephalon  from  Dry  Canyon  to  the  associated  pygidia;  or, 
the  smooth,  plain  heads  do  not  belong  to  the  smooth  pygidia  with  which 
they  are  associated  in  the  Yellowstone  National  Park,  but  (what  is  not 
intrinsicallv  improbable)  to  the  ornamented  nodose  ])ygidia  with  whicb 
they  occur  at  Dry  Canyon,  as  Hall  and  Whitfield  have  suggested.  More 
evidence  will  be  necessary  before  the  point  involved  in  this  uncertainty 
can  be  ascertained. 

Formation  and  locality:  Madison  limestone.  Crowfoot  Ridge,  Gallatin 
Range,  bed  31;  J.  P.  Iddings  and  W.  H.  Weed.  Waverly  age,  Logan 
Canyon,  Wasatch  Range,  Utah. 


PLATE  LXVI. 


579 


PLATE    LXVI. 

Page, 
Fig.    1.  Atrypa  reticularis 502 

a.  Type  usually  found  in  Yellowstone  National  Park ;  after  Walcott. 
h.  Lateral  view  of  same ;  after  Walcott. 

Devonian,  Eureka  district,  Nevada. 
c.  View  of  another  specimen ;  after  Meek. 

(f)  Middle  Devonian,  Piuon  station,  White  Pine  district,  Nevada. 
Fig.    2.  Atrypa  missoiiriensis 502 

a.  Rostral  view  of  a  small  individual,  of  a  type  common  in  Yellowstone  National 

Park ;  after  Walcott. 

b.  Ventral  aspect  of  same ;  after  Walcott. 

Devonian,  Lone  Mountain,  Nevada. 

c.  Dorsal  view  of  another  specimen  ;  after  Meek. 

Middle  Devonian,  Pinon  station.  White  Pine  district,  Nevada. 

Fig.    3.  Spirifer  engelmanni 504 

a.  An  anterior  view  ;  after  Meek. 

6.  Cardin.al  view,  showing  area  and  foramen ;  after  Meek. 

c.  Side  view  of  same;  after  Meek. 

d.  Dorsal  view  of  same ;  after  Meek. 

Middle  Devonian,  Nevada. 

Fig.    4.  Athyris  rittata  var.  triplicala  n.  var 504 

a.  Lateral  view  of  type  specimen. 
h.  Dorsal  view  of  same, 
c.  Anterior  view  of  same. 

Three  Forks  limestone,  south  side  of  Soda  Butte  Creek,  northwest  of  Abiathar 
Peak,  Absaroka  Range. 
Fig.    5.  Pleurotomaria  isaacsi  (.') .' 505 

a.  Specimen  doubtfully  ideutilied  with  Hall  and  Whitfield's  species. 

b.  Side  view  of  same. 

Three  Forks  limestone,  Wall  Canyon,  Clark  Fork  Valley. 

Fig.    6.  Loxonema  delicalum  u.  sp 506 

a.  View  of  type  specimen,  enlarged. 

Three  Forks  limestone,  south  side  of  Soda  Butte  Creek,  northeast  of  Abiathar 
Peak,  Absaroka  Range. 
Fig.    7.  Platystoma  minutum  n.  sp 506 

a.  Apical  view  of  type  specimen,  enlarged. 

b.  Lateral  aspect  of  same,  enlarged. 

Three  Forks  limestone,  south  side  of  Soda  Butte  Creek,  northeast  of  Abiathar 
Peak,  Absaroka  Range. 

Fig.    8.  Favosites  sp 501 

a.  Silicifled  example,  showing  size  of  corallites  and  character  of  tabulation. 
Three  Forks  limestone,  north  side  of  Soda  Butte  Creek,  Absaroka  Range. 

Fig.    9.  Loxonema  (?)  sp 572 

a.  Lateral  view  of  an  internal  oast. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  26. 
580 


U.  S.  GEOLOGICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.   LXVI 


la 


Ic 


2a 


i'b 


2c 


^ 


3a 


3b 


-J 

lb 


5a 


3c 


3d 


4a   4b      4c 


lOc 


14a 


I  Ic 


I  la 


I  lb 


|-*'T-'»T-!^,. 


'^i 


^ 


lOa 


I  3a 


ii»^  L 


12b 


12c 


DEVONIAN    AND    LOWER    CARBONIFEROUS 
THREE    FORKS   AND    MADISON    LIMESTONES 


THE  HELIOTYPE  PRINTING  CO..  BOSTON 


DESCRIPTION  OF  PLATE  LX VI— Continued.  581 

Fig.  10.  Strapavoltus  iitahcnsiH 573 

a.  Apical  view  of  a  small  specimen ;  after  Hall  and  WhittieM. 

b.  Apical  view  of  a  larfjer,  somewhat  exfoliated  speiimeu;  after  Hall  and  Whitfield. 

Waverly  age,  Dry  C'aiivou.  Utah. 

c.  Section  through  a  specimen  from  Yellowstone  National  Park. 

Madison  limestone,  east  side  of  (Jallatiu  Kiver,  wost  of  Electric  Peak. 
Fia.  11.  Platj/ceras,  form  K 576 

a.  Lateral  view  of  a  small  example  attached  to  an  exfoliated  hase  of  riafjicriiiun 

si/mmelriius. 

b.  Posterior  view  of  same. 

c.  Same  seen  from  above. 

d.  Side  view  of  a  larger  specimen. 

Madison  limestone,  divide  between  Gallatin  River  and  Panther  Creek,  Gallatin 
Range. 

Fig.  12.  Platyceras,  form  i) 575 

a.  View  of  specimen  resting  on  its  base,  as  seen  from  above,  enlarged. 

6.  Side  view  of  same. 

c.  Posterior  view  of  same. 

Madison  limestone,  south  base  of  Quadrant  Mountain,  Gallatin  Range. 

Fig.  13.  A^aticopsis  (f)  sp 572 

a.  Internal  cast  of  a  specimen  from  the  lower  part  of  the  Madison  limestone. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  24. 

Fig.  14.  Conocardium  piilchelliivi  (?) , 571 

a.  View  of  the  only  specimen  found,  enlarged. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bed  21. 


PLATE  LXVII 


583 


PLATE  LXVII. 

Page. 

Fig.  1.  Menophylliivi  (?)  excavatnm  ii.  sp "H 

a.  View  of  a  typical  example  of  this  species. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  lower  part  of  bed  27. 
h.  Longitudinal  section  of  another  specimen,  showing,  hut  not  completely,  the  depth 
of  the  calyce. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bed  31. 

c.  Transverse  section  of  another  specimen  taken  through  the  calyce,  showing  septa 

of  two  orders  slightly  developed. 
Madi.son  limestone.  Crowfoot  Ridge,  Gallatin  Range,  lower  part  of  bed  27. 

d.  Transverse  section  of  the  same  specimen,  taken  a  little  lower  down.     Indications 

of  the  fossula  and  the  commencement  of  the  fossular  wall  can  be  seen.  Septa 
of  the  second  order  are  not  shown  in  the  drawing,  but  appear  in  the  original 
section  as  small  projecting  points. 

e.  Anotlier  section   of  the  same,   still   more  proximal.    The   large  fossula  is   well 

developed;  the  fossular  wall  and  aborted  fossular  septum  are  well  shown. 
Septa  of  the  second  order  are  represented  by  low  ridges,  two  of  which,  not 
shown  in  the  figure,  are  found  on  either.side  of  tlie  fossular  septum. 
/.  Transverse  section  through  another  specimen  referred  to  this  species.  The  fossular 
septum  here  is  extended  clear  through  the  fossula  to  the  opposite  wall,  bisect- 
ing it,  and  the  whole  is  much  thickened  by  stereoplasma. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bed  31. 

Fig.  2.  CUsiophtjllum  teres  n.sp 51* 

a.  Transverse  section  showing  fossula,  columella,  and  tabula  (?).     The  latter  is  not 
adequately  represented  in  point  of  continuance  and  distinctness.     Secondary 
septa,  not  shown  in  the  figure,  can  be  seen  in  the  original,     x  2. 
h.  Another  section  a   little  more  proximal  than  the  above,  and  showing  much  the 

same  characters,     x  2. 
c.  Another  section  still  more  proximal,  from  the  same  specimen.     The  figure  shows  a 

somewhat  too  great  development  of  dissepimental  tissue,     x  2. 
<f.  Another  section  of  same,  still  more  proximal,     x  2. 

Madison  limestone,  summit  of  Three  River  Peak,  Gallatin  Range. 
Fig.  3.  ilicheliniif  placenta 510 

a.  Lower  or  epithecal  surface  of  a  specimen. 

Madison  limestone,  divide  between  Gallatin  Valley  and  Panther  Creek,  near  Big- 
horn Pass,  Gallatin  Range,  bed  24. 

b.  Another  specimen,  showing  size  and  other  characters  of  the  cell  apertures. 

Madison  limestone,  east  side  of  Gallatin  Eiver,  west  of  Electric  Peak. 

Fig.  4.  Syringopora  siircularia  n.sp 510 

o.  Portion  of  a  section  sliowing  size  and  arrangement  of  the  corallites. 
ft.  An  enlargement  of  the  same. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  bed  28. 
Fig.  5.    Syringopora  aculeata  n.sp 509 

a.  Portion  of  a  section  of  the  type  specimen,  showing  size  and  arrangement  of  the 

corallites. 

b.  An  enlargement  of  the  same. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bed  29. 

Fig.  6.  Aiilopora  geometrica  u.  sp 508 

a.  Portion  of  the  corallum  of  type  specimen,  showing  size  and  arrangement  of  the 
corallites. 
Madison  limestone,  cherty  belt,  Bighorn  Pass,  Gallatin  Range. 
584 


U.  8.  OEOLOOICAL   SURVEY 


MONOGRAPH    XXXII     PART    II     PL.   LXVII 


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THE  MELIOTVPE  PRtNTING  CO.,  BOSTON 


PLATE  LXVIII. 


585 


PLATE     LXVIII. 

Paga 

Fig.    1.  Crania  hvvis ^^^ 

a.  Figure  showing  general  character  of  the  specimen  referred  to  this  species. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  24. 
Fig.    2.  Orthothetes  inftatus. 

a.  Figure,  after  Hall  and  Whitfield,  showing  character  of  an  unusually  large  speci- 
men. 
Waverly  age,  Dry  Canyon,  Utah. 

FlG.    3.   Orthothetes  inaqualis ^2- 

a.  Figure,  after  Hall  and  Whitfield,  showing  the  character  of  this  species. 
Waverly  age,  Ogden  Canyon,  Utah. 

riO'7 

Fig.    4.  Chonetes  ornatus ""-' 

a.  View  of  an  average  specimen  showing  outline  and  surface  ornamentation,  slightly 

enlarged. 
6.  Enlargement  of  the  surface. 

Madison  limestone,  east  side  of  Gallatin  River,  west  of  Electric  Peak. 

c.  Another,  more  auriculate  specimen,  similarly  enlarged. 

Madison  limestone. 

d.  Another,  very  obese  specimen,  natural  size. 

Madison  limestone,-  east  side  of  Gallatin  River,  west  of  Electric  Peak. 

Fig.    5.  Chonetes  loganensis "-•' 

a.  View  of  type  specimen  showing  slight  median  sinus;  cardinal  angles  somewhat 
restored;  after  Hall  and  Whitfield. 
Waverly  age,  Logan  Canyon,  Utah. 
6.  A  characteristic  specimen,  from  Yellowstone  National  Park,  with  rounded  cardinal 
angles  and  without  a  sinus. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 
c.  A  dorsal  valve,  twice  enlarged,  showing  shape  and  character  of  the  very  finely 
striate  surface. 
Madison  limestone,  east  side  of  Gallatin  River,  west  of  Electric  Peak. 

Fig.    6.  Product  us  parvi/orviis  n.  sp 536 

a.  Lateral  view  of  a  typical  example. 
b  (lower  figure).  Posterior  view  of  same, 
c.  Outline  of  same,  ventral  aspect. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 
b  (upper  figure).  A  dorsal  valve  referred  to  the  same  species. 
Madison  limestone,  south  of  Forellen  Peak,  Teton  Range. 
Fig.    7.  Producfua  gallatinensh  n.s-p.     (Seealsofig.il) 533 

a.  Anterior  view  of  a  characteristic  specimen. 

b.  Posterior  view  of  same. 

c.  Side  view  of  same. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 

586 


U.  S.  OEOLOQICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.  LXVIII 


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THE  HEUIOTYPE  PRtNTlNG  CO..  BOSTON 


DESOKIPTION  OF  I'LATE  LXVIII— CONTINUED.  587 

I'agft 

Fig.    8.  Productella  cooperensis 528 

(I.  Lateral  view  of  a  specimen  ideutilied  as  Productella  cooperenstH. 

b.  Anterior  view  of  8:ime. 

c.  A  dorsal  valve  associateil  with  the  above  and  referred  to  the  same  species. 

Madison  liniestoiie,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  24. 

Fig.    9.  Productella  cooperensis 528 

a.  A  dorsal  valve  of  a  type  common  in  Yellowstone  National  Park. 
6.  Ventral  valve  of  the  samr  species. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 

Fig.  10.  Productella  uli/era  u.  sp 530 

<(.  A  dorsal  valve  of  a  common  size  and  shape. 

6.  Outline  view  of  a  highly  vaulted  ventral  valve. 

c.  A  very  auriculate  ventral  valve. 

Madison  limestone,  limestone  bluft"  south  side  of  Soda  Butte  Creek,  northwest 
of  Abiathar  Peak,  Abearoka  Range. 

Fig.  11.  Prodticius  yallatinenaia  n.  sp.     (See  also  fig.  7) 533 

a.  Ventral  view  of  the  type  specimen, 
ft.  Anterior  view  of  same. 

c.  Posterior  view  of  same. 

d.  Side  view  of  same. 

Madison  limestone,  divide  between  Gallatin  River  and  Panther  Creek,  Gallatin 
Range. 

Fig.  12.  Eumetria  verneuiliana 560 

a.  Dorsal  view  of  a  somewhat  crushed  specimen  of  a  type  common  in  Yellowstone 

National  Park,     x  2. 
ft.  Side  view  of  same,     x  2. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 


PLATE   LXIX. 


589 


PLATE     LXIX. 

Page. 
Fig.  1.  Caviarophoria  ringens 537 

a.  Ventral  view  of  a  large  specimen. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  tup  of  bed  25. 

b.  Dorsal  view  of  a  smaller  specimen. 

c.  Side  view  of  same. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bed  28. 
Fig.  2.  CamarotaecHa  keirickana  n.  sp 539 

a.  (by  mistake  left  unnumbered  on  plate)  Ventral  valve,  slightly  enlarged. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 

b.  Dorsal  valve,  similarly  enlarged. 

c.  Anterior  view  of  same. 

Madison  limestone,  divide  between  Gallatin  River  and  Panther  Creek,  Gallatin 
Range. 

Fig.  3.  Camarotmchia  metalUca 540 

a.  Dorsal  view  of  a  specimen  identified  by  Hall  and  Whitfield  as  BhynclioneUa  piistii- 
losa  (?);  after  Hall  and  Whitfield. 
Waverly  age.  Dry  Canyon,  Utah. 
S.  Dorsal  view  of  a  large  specimen  from  Yellowstone  National  Park. 

Madison  limestone,  divide  between  Gallatin  River  and  Panther  Creek,  Gallatin 
Range. 

c.  Anterior  view  of  a  smaller  a  specimen  from  Yellowstone  National  Park. 

d.  Side  view  of  same. 

e.  Dorsal  view  of  same. 

Madison  limestone,  northwest  slope  of  Forellen  Peak,  Teton  Range. 

Fig.  4.  CamarotcecMa  sp 542 

a.  Dorsal  valve,     x  2. 

ft.  Front  view  of  same,     x  2. 

Madison  limestone,  limestone  bluff  south  side  of   loda  Butte  Creek,  northwest  of 
Abiathar  Peak,  Absaroka  Range. 

Fig.  5.  Liorhynchus  hagiiei  n.  sp 543 

a.  Dorsal  view  of  type  specimen, 
ft.  Lateral  view  of  same. 

Madison  limestone.  Crowfoot  Ridge,   Gallatin  Range,  cherty  limestone,  top  of 
bed  24. 

Fig.  6.  Dielasma  ntah 544 

a.  Dorsal  view  of  an  imperfect  example. 
6.  Side  view  of  same. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  bod  28. 
c.  Ventral  view  of  type  specimen :  after  Hall  and  Whitfield. 
Waverly  age,  Cottonwood  divide,  Wasatch  Range,  Utah. 

Fig.  7.  Prodiictiis  scabriculus 531 

a.  Side  view  of  a  ventral  valve  from  the  Madison  limestone, 
ft.  Posterior  view  of  same. 

c.  Outline  of  same,  looked  at  from  above. 

d.  Surface  ornamentation,  enlarged. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  toil  of  bed  25. 
590 


U.  S.   QEOLOOICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PU.    LXIX 


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LOWER    CARBONIFEROUS- MADISON    LIMESTONE 


THE  HELIOTVPE  PHiNTINO  CO.,  BOSTON 


IM':SCRIPTION  OF  PLATE  LXIX— Continued.  591 

Paga 
l''io.  8.  rroditcliis  semireticulalua 535 

a.  Ventral  valve,  posterior  view. 

b.  Lateral  aspect  of  same. 

c.  Outline  as  seen  from  above. 

Madison  liiuestone,  Crowfoot  Ridge,  Gallatin  Range,  lower  part  of  bed  27. 
(I.  Dorsal  valve  of  same  species. 

Madison  limestone,  head  of  Couaut  Creek,  Teton  Range. 

Fig.  9.  Product ns  laricosta 534 

o.  Ventral  valve  of  a  specimen  from  Utah,  restored;  after  Hall  and  Whitfield. 

Waverly  age,  Dry  Canyon,  Utah.  ' 

6.  A  ventral  valve  from  the  Madison  limestone,  flat  and  immature  iu  expression. 

Madison  limestone.  Crowfoot  Ridge,  Gall.atin  Range,  top  of  bed  25. 
c.  Lateral  outline  of  a  ventral  valve  of  the  usual  type. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  lower  part  of  bed  27. 


PLATE  LXX. 


593 
MON  XXXII,  PT  II 38 


PLATE    LXX. 

Page. 
Fig.  1.  Spirifer  sp 552 

((.  View  oi  au  unidentified  dorsal  valve. 

Madison  limestone,  east  slope  of  Survey  Peak,  Teton  Range. 

Fig.  2.  Spirifer  striatus  var.  madisonenais  n.  var 551 

a.  Dorsal  view  of  a  large  specimen. 
6.  Side  view  of  same. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  24. 
0.  Dorsal  view  of  a  somewhat  smaller  specimen. 
d.  Side  view  of  same. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin   Range,  ciierty  limestone,  top  of 
bed  24. 
Fig.  3.  Spirifer  eentrovalns 547 

a.  Ventral  valve  of  a  characteristic  form;  after  White. 

Waverly  age.  Mountain  Spring,  Old  Mormon  road,  Nevada. 

b.  A.  characteristic  dorsal  valve;  after  Hall  and  Whitfield. 

Waverly  age.  Dry  Canyon,  Utah. 

c.  Another  type,  probably  no  more  than  varietally  distinct  from  Spirifer  centronaiut, 

described  by  Hall  and  Whitfield  -as  Spirifa-  albapineiisis ;  after  Hall  and  Whitfield. 
Waverly  age,  Logan  Canyon,  Utah. 

d.  A  young  specimen  of  the  general  type  of  Spirifer  albapinensis,  referable  to  Spiri- 

fer centronatus;  after  Hall  and  Whitfield. 
Waverly  age,  Dry  Canyon,  Utah. 

Fig.  4.  Spirifer  centronatus  var.  semifurcatus  n.  var 549 

a.  A  dorsal  valve  of  this  type  in  which  the  incipient  bifurcation  of  the  two  plications 
surmounting  the  fold  is  less  apparent  than  usu.al. 
Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  26. 
Fig.  5.  Martinia  rontrata  n.  sp 553 

a.  Ventral  view  of  a  rather  young  specimen. 

b.  Outline  of  the  same,  viewed  from  one  side. 

Madison  limestone,  east  side  of  Gallatin  Rive'-,  west  of  Electric  Peak. 
0.  Ventral  view  of  au  old  specimen. 

d.  Lateral  outline  of  same,  showing  the  elevated  iiud  produced  beak. 

Madison  limestone. 

e.  A  large  dorsal  valve,  referred  to  this  species. 
/.  Front  view  of  same  in  outline. 

M.idison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 
g.  A  very  young  ventral  valve,  described  by  Hall  and  Whitfield  as  Athyris  planosui- 
cata  (f ).     After  Hall  and  Whitfield. 
Waverly  age,  Logan  Canyon,  Utah. 
Fig.  6.  Seticularia  coopcrensis  var 556 

a.  An  exfoliated  but  otherwise  perfect  ventral  valve.     The  heavy  concentric  lines  are 

due  to  growth.     Between  these  lie  finer  striie,  the  bases  of  the  characteristic 
spinulose  fimbriations, 

b.  Lateral  outline  of  same. 

c.  Posterior  view  of  same. 

Eureka  district,  Nevada,  Lower  Carboniferous. 
594 


U.  S.  GEOLOGICAL   SURVEY 


MONOGRAPH    XXXn     PART    II     PL.   LXX 


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THE  HEUIOTVPE  PRINTING  CO..  BOSTON 


DESCKIPTION  OF  PLATE  LXX— Continued.  595 

Paga 
FlQ.  7.  /{etioularia  (f)  subrotundala 557 

a.  View  of  a  veutral  valve. 

b.  Side  view  of  same. 

Madison  limestone,  near  Monarch,  Montana. 

Fig.  8.  lieticularia  (?)  peculiaria 557 

a.  Ventral  valve,  identified  by  White  with  Shuinard's  species;  after  White. 
6.  Side  view  of  same;  alter  White. 

Waverly  age,  Mountain  Spring,  Old  Mormon  road,  Nevada. 
Fig.  9.  Eeticularia  cooperensis 555 

a.  A  dorsal  valve,  identified  as  R.  cooperensis, 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  26. 

b.  A  ventrnl  valve  from  another  locality. 

c.  Side  outline  of  same. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  upper  part  of  bed  27. 


PLATE   LXXI. 


597 


PLATE     LXXI. 

Page. 
Fig.   1.  Sijringothyrii  carteri 558 

a.  Dorsal  valve  of  a  specimen  from   yellowstone  National  Park,   drawn   from   au 

impression  of  a  natural  mold. 
Madison  limestone,  limestone  bluff  soutb  side  of  Soda  Butte  Creek,  nortliTvest 
of  Abiatliar  Peak,  Absaroka  Range. 

b.  Anterior  view  oif  an  entire  example  of  the  same  species ;  after  Meek ;  figured  by 

that  author  as  Spirifer  (Syringothxjris)  cuspidatus. 

c.  Cardinal  view  of  same,  showing  high  area  and  foramen,  and,  within  the  latter,  the 

transverse  septum  and  internal  tube;  likewise  after  Meek. 
Lower  Carboniferous  (  ?),  White  Pine  district,  Nevada. 

Fig.   2.  Seminula  tnadisonensis n.  sp 563 

a.  Dorsal  view  of  type  specimen. 
h.  Side  view  of  same. 

c.  Interior  of  a  ventral  valve,  showing  hinge  teeth,  pedicle  cavity,  and  posterior  and 
anterior  adductors. 
Madison  limestone,  head  of  Conaut  Creek,  Teton  Range. 

Fig.   3.  Seminula  madisonensis  va,T.pu8SiUa  u.  var 564 

a.  A''entral  valve  of  type  specimen,  showing  shape,  enlarged, 
ft.  Lateral  view  of  same. 

Madison  limestone.  Crowfoot  Ridge,  Gallatin  Range,  bed  28. 

Fig.   4.  Seminula  subtilita 564 

fl.  Dorsal  view  of  a  characteristic  specimen  from  the  type  locality,  for  comparison 

with  Seminula  madisonensis. 
h.  Side  view  of  same, 
c.  Anterior  view  of  same. 

Upper  Carboniferous,  near  Weston,  on  the  Missouri  River. 

Fig.    5.  Seminula  immatura  n.  sp 566 

a.  Dorsal  view  of  a  specimen  with  the  ventral  beak  broken, 
ft.  Side  view  of  same. 

c.  Dorsal  view  of  another  specimen  which  is  somewhat  crushed. 

d.  Side  view  of  same. 

Madison  limestone,  west  of  Antler  Peak,  Gallatin  Range. 

Fig.    6.  Seminula  humilis  n.  Bip 565 

a.  Dorsal  view  of  a  rather  large  specimen. 

6.  Side  view  of  same. 

c.  Dorsal  view  of  a  smaller  specimen  from  the  same  locality. 

Madison  limestone,  Crowfoot  Ridge,  Gallatin  Range,  upper  part  of  bed  27. 

Fig.    7.  Athyris  lamellosa 561 

a.  Ventral  view  of  a  badly  exfoliated  specimen. 

Madison  limestone,  Yellowstone  National  Park. 

Fig.    8.  Cliothyris  crassicardinalis 567 

a.  Dorsal  view  of  a  specimen  showing  the  usual  characters  of  size  and  shape,  but 
almost  completely  exfoliated. 
Madison  limestone,  north  of  Owl  Creek,  northeast  slope  of  Teton  Range. 
598 


U.  S.  GEOLOGICAL    SURVEY 


MONOGRAPH    XXXII     PART    II     PL.    LXXI 


3a  .lb 


y/ 


X 


7a 


Sa 


5b 


8a 


w,^ 


Ic 


9a 


13a 


6c 


I  4a 


14b 

8 


I  5a 


13b 


13c 


2c 


2b  2a 


^         ^§; 


6a  6b 


vm 


10^ 


12a 


LOWER    CARBONIFEROUS- MADISON    LIMESTONE 


THE  MELIOTYPE  PRINTING  CO..  BOSTON 


DESCRIPTION  OF  PLATE  LXXI— Continued.  599 


Fig.    9.  Cliothyris  craxeUaidinalis  var.  nana  n.  var 569 

a.  Ventral  view  of  a  somewhat  exfoliated  specimen,  which  is  regarded  as  varietally 
distinct  from  the  above. 
Madison  liraestoue,  Crowfoot  Ridge,  Gallatin  Range,  top  of  bed  25. 

FlO.  10.  Spiri/eriiia  solidirostria 545 

a.  Ventral  valve  ch.iracteristio  of  this  species. 

Madison  limestone,  amphitheater  east  of  Bannock  Peak,  Gallatin  Range,  bed  28. 

Kid.  11.  HolaatercUa  wrvjhti  var.  ame.ricana  n.  var 508 

a.  View  of  an  isolated  spicule  raagnitied  about  twenty  diameters. 

Madison  limestone,  divide  between  Gallatin  Valley  and  Panther  Creek,  near  Big- 
horn Pass,  Gallatin  Range,  bed  24. 

Fn;.  12.  Endothyra  baileyi 507 

a.  An  example  from  Spergen  Hill,  Indiana,  of  a  not  unusual  size,     x  12. 
6.  Another,  smaller  specimen  from  the  same  locality,     x  12. 
Warsaw  group,  .Spergen  Hill,  Indiana. 

Fig.  13.     Endothi/ra  baileyi  var.  jyarva  n.  var 507 

(I,  b.  Two  specimens  of  the  ordinary  character,  from  the  Madison  limestone,     x  12. 
c.       A  small  specimeu  from  the  Madison  limestone,     x  12. 

Madison  limestone.  White  Mouutain,  Absaroka  Range. 

Fig.  14.  Proetiis  peroccidens 576 

a,  b.  Glabella  and  free  cheek  of  the  kind  occurring  in  the  Madison  limestone;  after 
Hall  and  Whitfield. 
Waverly  age,  Dry  Canyon,  Utah. 

Fig.  15.  Proeiua  loyamnsis 577 

a.  Pygidium  of  a  type  associated  with  the  above  in  the  Madison  limestone;  after 
H.all  and  Whitfield. 
Waverly  age,  Logan  Canyon. 


CHAPTER   XIII 


MESOZOIC    FOSSILS. 


By  T.  W.  Stanton. 


The  Mesozoic  fossils  obtained  iu  and  near  the  Yellowstone  National 
Park  and  submitted  to  me  for  study  include  78  species  of  invertebrates,  of 
which  31  are  Cretaceous,  46  are  Jurassic,  and  1  is  from  beds  of  supposed 
Triassic  age.  The  number  of  species  from  a  single  horizon  is  not  large 
enough  to  be  dignified  with  the  designation  "fauna,"  excepting,  perhaps, 
in  one  or  two  cases;  yet  the  study  of  these  fossils  and  the  comparisons 
made  with  known  horizons  have  led  to  some  general  results  that  are  worthy 
of  brief  discussion.  The  subject  will  be  treated  by  geological  horizons, 
and  after  reviewing  the  general  considerations  an  annotated  list  of  the 
species  with  descriptions  of  new  forms  will  be  given. 

TRIASSIC. 

The  Teton  formation,  of  supposed  Triassic  age,  yielded  a  few  speci- 
mens of  a  Lingula  at  a  locality  on  the  summit  of  Quadrant  Peak.  This 
fossil  resembles  Lingula  hrevirostris  M.  and  H.,  from  the  Jurassic  of  the 
Black  Hills,  but  in  the  absence  of  other  fossils  it  should  be  given  little 
weight  in  determining  the  age  of  the  beds.  Linguloid  shells  are  so  slightly 
differentiated  that  it  would  not  be  safe  to  distinguish,  by  them  alone,  even 
between  Paleozoic  and  Mesozoic.  The  determination  of  the  age  of  this 
formation  must,  for  the  present  at  least,  rest  on  the  evidence  of  stratigraphy 
and  lithology.  The  paleontologist  can  only  say  that  the  underlying  beds 
yield  Carboniferous  fossils,  while  the  overlying  formation  has  a  well- 
developed  Jurassic  fauna. 

600 


MESOZOIC  FOSSILS.  601 

The  only  marine  Triassic  fossils  that  have  been  found  in  the  Rocky 
Mountain  region  are  from  the  Lower  Trias,  Ijeneath  the  "Red  Beds"  in 
southeastern  Idaho^  The  very  few  fossils  that  have  been  obtained  from 
the  Red  Beds  farther  south  (in  New  Mexico  and  southern  Colorado)  seem 
to  be  of  fresh-water  origin. 

In  California  and  Nevada,  however,  marine  Triassic  beds  are  well  devel- 
oped, and  have  yielded  a  varied  fauna  which  is  as  yet  mostly  undescribed. 

JURASSIC. 

The  Jurassic  fossils  form  much  the  largest  and  most  important  part  of 
the  Mesozoic  collection.  The  fauna  is  not  large,  but  most  of  the  species 
are  abundantly  represented,  and  in  number  of  species  it  compares  favorably 
with  the  Jurassic  of  other  parts  of  the  Rocky  Mountain  region.  The  col- 
lections are  from  many  localities  in  two  general  areas — one,  which  yielded 
the  most  fossils,  in  the  northwest  corner  of  the  Park,  on  the  headwaters  of 
Gardiner  and  Gallatin  rivers  and  near  the  Yellowstone ;  the  other  on  the 
slopes  of  Sheridan  Peak  and  farther  southwest  of  Snake  River. 

The  fossils  from  all  these  localities  evidently  belong  to  a  single  fauna, 
though  two  zones  are  recognizable,  distinguished  more  by  lithological 
differences  than  by  faunal  peculiarities.  The  upper  zone  of  arenaceous 
limestone  has  yielded  an  abundance  of  RhynchoneUa  gnathojjJiora,  B.  myrina, 
Ostrea  strigilecula,  Camptonectes  pertenuistriatus,  C.bellistriatus,  and  a  few  other 
forms.  Most  of  these  also  occur  in  the  underlying  calcareous  clays  and 
marly  limestones  associated  with  many  other  species,  of  which  the  most 
abundant  are  Pleuromya  siibcompressa,  PJioladomya  kingi,  and  Gryphcea  cal- 
ceola  var.  nehrascensis. 

The  same  fauna  is  represented  in  the  beds  just  beyond  the  northern 
limits  of  the  Park,  at  Cinnabar  Mountain,  where  fossils  that  are  included  in 
the  present  report  were  obtained  by  Dr.  A.  C.  Peale  in  1872.  These  were 
identified  and  some  of  the  species  named  by  Prof.  F.  B.  Meek,-  but  it  was 
not  until  1880  that  they  were  illustrated  and  more  fully  described  by 
Dr.  C.  A.  White.^  Still  earlier  Captain  Raynolds  had  brought  back  Gnj- 
phcea  calceola  var.  nehrascensis  and  a  few  other  fossils  of  this  horizon  from 


'  See  White,  Triassic  fossils  of  soutlieasterii    Idaho :  Anu.  Rept.  U.  S.  Geol.  Surv.  Terr,  for   1878, 
pp. 105-118. 

''Ann.  Rept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  pp.  471-474. 
^Idern  for  1878,  pp.  143-153,  Pis.  XXXVIl  and  XXXVIU. 


602  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Wind  River  Valley,  and  they  were  described  by  Meek  and  Hay  den/  who 
had  previously^  announced  the  discovery  of  Jurassic  fossils  from  the  Black 
Hills.  These  Black  Hills  fossils  are  fully  described  and  illustrated  in  the 
Paleontology  of  the  Upper  Missouri.  Subsequent  geological  explorations 
and  surveys  have  shown  that  the  marine  Jurassic  is  widely  distributed  in 
South  Dakota,  Wyoming,  Montana,  Idaho,  and  Utah,  and  have  made  con- 
siderable additions  to  the  fauna  that  have  been  described  by  White,^  Hall 
and  Whitfield/  Meek"  and  Whitfield.®  All  of  these  authors  seem  to  have 
assumed  that  the  fossils  they  described  belonged  to  a  single  fauna.  At 
least  they  made  no  attempt  to  recognize  distinct  horizons  in  the  Jurassic. 
The  meagerness  of  the  fauna — usually  only  a  few  species  having  been 
obtained  at  any  one  locality — was  perhaps  sufficient  reason  for  not  making 
attempts  of  this  kind.  Prof  Alpheus  Hyatt's  recent  comprehensive  studies 
of  the  earlier  Mesozoic  faunas  of  the  United  States,  and  especially  of  Cali- 
fornia, where  all  the  greater  divisions  of  the  Jura  are  developed,  have  led 
him  to  express  the  opinion  that  both  tlie  Upper  Jura  (Callovian  or  Oxford- 
ian)  and  the  Middle  Jura  (Oolite)  are  represented  in  the  Rocky  Mountain 
region.'  In  the  former  he  places  the  Jurassic  of  the  Black  Hills,  and  of 
Red  Buttes  and  Aurora,  Wyoming,  with  probably  some  localities  in  Utah. 
Of  the  Middle  Jura  he  says:  "The  Oolite  certainly  seems  to  have  been 
found  by  Dr.  Peale  near  the  lower  canyon  of  the  Yellowstone  in  Montana, 
and  out  of  the  few  fossils  from  Utah  described  by  Dr.  White  some  are 
closely  similar  to  those  of  the  inferior  Oolite  at  Mount  Jura." 

It  has  already  been  stated  that  this  collection  of  Dr.  Peale's  belongs 
to  the  same  horizon  that  is  represented  in  the  Park.  It  contained  the  fol- 
lowing species: 

Ostrea  strigilecula.  Trigoiiia  montanaensis. 

Gryphaja  planocoiivexa.  Astarte  meeki. 

Camptonectes  platessiformis.  Cypricardia  baguei. 

Pinna  kingi.  Pleuromya  subcompressa. 

Gervillia  montanaensis.  PLoladomya  kingi. 

Morliola  subimbricata.  Goniomya  montanaensis. 
Trigonia  americaua. 

'Proc.  Acad.  Nat.  Sei.  Phila.,  1861,  p.  437,  and  Paleontology  of  the  Upper  Missouri,  1865,  pp.  74  and  80. 

=  Proc.  Acad.  Nat.  Sci.  Phila.,  1858,  pp.  46,  49-59. 

3U.  S.  Geog.  and  Geol.  Expl.  West  of  100th  Meridian,  Vol.  IV,  Pt.  1, 1875. 

<U.  S.  Geol.  Expl.  40th  Parallel,  Vol.  IV,  Pt.  II,  1877. 

•"■Idem,  Pt.  1, 1877,  and  Simpson's  Rept.  Expl.  Great  Basin,  Utah,  1876. 

•^Newtou  and  Jenney's  Rept.  Geol.  Black  Hills  of  Dakota,  1880,  pp,  344-382. 

'Bull.  Geol.  Soc.  Am.,  Vol.  Ill,  1892, pp.  409-410. 


MESOZOIC  FOSSILS.  603 

Besides  the  species  named,  tliere  are  fragments  of  two  species  of 
ammonites,  and  several  other  forms  are  rejjresented  by  casts  or  other  imper- 
fect material.  All  of  the  species  named  in  this  list,  excepting  Gonio»ii/a 
montanaensis,  occur  at  various  localities  in  tlie  Park,  as  shown  in  the 
annotated  list  of  species  (pp.  608-631). 

Comparatively  few  Jurassic  fossils  are  known  from  Utah,  and  the>'  are 
probably  all  from  one  horizon.  According  to  the  various  reports  published, 
as  well  as  personal  observation  in  both  the  northern  and  southern  parts  of 
the  Territory,  the  fossiliferous  zone  is  a  calcareous  bed  near  the  base  of  the 
local  Jurassic  sections.  In  Weber  Canyon  it  has  yielded  Cucnlltea  liaguei, 
Pkiiromya  suhcompressa,  Pentacrinus  asteriscus,  and  a  few  other  forms;  in 
Thistle  Canyon  the  pecuhar  Lyosoma  poivelll  was  obtained,  and  in  a  collec- 
tion made  by  Mr.  Robert  Forrester  on  San  Rafael  River  I  have  recoo-nized 
Irigonia  amerkana  and  Pholadomya  Jcingi,  all  of  which  occur  in  the  Park. 
For  these  reasons  I  regard  all  of  the  fossiliferous  Jurassic  beds  now  known 
in  Utah  as  belonging  to  the  same  horizon  that  is  so  well  represented  in  the 
Yellowstone  National  Park. 

The  question  still  remains  whether  the  Jurassic  of  the  Black  Hills 
belongs  to  a  higher  horizon.  There  are  some  facts  in  favor  of  the  opinion 
that  the  Jurassic  fossils  of  the  two  regions  may  not  be  contemporaneous. 
For  example,  a  number  of  the  most  abundant  species  in  the  Yellowstone 
National  Park  region,  such  as  Pleuromya  suhcompressa,  Pholadomija  kingi,  and 
Cypricardia  haguel,  have  not  been  reported  from  the  Black  Hills.  The 
Yellowstone  species  of  Trigonia,  Modiola,  and  Gervillia  are  also  distinct. 
Pseudomonotis  (Eumicrotis)  curta,  which  is  one  of  the  most  abundant  species 
in  the  Black  Hills,  is  represented  in  the  Park  collection  by  a  single  doubtful 
specimen.  No  example  of  Cardioceras  cordiforme  has  been  found  in  the 
Yellowstone  National  Park,  and  several  other  common  Black  Hills  forms 
are  either  absent  or  rare  there. 

On  the  other  hand,  there  is  a  considerable  list  of  species  common  to  the 
two  regions,  among  which  may  be  mentioned: 

Pentacrinus  asteriscus.  Camptonectes  bellistriatus. 

Ehyuchouella  niyrina.  Cami)tonectes  platessiformis. 

Ehyncbonella  gnathophora.  Avicula  wyomingensis. 

Ostrea  strigilecula.  Belemnites  densus. 
Gryphsea  calcepla  var.  nebrascensis.' 


'The  Black  Hills  specimens  of  this  species  are  all  small. 


604  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Many  of  the  species  that  are  considered  distinct  are  closely  related. 
It  should  be  remembered,  also,  that  we  know  only  fragments  of  the  fauna 
that  must  have  existed  at  that  time  if  it  approached  in  size  those  that 
are  now  living.  Whitfield  records  only  43  species  from  all  the  Black  Hills 
country,  and  we  now  have  about  the  same  number  from  the  Yellowstone 
region.  If  more  exhaustive  collections  were  made  in  both  districts,  it  is 
probable  that  the  list  of  common  species  would  be  considerably  increased, 
but  even  as  the  record  stands  it  shows  rather  close  relationship  of  faunas. 
Possibly  the  lowest  Jurassic  beds  in  the  Yellowstone  region  may  be  slightly 
older  than  the  lowest  in  the  Black  Hills,  but  the  difference  in  age  can  not 
be  great — not  great  enough,  as  it  seems  to  me,  to  put  them  in  different  divi- 
sions of  the  Jura.  Throughout  all  the  Rocky  Mountain  region,  wherever 
marine  Jurassic  strata  are  found  they  are  only  a  few  hundred  feet  in  thick- 
ness and  they  rest  directly  on  the  Triassic  "Red  Beds"  or  on  older  forma- 
tions. It  does  not  seem  possible  that  Upper  Jurassic  marine  beds  could 
have  been  deposited  in  the  Black  Hills  and  Wyoming  without  leaving  any 
traces  in  the  Yellowstone,  Montana,  and  Utah — that  is,  the  stratigraphic 
relations  and  the  geographic  distribution  of  the  marine  Jurassic  of  the 
Rocky  Mountain  region  are  in  favor  of  the  idea  that  all  of  these  deposits 
were  made  contemporaneously  in  a  single  sea. 

CRETACEOUS. 

Dakota  (?)  formation. — Thc  collectlou  sliows  that  sevcral  horizons  of  the 
Cretaceous  are  represented  in  the  Park.  The  lowest  of  these,  according 
to  the  geologists,  is  a  thin  bed  of  limestone,  not  far  above  the  local  base  of 
the  Cretaceous  section,  that  is  filled  with  fresh-water  gastropods  and  a  few 
Unios.  This  fauna  at  once  suggests  a  comparison  with  the  fresh-water 
forms  {Lio'placodes  veterniis  and  Viviparus  gUli)  from  beds  of  supposed 
Jurassic  age  overlying  the  marine  Jura  in  Wind  River  Valley,  Wyoming, 
but  these  forms  are  not  represented  in  the  Park  collections. 

The  few  species  obtained  do  not  show  their  generic  characters  very 
distinctly;  still  it  is  evident  that  they  are  not  closely  related  to  the  fresh- 
water Bear  River  fauna  of  southwestern  Wyoming  nor  to  the  few  fresh-water 
forms  known  from  the  Dakota  of  Nebraska,  both  of  which  seem  to  hold 
about  the  same  stratigi-aphic  position  as  this  bed.  There  is  one  other 
possibility,  and  that  is  that  the  Lower  Cretaceous  Kootanie  formation  is 


MESOZOIC  FOSSILS.  605 

represented  here.  It  has  been  recognized  by  means  of  its  fossil  plants  at 
Great  Falls,  Montana,  and  in  the  Black  Hills,  but  its  fresh-water  mollusks 
are  almost  entirely  unknown,  and  the  few  that  have  been  seen  are  entirely 
different  from  these.  All  that  can  now  be  said  concerning  the  age  of  these 
fossils  is  that  they  come  from  a  bed  that  is  conveniently  referred  to  the 
Dakota  on  account  of  its  stratigraphic  position.  I  have  named  three  of 
the  most  common  forms  of  gastropods  from  this  bed,  so  that  they  may  be 
definitely  referred  to,  although  they  are  rather  obscure  and  unsatisfactory 
species. 

Colorado  formation. — The  marine  Cretaceous  beds  on  Snake  River  one-fourth 
to  one-half  mile  above  the  mouth  of  Sickle  Creek  may  be  directly  correlated 
with  the  upper  part  of  the  Colorado  formation  as  it  is  developed  on  the  Mis- 
souri River  near  Fort  Benton.     The  locality  near  Sickle  Creek  has  yielded: 

Inoceramus  uudabundus  M.  and  H.  Inoceramus  flaccidus  White. 

Inoceramus  umbonatus  M.  and  H.  Baculites  asper  Mort.  (?) 

Inoceramus  acuteplicatus  n.  sp.  Scaphites  ventricosus  M.  and  H. 

All  of  these,  except  the  third  and  fourth,  occur  together  in  the  upper 
part  of  the  so-called  Fort  Benton  shales  on  the  Missouri,  and  associated 
with  them  are  Inoceramus  exogyroides  M.  and  H.,  I.  defonnis  Meek,  I.  temii- 
rostris  M.  and  H.,  Veniella  morfoni  M.  and  H.,  and  Phohidomya  papyracea  M. 
and  H.,  and  a  few  undescribed  species. 

This  well-characterized  zone  was  included  in  the  Fort  Benton  shales 
by  Meek  and  Hayden  when  they  gave  that  name  to  the  "No.  2"  of  their 
Cretaceous  section,  and  they  regarded  all  these  dark  shales  near  Fort 
Benton  as  the  equivalent  of  the  shales  underlying  the  Niobrara  limestone 
in  Nebraska,  Kansas,  Colorado,  and  elsewhere.  The  fact  is,  however,  that 
the  Niobrara  also  is  represented  by  shales  in  this  upper  Missouri  region, 
and  the  fossils  indicate  that  this  zone  is  really  the  equivalent  of  the  upper 
portion  of  the  Niobrara.  The  evidence  for  this  statement  rests  on  the 
occurrence  of  several  of  the  above  species  in  the  Niobrara  limestone  and 
overlying  shales  of  Colorado  and  in  the  equivalent  Austin  limestone  of 
Texas,  and  also  on  the  absence  of  all  these  species  except  Veniella  morfoni 
from  beds  lower  than  the  Niobrara  in  the  same  region  and  elsewhere.  In 
Colorado  Inoceramus  deformis  is  the  most  characteristic  species  of  the  Nio- 
brara limestone.  Recently  Mr.  Gr.  K.  Gilbert  has  collected  Inoceramus 
umbonatus  from  shales  in  the  Niobrara  above  the  limestone  near  Pueblo, 


606  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Colorado,  and  it  is  probable  that  the  type  of  I.  flaccidus  canie  from  about  the 
same  horizon.  I.  umbonatus  and  /.  exogyroides  are  reported  from  the  Austin 
limestone  of  Texas,  and  Baculites  asper  (?)  occurs  in  the  same  formation. 
The  European  I.  involutus,  which  is  very  closely  related  to,  if  not  identi- 
cal with,  I.  uiubonatus,  is  also  confined  to  the  Emscher  Mergel,  according  to 
Schliiter,  which  appears  to  be  the  homotaxial  equivalent  of  the  Niobrara. 

The  fact  that  within  the  Colorado  formation  experience  has  shown  the 
various  species  of  luoceramus  to  be  good  guide  fossils  for  the  different 
zones  gives  this  evidence  of  a  few  species  greater  weight  than  it  would 
have  otherwise. 

The  name  Colorado  formation  has  come  into  general  use  for  the 
combined  equivalents  of  the  Fort  Benton  and  Niobrara,  and  it  is  a  very 
convenient  term,  especially  in  the  regions  where  the  lithological  differences 
are  not  clearly  marked. 

A  fragment  referable  to  Scaphites  ventricosus,  obtained  on  the  southeast 
spur  of  Electric  Peak,  makes  it  probable  that  the  shales  there  also  belong 
to  the  iipper  part  of  the  Colorado  formation.  The  same  horizon  is  repre- 
sented at  Cinnabar  Mountain,  just  north  of  the  Park,  though  no  Cretaceous 
fossils  from  that  place  are  included  in  these  collections.  Professor  Meek 
examined  fossils  obtained  there  in  1872  and  listed^  Scaphites  ventricosiis, 
Baculites  asper  (f),  and  undetermined  species  of  Tlu-acia,  Trigonia, 
Inoceramus,  and  Ostrea. 

There  are  two  other  localities  in  the  northern  part  of  the  Pai-k,  on 
Fan  Creek  and  the  north  branch  of  Gardiner  River,  that  have  yielded 
an  abundance  of  Ostrea  anomioides,  a  species  that  occurs  in  the  Colorado 
formation  at  several  localities  in  Montana. 

Montana  formation. — Thc  Fort  Picn'e  aud  Fox  Hills  divisious  of  the  Meek 
and  Hayden  section  are  frequently  combined  under  the  name  Montana 
formation  for  reasons  similar  to  those  that  caused  the  union  of  the  Fort 
Benton  and  Niobrara.  In  the  western  part  of  the  Rocky  Mountain  Cre- 
taceous area  it  is  often  difficult  to  draw  a  sharp  line  between  even  these  two 
broader  divisions.  The  lower  part  of  the  section  is  distinctively  Colorado 
and  the  upper  part  distinctively  Montana,  but  there  is  frequently  a  doubtful 
zone  in  which  the  faunas  are  more  or  less  blended.  This  is  especially  true 
in  northern  Utah,  at  Coalville,  and  in  western  Wyoming,  where  both  the 


'Ann.  Kept.  U.  S.  Geol.  Sutw  Terr,  for  1872,  p.  475. 


Ml<:SOZOIC  FOSSILS.  607 

Colorado  and  Montana  formations  contain  several  heavy  beds  of  sandstone 
with  closely  related  littoral  faunas.^  It  is  evident  that  the  seashore  remained 
in  that  region  throughout  nearly  all  of  Upper  Cretaceous  time,  giving  the 
shallow  waters  and  sandy  bottom  favorable  to  the  continuance  of  the  littoral 
fauna  that  was  early  established  there.  The  Colorado  formation  is  easily 
recognized  in  these  sections  by  the  occurrence  of  a  number  of  widely  dis- 
tributed characteristic  species,  but  for  some  unexplained  reason  very  few 
of  the  species  that  characterize  the  Montana  formation  farther  east  and  north 
occur  there. 

This  phase  of  the  Cretaceous  is  well  developed  on  Hams  Fork,  in 
western  Wyoming,  and  it  extends  northward  from  there  nearly  to  the 
southern  boundary  of  the  Park,  for  it  is  well  represented  in  the  collection 
from  a  sandstone  on  Glade  Creek  and  at  other  localities  near  Snake  River 
in  the  same  region.  Fossils  are  abundant,  but  only  about  20  species 
were  obtained.  Judging  from  the  fauna,  the  horizon  is  not  very  far  from 
that  of  the  Colorado  shales  near  Sickle  Creek — probably  a  little  above 
them — and  it  is  provisionally  referred  to  the  lower  part  of  the  Montana 
formation.  Several  of  the  species  occur  at  Coalville,  Utah,  and  in  south- 
western Wyoming,  and  some  of  them  there  range  down  into  the  Colorado 
formation. 

More  thorough  collecting  from  all  the  Cretaceous  beds  exposed  in  the 
Yellowstone  National  Park,  and  a  little  farther  north  and  east,  will  probably 
give  both  phases  of  the  Upper  Cretaceous  faunas  in  one  section  and  enable 
us  to  assign  these  sandstones  to  a  more  definite  place  in  the  standard  Upper 
Cretaceous  section. 

In  the  following  list  of  species  references  are  usually  given  only  to 
the  first  description  and  to  publications  in  which  the  species  is  figured. 
For  fuller  references  consult  Boyle's  Catalogue  of  American  Mesozoic 
Invertebrates:    Bull.  U.  S.  Geol.  Surv.  No.  102. 


'  See,  for  a  fuller  discnssion  of  this  subject,  The  Colorado  formation  autl  its  iu vertebrate  fauua: 
Bull.  U.  S.  Geol.  Surv.  No.  106,  pp.  37-46. 


608  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

ANNOTATED  LIST  OF  SPECIES,  WITH  DESCRIPTION  OF  NEW 

FORMS. 

TRIASSIC  (?)  SPECIES. 

LINGULA  sp.  undet. 

A  few  specimens  of  Lingula  from  beds  on  the  summit  of  Quadrant 
Peak,  supposed  to  be  of  Triassic  age,  closely  resemble  the  Jurassic  Lingula 
brevirostris  M.  and  H.  from  the  Black  Hills. 

JURASSIC   SPECIES. 
ECHINODERMATA. 

Pentacrinus  asteriscus  Meek  and  Hayden. 

Pentacrinus  asteriscus  Meek  and  Bayden,  1855:  P roc.  Acad.  Nat.  Sci.  Phila.,  p.  49. 
White,  187.5:  Geogr.  aud  Geol.  Surv.  W.  lOOtb  Meridian,  Vol.  IV,  Pt.  I,  p.  162, 
PI.  XIII,  figs.  6a,  b.     Clark,  1893:  Bull.  U.  S.  Geol.  Surv.  No.  97,  p.  26,  PI.  Ill, 

figs.  2a-d. 
Pentacrinites  asteriscus  Meek  and  Hayden,  1865:  Palfeont.  Upper  Missouri,  p.  67,  PI. 

Ill,  figs.  2a,  b,  and  fig.  in  text.    Whitfield,  1880:  Geol.  Black  Hills  Dakota,  p. 

345,  PI.  Ill,  figs.  1,  2. 
Pentacrinus  whitei  Clark,  1893:  Bull.  U.  S.  Geol.  Surv.  No.  97,  PI.  Ill,  figs.  4a^fl. 

This  species,  which  is  known  only  from  portions  of  the  columns,  occurs 
in  collections  from  divide  between  Fawn  Creek  and  Gallatin  Valley,  from 
the  slopes  of  Mount  Sheridan,  and  from  west  of  Snake  River,  north  of  Berry 

Creek. 

The  joints  of  the  columns  vary  in  diameter,  in  thickness,  and  in  the 
depth  of  the  reentrant  angles,  but  they  do  not  vary  more  in  these  respects 
than  do  the  different  portions  of  the  stem  in  a  single  individual  of  a  recent 
Pentacrinus.  The  joints  of  the  upper  part  of  the  column  are  always  thinner, 
more  distinctly  star-shaped,  and  differ  in  all  other  details  from  those  of  the 
lower  portion. 

The  name  P.  wUtei  was  proposed  by  Prof  W.  B.  Clark  for  large,  thin 
joints  with  deep  reentrant  angles,  but  the  author  of  the  species  informs  me 
that  he  has  abandoned  the  name  for  reasons  similar  to  those  just  given,  and 
in  a  forthcoming  monograph  of  the  Mesozoic  Echinodermata,  of  the  United 
States  he  will  refer  all  the  known  American  Jurassic  Pentacrini  to  P. asteriscus. 


MESOZOIC  FOSSILS.  609 


ECHINOIDEA. 


Frag^nientarv  casts  of  one  or  more  species  of  e(;liiuoi(ls  were  obtained 
nt-ar  the  lower  canyon  of  the  YeUowstone  River  and  at  a  hicaHty  north  of 
Berry  Creek,  a  tributary  of  Snake  River.  Tliey  are  doubtless  new  species, 
but  they  are  not  sufficiently  well  preserved  for  generic  determination,  and 
we  must  therefore  wait  for  additional  and  better  material. 

BRACHIOPODA. 

Rhynchonell.v  myrina  Hall  and  Whitfield. 

Rhynchonella  myrina  Hall  and  Whitfield,  1877:  U.  S.  Geol.  Expl.  40tli  Parallel,  Vol. 
IV,  Pt.  II,  p.  284,  PI.  VII,  figs.  1-5.  Whitfield,  1880 :  (ieol.  Black  Hills  Dakota, 
p.  347,  PI.  Ill,  fig.  6,  not  fig.  7. 

The  tj'pe  of  this  species  is  a  finely  plicate  shell  with  aljout  eight  plica- 
tions in  the  median  sinus.  In  Prof  R.  P.  Whitfield's  later  publication  he 
has  united  with  it  the  much  more  coarsely  plicate  forms,  with  only  three  or 
foiu-  plications  in  the  median  sinus,  that  have  usually  been  referred  to  R. 
(jnathophora.  As  the  numerous  specimens  in  the  present  collection  do  not 
show  the  intermediate  varieties  of  form  and  sculpture,  I  prefer  to  treat  them 
as  distinct  species. 

Typical  B.  myrina  occurs  at  a  number  of  localities  in  the  northwest 
corner  of  the  Park  and  near  Snake  River  southwest  of  it,  in  the  hard 
arenaceous  limestone. 

Rhynchonella  gnathophora  Meek. 

PI.  LXXII,  figs.  1-4. 

Bhynchonella  gnathophora  Meek,  1804:  Geol.  Surv.  California,  PaliTBOiit.,  Vol.  I,  p.  39, 

PI.  VIII,  figs.  la-/. 
Rhynchonella  ijnathophora  1  Hall  and  Whitfield,  1877:  U.  S.  Geol.  Expl.  40th  Parallel, 

Vol.  IV,  Pt.  II,  p.  284,  PI.  VII,  fig.  (J. 
Rhynchonella  myrina  (H.  and  W.)  Wliitfield,  1880:  Geol.  Black  Hills  Dakota,  p.  347, 

PI.  Ill,  fig.  7,  not  fig.  6. 
Rhynchonella  sp.  Meek  and  Hayden,  1865:   Pahtont.   Upper  Missouri,  p.  71,  PI.  Ill, 

fig.  4. 

The  specimens  referred  to  this  species  have  nearl}'  the  same  outlines 
as  i?.  myrina,  but  they  are  somewhat  more  capacious  and  mucli  more  coarsely 
plicate.     The  type  of  R.  myrina  has  thirty  ])lications  on  each  valve,  with 

MON  XXXII,  PT  II 39 


610  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

eight  in  the  mediau  sinus,  while  the  phcations  on  these  shells  vary  from 
fourteen  to  twenty,  with  three  or  four  in  the  median  sinus,  three  being 
much  the  more  common  number.     A  few  specimens  have  only  two. 

I  have  not  seen  Meek's  types  from  the  Jurassic  of  California,  but 
specimens  from  the  Mormon  sandstone  near  Taylorsville  (probably  Meek's 
original  locality)  have  been  kindly  loaned  by  Professor  Hyatt  for  com- 
parison. These  are  larger  than  any  of  the  Utah  or  Yellowstone  specimens, 
and  none  of  them  has  less  than  four  plications  in  the  median  sinus,  but  in 
all  other  respects  they  agree  quite  closely.  All  the  figured  specimens  from 
the  Black  Hills  and  Rocky  Mountain  region  above  referred  to  have  been 
examined,  and  I  have  no  doul)t  of  their  specific  identity.  In  Yellowstone 
National  Park,  where  the  species  is  very  abundant  in  the  upper  zone  of  the 
Jurassic  and  occasionally  occurs  in  the  underlying  shales,  the  specimens  are 
usually  small,  many  of  them  being  no  larger  than  the  one  from  the  Black 
Hills  figured  by  Meek  and  Hayden. 

It  is  known  from  northwestern  Colorado  and  from  the  Uinta  Moun- 
tains, Utah,  and  it  occurs  in  the  Park  near  the  northern  and  Lake  heads  of 
Fawn  Creek;  on  south  slope  of  ridge  south  of  Gray  Mountain;  south  side 
of  Fan  Creek  Pass;  on  saddle  at  head  of  Fawn  Creek,  northeast  of  Monu- 
ment Peak,  in  beds  100  feet  above  principal  fossiliferous  horizon  of  Jurassic; 
in  saddle  west  of  south  head  of  Gardiner;  4  miles  north  of  second  crossing 
of  Snake  River,  at  7,500  feet  elevation;  on  hill  northeast  of  Moimt  Everts; 
on  ridge  south  base  of  northwest  slope  of  Flat  Mountain;  at  Mammoth 
Hot  Springs,  on  main  terrace. 

PELECYPODA. 

OSTREA    STRIGILECULA    "White. 

Ostrea  strigilecula  White,  1875 :  U.  S.  Geog.  aud  GeoL  Surv.  W.  100th  Mericliau,  Vol. 

IV,  Pt.  I,  p.  163,  PI.  XIII,  tigs.  3a-d.    1884 :  Fourth  Auu.  Kept.  U.  S.  Geo!. 

Surv.,  p.  281t,  PI.  XXXV,  figs.  0-11.     Whitfield,  1880:  Geol.  Bhick  Hills  Dakota, 

p.  348,  PL  III,  figs.  8-12. 

Specimens  referable  to  this  small  and  somewhat  obscure  species  were 
collected  from  almost  every  locality  with  BJnjnchonelhi  rjimtJi02Jhora  aud  on 
northeast  spur  of  peak  west  of  mouth,  of  Coulter  Creek;  west  end  of  ridge 
southeast  of  Mink  Creek;  Mount  Sheridan;  lower  limestone  on  Fawn 
Creek  plateau;  east  end  of  northeast  spm-  from  Signal  Peak;  saddle  in 
rido-e  west  of  south  head  of  Gardiner. 


MKSOZOIC  FOSSILS.  611 

OsTKEA    ENGELMANNI    Meek. 

Ostrea  enfielmamii  Meek,  18G0:  Proc.  Acad.  Nat.  Sci.  Pliihi.,  p.  .Sll.  1870:  Simpson's 
Kept,  Expl.  (heat  Basin,  Utah,  p.  355,  PI.  Ill,  fig.  «.  Meek  and  Uaydeu,  1865: 
Paliiont.  Upper  Missouri,  p.  73,  flgs.  A,  P>.  Wliite,  1881:  Fourth  Anu.  lle])t. 
U.  S.  (ieoL  Surv.,  p.  289,  PI.  XXXIV,  tigs.  3, 1. 

A  few  frag-ments  and  imnuiture  specimens  of  this  species  were  obtained 
near  the  head  of  drainage  of  northeast  valley  of  Fan  Creek  and  top  of  hill 
3  miles  southeast  of  Gravel  Peak. 

Gbyph.^-:a  planoconvexa  Whitfield. 

PI.  LXXII,  tigs.  II  and  10. 

Grypluvajilanoconvera, 'Whit^eM  1876:  Ludlow's  Kept.  Keconnaissance  from  Carroll, 
Montana,  to  Yellowstone  Park,  p.  142,  PI.  II,  tigs.  9  and  10. 

Shell  of  medium  size,  subcircular  in  outline;  attached  valve  moderately 
convex  with  rather  [)rominent  lieak,  and  in  most  specimens  with  an  obscure 
shallow  furrow  which  separates  a  rather  broad  triangular  lobe  from  the 
body  of  the  shell;  upper  valve  varying  from  nearly  flat  to  deeply  concave; 
surface  marked  onl}'  by  lines  of  growth  and  irregular  concentric  undula- 
tions.    The  cartilage  pit  is  verj'  broad  and  shallow. 

An  average  specimen  measures  57  mm.  in  length,  50  mm.  in  height, 
and  27  mm.  in  thickness  of  the  two  valves  united. 

This  form  was  mentioned  by  MeeP  as  "Gryphsea,  a  small  species  of 
the  form  of  G.  dUatataP  It  also  rese}nbles  some  varieties  of  the  Upper 
Cretaceous  6^.  vesicularis  and  Ostrea  pat'nia.  Whitfield's  type,  from  the 
Bridger  Mountains,  Montana,  is  somewhat  more  convex  than  any  of  our 
specimens,  and  the  figure  does  not  show  any  furrow  or  lobe,  but  I  have  no 
doubt  that  it  is  the  same  variable  species. 

The  specimens  figured  are  from  near  lower  canyon  of  Yellowstone 
River,  collected  by  Dr.  A.  C.  Peale,  and  ridge  southwest  of  second  crossing- 
of  Snake  River,  collected  by  Mr.  W.  H.  Weed.  It  was  also  obtained  on 
north  slope  of  ridge  north  of  Gray  Mountain;  on  divide  at  head  of  Fawn 
Creek;  ridge  west  of  south  branch  of  headwaters  of  Gardiner,  and  near 
Snake  River  3  miles  west  of  mouth  of  Coulter  Creek. 


'  Ann.  Rept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  472. 


612  GEOLOGY  OF  THE  YELL0WST02^'E  NATIONAL  PARK. 

GrypHxEa  calceola  var.  nebrascensis  Meek  and  Hayden. 

PI,  LXXII,  figs.  5-7. 

Gryphcea  calceola  var.  nebrascensis  Meek  and  Hayden,  1861:  Proc.  Acad.  Nat.  Sci. 
Phila.,  p.  •IST.  1805:  PaLtont,  Upper  Missouri,  p.  74,  PI.  Ill,  flgs.  la-e  and  figs. 
A-E  on  p.  75.  Whitfield,  1880:  Geol.  Black  Hills  Dakota,  p.  349,  PI.  Ill,  figs. 
13-10.  White,  1884:  Fourth  Ann.  Ptept.  U.  S.  Geol.  Surv.,  p.  290,  PI.  XXXV, 
figs.  1-5. 

This  is  one  of  the  most  abundant  species  in  the  lower  fossiliferoiis  zone 
of  the  Yellowstone  National  Park  Jurassic,  occurring  in  the  collection  from 
south  slope  of  ridge  south  of  Gray  ]\Iountain ;  south  end  of  northeast  spur  of 
Signal  Peak;  east  side  of  Fan  Creek  Pass;  head  of  north  fork  of  Fawn 
Creek;  saddle  in  ridge  west  of  south  branch  headAvaters  of  Gardiner; 
summit  of  wagon  road  between  Sentinel  Bi;tte  and  Terrace  Mountain,  1 
mile  from  head  of  Swan  Lake  Valley;  hills  west  of  Snake  Eiver,  4  miles 
south  of  second  crossing;  on  north  side  of  old  road  to  Mammoth  Hot 
Springs,  and  slopes  of  Mount  Sheridan. 

The  species  was  originally  described  from  the  Wind  River  Mountains 
and  from  the  Black  Hills,  though  the  specimens  from  the  latter  locality  are 
all  very  small.  Similar  small  specimens,  however,  are  very  abundant  in 
the  Park  collections. 

Lima  cinnabarensis  n.  sp. 

PI.  LXXII,  fig.  8. 

Shell  small,  obliquely  elongate  oval  in  <uitline ;  beaks  large  and  promi- 
nent; hinge  line  short,  the  triangular  ears  being  small  and  inconspicuous; 
anterior  side  straight  or  slightly  concave;  posterior  side  broadly  convex  and 
prominent;  surface  marked  by  lines  of  growth  and  by  about  twenty  promi- 
nent rounded  radiating  ribs,  which  are  not  quite  equal  in  breadth  to  the 
spaces  between  them. 

The  species  is  represented  by  only  tn  o  right  valves,  the  larger  of  which 
is  figured.  It  measixres  16  mm.  in  its  greatest  dimension,  obliquely  down- 
ward and  forward  from  the  beak,  and  10  mm.  across  the  middle  of  the  shell 
at  right  angles  to  that  line;   convexity  about  4  mm. 

No  American  Jurassic  species  has  been  described  with  which  this 
should  be  compared,  except,  perhaps,  the  form  from  Sigutlat  Lake,  British 
Cr)lumbia,  referred  by  Whiteaves  to  Lima  duphcata  Sowerby,  from  which 


MESOZOIC  FOSSILS.  613 

Lima  cinnabarensis  is  distin<i"uislic(l  ])y  its  simple  etjual  ribs.     It  has  more 
resemlilanco  to  the  ('ix'taccous  Lhiui  ntahrnsis  of  the  Coktrado  formation. 

LocaHtv:  Cinnabar  Mountain,  Montana,  where  it  is  associated  with 
Pkitronn/a  siihroiiii>rcssa,  Fholmlomijii  l'ni<j'i,  Trii/onia  montanaensis,  etc. 

Genus  CAMPTUNECrrES  (Agassiz)  Meek. 

Shells  belonging  to  this  genus  are  very  abundant  in  the  Jurassic  of 
the  Rocky  Mountain  region.  In  Yellowstone  National  Park  almost  every 
Jurassic  locality  has  yielded  specimens,  but  in  many  cases  they  are  frag- 
mentary or  mere  casts  that  can  not  be  assigned  to  species  with  any  con- 
fidence. Five  American  Jurassic  species  have  been  described,  of  which 
three  at  least  are  sufficiently  well  characterized  to  be  easily  distinguished 
when  good  specimens  are  examined.  These  are  Caniptonedes  belli striatus 
(to  which  a  new  ^•ariety  is  added  below),  C.  platessiformis,  and  C.  stijgius. 

The  types  of  C.  extenuaUis  are  casts  in  sandstone  that  show  neither 
sculpture  nor  the  forms  of  tlie  ears.  It  may  be  a  distinct  species,  but  it  is 
more  probable  that  it  is  either  the  young  of  C.  bellistriafus  or  the  form  after- 
wards named  C.  perienuistriatns  by  Hall  and  Whitfield.  I  do  not  feel  quite 
certain  that  the  latter  is  distinct  from  C.  bellistriatus,  young  specimens  of 
which  when  slightly  exfoliated  would  be  very  similar;  but  in  the  present 
collection  there  are  many  specimens  that  can  be  most  conveniently  referred 
to  C.  pertenuistriatns,  and  the  name  is  therefore  retained.  All  of  the  species 
mentioned  excepting  C.  sti/r/iiis  are  represented  in  these  collections. 

Camptonectes  bellistriatus  Meek. 
PI,  LXXII,  flg,  12. 

Pecten  hellistriata  Meek,  1860:  Proc.  Acad.  Xat.  Sci.  Pbila.,  p.  311. 

Canqitonectes  betUstriatus  Meek  and  Haydeu,  1805:  Pahvout.  Upper  Missouri,  p.  77, 

figs.  A-D.    Meek,  1876:  Simpson's  Rept.  Expl.  Great  Basin,  Utab,  p.  356,  PI. 

Ill,  figs.  3a-d.    Hall  and  Whitfield,  1877 :  Eept.  U.  S.  Geol.  Expl.  lOtli  Parallel, 

Vol.  IV,  Pt.  II,  p.  289,  PI.  VII,  fig.  13.     Whitfield,   18S0:  Geol.  Black  Hills 

Dakota,  p.  351,  PI.  IV,  figs.  6-11. 
1  Camptonectes  extenuatus  (M.  and  H.)  Hall  and  Whitfield,  1877 :  llept.  U.  S.  Geol. 

Expl.  40th  Parallel,  Vol.  IV,  Pt.  II,  p.  290,  PI.  VII,  flg.  18. 

Imperfect  specimens  that  appear  from  general  form  and  details  of 
sculpture  to  agree  with  this  well-known  species  were  collected  at  head  of 
Fawn  Creek,  upper  bed;  divide  between  Fawn  Creek  and  Gallatin  Valley; 


614  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

south  slope  of  riclg'e  south  ot"  CTi-av  ^louutaiu;  saddle  in  ridge  west  of 
south  branch  of  headwaters  of  Gardiner;  north  side  of  Norris  road  pass; 
hill  southwest  of  second  crossing  of  Snake  River;  west  end  of  ridge  south- 
east of  mouth  of  Mink  Creek,  and  1  mile  from  head  of  Swan  Lake  Valley, 
on  north  side  of  road  to  Manunoth  Hot  Springs. 

As  supplemental  to  the  published  descriptions,  it  may  be  stated  that 
the  left  valve  is  considerably  more  convex  than  the  right  and  that  both 
valves  have  the  same  sculpture.  The  smooth  right  valve  tigured  by  Whit- 
fiekP  is  either  exfoliated  or,  possibly,  another  species.  The  anterior  ear  in 
that  figure  is  different  in  form  from  that  of  C.  belUstriattts,  as  may  be  seen 
on  comparison  with  ouv  figure  of  a  specimen  identified  by  Meek  from  the 
Bighorn  Mountains. 

The  small  specimen  figured  by  Hall  and  Whitfield  as  C.  extenuatus  is 
an  immature  left  valve  of  this  species  or  of  C.  pertenuistriatus. 

Camptonectes  hellistriatus  var.  distans  n.  var. 
PL  LXXII,  fig.  13. 

This  variety,  as  far  as  known,  is  smaller  than  the  typical  form  of  the 
species,  from  which  it  difi^ers  in  having  the  radiating,  impressed,  punctate 
lines  less  closely  arranged  and  consequently  fewer  in  number,  and  it  also 
difters  in  the  outlines  of  the  ears.  The  anterior  ear  is  comparatively  broader, 
with  a  narrower  and  deeper  byssal  notch,  and  the  posterior  ear  is  somewhat 
smaller  and  slightly  less  oblique.     Left  valve  of  this  variety  unknown. 

The  specimen  figured,  which  is  from  near  the  source  of  Gardiner 
River,  has  the  following  dimensions:  Height,  38  nun.;  greatest  length,  38 
mm.;  length  of  hinge  line,  19  mm. 

The  varietv  has  also  been  collected  east  of  Small  Lake,  head  of  Fawn 
Creek,  and  in  north  wall  of  Fawn  Creek. 

Cajiptonectes  pertenuistriatus  Hall  and  Whitfield. 
PL  LXXII,  fig.  11. 

Camptonevtcs  perienuisfriatus  Hall  and  Whitfield,  1877 :  Rept.  U,  S.  GeoL  ExpL  40th 

Parallel,  Vol.  IV,  Pt.  II,  p.  291,  PL  VII,  fig.  17. 
Of.  Camptonectes  extenuatus  Meek  and  Hayden,  18C5:  Palreont.  Upper  Missouri,  p.  78, 

PI.  Ill,  fig.  6. 
The  ijriginal  type  in  the  National   Museum   is  a  young  indiAndual, 


'  Geol.  Black  Hills,  PI.  IV,  tis,'.  10. 


MESOZOIC  FOSSILS.  615 

sliyhtly  flattened  by  pressure  and  somewhat  exfoliated.  Tlie  radiating 
stria"  arc  harelv  visible  luider  a  lens,  and  tliey  are  considerably  exaggerated 
in  the  original  (.-nlargcd  tigure.  It  ditt'ers  from  typical  examples  of  C. 
hcllifitriaius  in  its  more  slender  form  and  smoother  snrface,  the  radiating  strife 
being  almost  obsolete,  though  it  is  sometimes  difficult  to  determine  whether 
this  is  a  natural  feature  or  due  to  exfoliation.  The  doubt  as  to  its  identity 
with  C.  cxteniiatiis  has  already  been  mentioned. 

In  the  Park  it  is  uTost  connnon  in  the  upper  fossiliferous  band  of  the 
Jura,  occurring  on  Gardiner  River  southeast  of  Electric  Peak;  south  slope 
of  ridg-e  south  of  Gray  Mountain;  saddle  west  of  south  head  of  Gardiner; 
west  of  Snake  River,  4  miles  south  of  second  crossino ;  top  of  hill  3  miles 
southeast  of  Gravel  Peak,  northwest  of  Flat  Mountain;  ridge  south  of 
Mammoth  Hot  Springs,  on  main  terrace;  east  slope  of  Mount  Sheridan,  and 
ridge  south  of  Mount  Sheridan. 

Camptonectes  platessiformis  White. 

Caniptonectes  platessiformis  White,  1876:  Greol.  Uinta  Mountains,  p.  93.     1880:  Ann. 

Kept.  U.  S.  Geol.  Surv.  Terr,  for  1S78,  p.  143,  PI.  XXXVII,  fig.  5a. 
Camptonectes  extcnuatm  (M.  and  H.)  Whittield,  1880 :  Geol.  Black  Hills  Dakota,  p.  353, 

PI.  IV,  fig.  4. 
Not  Camptonectes?  e.rtenuatns  Meek  and  Haydeu,  1865:  Palteont.  Upper  Missouri, 

p.  78,  PI.  Ill,  fig.  6. 

This  species  is  more  slender  than  C.  hellistriatus,  the  height  from  beak 
to  base  being  considerably  greater  than  the  length,  and  it  is  apparently 
somewhat  more  convex.  The  sculpture  is  coarser  than  in  the  typical  form 
of  that  species,  Ijut  the  radiating  lines  are  somewhat  more  closely  arranged 
than  in  the  variety  dlstans.  The  most  important  difference,  however,  is  in 
the  ears,  which  in  the  left  valve  are  very  large  and  have  the  form  of  right- 
angled  triangles,  so  that  the  hinge  line  is  almost  as  long  as  the  greatest 
length  of  the  shell.  No  good  specimens  of  the  right  valve  have  been  seen, 
but  an  internal  cast  from  the  lower  canyon  of  the  Yellowstone  shows  that 
it  has  a  deep  byssal  sinus,  and  that  the  posterior  ear  is  nearly  rectangular, 
instead  of  having  the  very  oblique  form  seen  in  C.  hellistriatus.  From  C. 
])ertenuistriaius  this  species  may  be  easily  distinguished  by  its  much  coarser 
sculpture  and  by  differences  in  outline. 

The  specimen  figured  by  Whitfield  in  the  Geology  of  the  Black  Hills 
as  C.  extenuatus  is  clearly  identical  with  C.  platessiformis,  as  may  be  seen 


616     GEOLOGY  OF   THE  YELLOWSTONE  NATIONAL  PARK. 

bv  comparing'  the  two  specimens.  After  studying  the  types  of  C.  extemmtus 
I  can  see  no  reason  for  referring-  to  it  this  coarsely  sculptured  form,  which 
also  differs  in  outline.  As  has  already  been  stated,  the  types  of  C.  extenuatns 
are  unrecognizable  casts  in  sandstone,  showing  neither  the  sculpture  nor 
the  form  of  the  ears.  It  is  probably  either  C.  hellistriatiis  or  C.  pertenuistri- 
atus,  and  in  consideration  of  this  doubt  I  prefer  to  nse  the  later  name,  C. 
liertenuistriatus,  because  it  is  better  characterized. 

The  figured  specimens  of  C.  pkitessiformis  above  referred  to  came  from 
the  south  l)ase  of  Aquarius  Plateau,  southern  Utah,  and  east  of  Belle 
Fourche  River,  near  Bear  Lodge,  Black  Hills.  Those  in  the  present  collec- 
tion were  obtained  near  the  head  of  southeastern  valley  of  Fan  Creek; 
north  side  of  Fan  Creek  Pass;  top  of  hill  3  miles  southeast  of  Gravel  Peak, 
and  near  the  lower  canyon  of  the  Yellowstone. 

AviCULA    (OxVTOM.a)    WYOMINGEN.SIS    U.  Sp. 

Pteria   [O.rytoma)   munsteri    (Broun)    Meek    and    Haydeu,    1865:    TaLvont.     Upper 

Missouri,  p.  80,  tigs.  a-h. 
Pteria  or  Avicula  viucronata  Meek  and  Haydeu,  1805:  Ibid.,  p.  81,  suggested  name  for 

the  species  in  case  it  proves  distinct. 
Avicuhi  (Ojcytoma)  mitcroiutta  (M.  and  H.)  Whitfield,  1880:  Geol.  Black  Hills  Dakota, 

p.  357,  PI.  IV,  tigs.  1,  2. 
Not  Oxytoma  viucronata  (Meek)  Whiteaves,  1881:   Geol.  Surv.  Canada,  Mes.  Foss., 

Vol.  I,  pp.  238  and  251,  PI.  XXXI,  fig.  9,  PI.  XXX III,  lig.  (i. 
Not  Avicula  imicronata  Gabb,  1864:  PaliBout.  California,  Vol.  I,  p.  30,  PI.  V,  tig.  27. 

A  new  name  is  proposed  for  this  fairly  well  known  species  for  the  fol- 
lowing reasons.  In  Meek  and  Haj^den's  orighial  work  it  was  provisionally 
referred  to  A.  munsteri,  with  the  statement  that  it  would  probably  prove  to 
be  distinct,  and  if  so  it  should  be  named  Fieria  mucronata.  A  comparison 
with  figures  of  A.  munsteri  shows  that  they  are  not  identical  in  either  form 
or  sculpture,  and  later  authors  have  recognized  the  American  fossil  as  a 
distinct  species  under  Meek  and  Hayden's  suggested  name.  This  name 
can  not  lie  used  for  it,  however,  l^ecause  it  was  previously  applied  by  Gabb 
to  an  entirely  different  species  from  the  Triassic  of  California. 

The  fossil  from  the  Lower  Cretaceous  of  Queen  Charlotte  Islands 
referred  to  this  species  by  AVhiteaves  seems  to  me  to  be  specifically  distinct. 

The  collections  from  the  Yellowstone  National  Park  contain  only  two 
small  immature  specimens  from  the  foothills  at  the  base  of  north  slope  of 


MESUZOIC  FOSSILS.  617 

Flat  Moui\tain.  It  was  (irigiually  described  from  Wind  River  Valley, 
Wyoming-,  and  it  also  occurs  in  the  Black  Hills.  The  type  is  Meek's 
tig-ured  specimen.  No.  18il3,  United  States  National  Museum  collection. 

PSEUDOMONOTIS   CUHTA    (Hall)  ? 

AricUla  (?)  custa  Hall,  1852:   Stansbury's  Kept.  Gt.  Salt  Lake  Exp.,  p.  412,  PI.  IV, 

tigs.  1((,  h. 
Eumicrotis  curta  (Mall)  Meek  and  Ilayden,  1865:  Pala-ont.  Upper  Missouri,  p.  81, 

PI.  Ill,  figs.  10((-(/. 
Pseudomonoih  (Eumicrotis)  curta  (Hall)  Whitfield,  1880:  Geol.  Black  Hills  Dakota, 

p.  354,  PL  III,  figs.  20-25. 

A  single  imperfect  specimen  from  sunnnit  of  ridge  between  Red  and 
Basin  creeks  is  doubtfully  referred  to  this  species.  The  hinge  and  umbonal 
region  are  wanting,  and  the  identification  is  based  simply  on  general  form 
and  surface  sculpture  of  the  fragment.  The  species  is  abundant  in  the 
Jurassic  of  the  Black  Hills.  The  original  spelling  of  the  specific  name 
custa  seems  to  have  been  a  typographical  error  that  was  corrected  by  Meek, 
and  the  form  curta  has  since  been  followed. 

Gekvillia  montanaensis  Meek. 

GervUlia  montanaensis  Meek,  1873:  Ann.  Kept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  472. 
White,  1880:  Idem  for  IS 78,  p.  145,  PI.  XXXVII,  figs,  la  and  b. 

Distinguished  by  its  large  size  and  its  long  posterior  wing.  The 
types  are  from  near  the  lower  canyon  of  the  Yellowstone,  and  it  has  been 
collected  on  divide  between  Fawn  Creek  and  Gallatin  Valle}-;  east  side  of 
Fan  Creek  Pass;  Cinnabar  IMountain,  and  sunnnit  of  ridge  between  Red  and 
Basin  creeks,  near  Sheridan  Peak. 

GrERVILLIA  sp. 

A  smaller  and  much  more  slender  species  of  Gervillia  is  represented 
by  fragments  from  east  end  of  northeast  sjjur  from  Signal  Peak,  stream  Ijed 
west  of  Quadrant,  jr.,  and  saddle  in  ridge  west  of  south  head  of  Gardiner 
River. 

MoDioLA  suBiMBRicATA  Meek. 

MoiUola  (Vulsella)  suhimhricata  Meek,  1873:  Ann.  Eept.  TJ.  S.  Geol.  Surv.  Terr,  for 

1872,  p.  472. 
Volsella  suhimhricata  White,  18S0:  Idem  for  1878,  p.  145,  PI.  XXXVII,  figs.  2rt-c. 
This  species  seems  to  be  widespread,  but  not  very  abundant  at  any 


618  GEOLOGY  OF  THE  YELLOWSTOIS^E  NATIONAL  PAEK. 

place.     A  few  specimens  wei'e  obtained  on  divide  between  Fawn  Creek 

and  Gallatin  Vallev;  saddle  in  ridge  west  of  south  head  of  Gardiner ;  hills 

west  of  Snake  River  4  miles  south  of  second  crossing;  top  of  hill  3  miles 

southeast  of  Gravel  Peak;  ridge  between  Basin  and  Red  creeks,  and  slopes 

of  Mount  Sheridan. 

Pinna  king:  Meek. 

Pinna  Iclmji  Meek,  1877 :  U.  S.  Geol.  Expl.  40th  Parallel,  Vol.  IV,  Pt.  I,  p.  131 ,  PL 
XII,  ligs.  9,  9ft. 

A  few  fragments  of  this  species  were  obtained  iu  ridge  west  of  south 
liead  of  Gardiner,  and  on  north  side  of  old  road  between  Terrace  Moimtain 
and  Sentinel  Butte.     The  species  was  described  from  Weber  Canyon,  Utah. 

CucuLL.EA  HAGUF.i  Meek. 

PI.  LXXm,  fig.  1. 

Cucullcca  haguei  Meek,  1877 :  U.  S.  Geol.  Expl.  40tli  Parallel,  Vol.  IV,  Pt.  I,  p.  134, 
PI.  XII,  tigs.  1ft,  h. 

The  ty])e  of  the  species  came  from  Weber  Canyon,  Wasatch  Range, 
Utah.  In  Meek's  figure  the  radiating  striae  of  tlie  body  of  the  shell  are 
somewhat  exaggerated  and  the  concentric  lines  are  not  given  (|uite  as  nmch 
prominence  as  they  usually  have.  On  most  of  the  Yellowstone  National 
Park  specimens  the  radiating  lines  are  jjrominent  and  widely  separated  on 
the  anterior  third,  and  are  numerous  on  the  umbones,  but  all  excepting  the 
anterior  ones  usually  fade  out  before  reaching  the  middle  of  the  shell.  The 
fine,  regular,  closely  arranged  concentric  lines  cover  the  whole  valve. 

Some  of  the  casts  show  the  horizontal  teeth  at  both  ends  of  the  hinge 
line  characteristic  of  Cucullaea,  but  there  are  no  traces  of  the  ridge  bor- 
dering the  posterior  muscular  impression  that  is  seen  in  typical  species  of 
that  genus. 

The  specimen  figured  is  from  a  locality  near  Sentinel  Butte.  The 
species  is  also  represented  in  the  collection  from  north  side  of  Fan  Creek 
Pass;  saddle  in  ]-idge  west  of  south  head  of  Gardiner  River;  summit  of 
Avagon  road  between  Sentinel  Butte  and  Terrace  Mountain;  Cinnabar 
Mountain,  and  west  side  of  Snake  River  north  of  Berry  Creek. 

Trigonia  AMERICANA  Meek. 

Trigonia  americana  Meek,  1873:  Ann.  Kept.  U.  S.  (xeol.  Siuv.  Terr,  for  1872,  p.  472. 
White,  1880:  Idem  for  1878,  p.  148,  PI.  XXXVIII.  lig.  1ft,  I>. 

A  single  specimen  from  ridge  northwest  of  second  crossing  of  Snake 


MESOZOIC  FOaSlLS.  619 

River.     The  type  came  from  Spring-  Canyon  and  lower  canyon  of  the  Yel- 
lowstone, Montana. 

Trigonia  elegantissima  Meek. 

PI.  LXXIII,  fin.  2. 

Trigonia  elefjantinsima  Meek,  1873:  Ann.  Kept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  474. 

Shell  small,  subtrigonal  in  outline,  moderately  convex,  with  prominent, 
acute,  recurved  beaks;  posterior  umbonal  ridge  prominent,  ang-ular,  and 
curved;  anterior  end  brfjadly  rounded;  posterior  end  subangular  V)elow  at 
the  extremity  of  the  umbonal  ridge  and  forming  a  convex  slope  to  the  beak 
above;  escutcheon  not  distinctly  marked;  posterior  area  depressed  and 
bearing  numerous  equal,  fine,  radiating  lines;  remainder  of  surface  with 
regular,  closely  arranged,  small  concentric  ribs  that  show  a  tendency  to 
bend  downward  toward  the  front. 

Length  of  figured  specimen,  21  mm.;  height,  l-t  mm.;  convexity  of 
single  valve,  4  mm. 

This  species  is  closely  related  to  T.  americana,  from  which  it  differs  in 
outline,  and  more  especially  in  having  much  smaller  and  more  numerous 
concentric  ribs.  In  specimens  of  T.  americana  no  larger  than  the  type  of 
this  species  the  spaces  between  the  ribs  are  at  least  a  millimeter  wide. 

Meek's  original  description,  given  in  a  footnote  to  the  Hst  of  fossils 
from  Devils  Slide,  Cinnabar  Mountain,  Montana,  is  as  follows:  "A  small 
species  of  tlie  type  of  T.  costata,  but  having  the  concentric  or  horizontal 
costje  on  the  sides  of  the  valves  very  delicate,  closely  arranged,  and  but 
slightly  larger  than  the  radiating  ones  on  the  posterior  dorsal  region,  or 
corselet.  The  valves  are  rather  compressed,  about  one-fourth  longer  than 
wide,  and  have  the  posterior  umbonal  slopes  acutely  angular."  A  single 
valve  corresponding  to  this  description,  but  not  labeled,  is  in  the  original 
collection  from  Cinnabar  Mountain  studied  by  Meek,  and  this  is  probably 
his  type.  The  specimen  figured  was  collected  at  the  same  place  by  Mr 
W.  H.  Weed. 

Trigonia  montanaensis  Meek. 

Trigoma  montannensis  Meek,  1873:  Ann.  Kept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  472. 
White,  1880:  Idem  for  1878,  p.  247,  PI.  XXXVIII,  fig.  2a. 

The  types  are  from  the  locality  near  the  lower  canyon  of  the  Yellow- 
stone.    A  few  specimens  were  obtained  1  mile  from   Swan  Lake  Valley, 


620     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

north  of  old  road  to  Mammoth  Hct  Springs;  Cinnabar  Mountain;  saddle  in 
rid"-e  west  of  south  branch  of  Gardiner  River;  south  sloi^e  of  ridg-e  south 
of  Gray  Mountain,  and  east  end  of  northeast  s})ur  from  Signal  Peak. 

ASTARTE    MEEKI    n.  Sp. 

PL  LXXIJI,  figs.  3-5. 

Shell  of  medium  size,  subcircular  in  outline,  moderately  convex ;  beaks 
prominent,  median  in  position ;  dorsal  margin  descending  rajndly  from  the 
beaks,  with  a  convex  curve  behind  and  slightly  excavated  in  front;  anterior, 
posterior,  and  ^-entral  margins  forming  a  regular  curve ;'  surface  marked  by 
numerous  fine,  regular,  concentric  costse.     Margin  crenulate  within. 

One  of  the  types,  an  average-sized  specimen,  has  the  following  dimen- 
sions: Length,  l(i  mm.;  height,  14  nun.;  convexity  of  single  valve,  about  3 
mm.  The  largest  specimen  in  the  collection  is  23  mm.  in  length  and  20 
mm.  in  height.  Associated  with  these  there  are  several  more  elongated 
shells,  one  of  which  is  figured,  that  I  was  at  first  inclined  to  regard  as  a 
distinct  species,  but  it  is  probable  that  the  difference  ii>  form  is  due  to  dis- 
tortion by  pressure. 

Compared  with  Astarte  pachardi  White  this  species  is  proportionally 
somewhat  more  elongate,  less  convex,  and  the  concentric  sculpture  is  much 
finer  and  more  regular.  The  species  was  first  noticed  by  Meek,  who  men- 
tioned it  as  "Astarte  (?)"  in  a  list  of  Jurassic  fossils  collected  by  Dr.  Peale 
near  the  lower  canyon  of  the  Yellowstone.^  It  occurs  in  the  collections 
from  head  of  Gardiner,  Sentinel  Butte,  Cinnabar  Mountain,  west  side  of 
Snake  River  north  of  Berry  Creek. 

Astarte  sp. 

Another  species  of  Astarte  is  represented  by  fragmentary  specimens 
which  show  the  specific  features  fairly  well,  Ixit  as  they  are  not  sufficient 
for  a  good  illustration  the  species  has  not  been  named.  It  is  a  very 
elongate  form,  with  strong,  regular,  concentric  ridges.  In  its  younger 
stages,  as  shown  by  the  lines  of  growth,  it  is  a  short  subtriangular  form, 
but  later  it  rapidly  increases  in  length  and  the  posterior  end  becomes 
obliquely  truncate.  It  occurs  on  the  divide  at  head  of  Fawn  Creek, 
Sentinel  Butte,  Cinnabar  Mountain,  and  near  lower  canyon  of  Yellowstone 
River. 

lAnu.  Kept.  U.  S.  Oeol.  Surv.  Terr,  for  1872,  p.  472. 


MESOZOIG  FOSSILS.  621 

TaNCREDIA  ?    KNOWLTONr   11.   sp. 
PI.  LXXIII,  (iff.  (i. 

Shell  small,  obliquely  snbovate  in  outline;  beaks  prominent,  sub- 
median;  (lor.sal  margin  behind  the  beaks  descending-  rapidly  to  the  broadly 
rounded  posterior  end,  which  is  most  i)r<iminent  below;  anterior  end 
rounded,  most  prominent  above,  somewhat  more  narrow  than  the  posterior 
end;  ventral  margin  gently  convex;  posterior  umbonal  ridge  with  a 
tendency  to  become  angular;   surface  marked  by  tine  lines  of  growth. 

Length,  15  mm.;  height,  12  mm.;  convexity  of  single  valve,  about  2  mm. 

The  hinge  is  unknown  and  the  generic  reference  is  based  merely  on 
external  form.  The  species  seems  to  be  congeneric  with  the  species  from 
the  Black  Hills  referred  to  Tancredia  by  Whittield,  though  the  difference 
in  outline  prevents  its  reference  to  any  of  his  species. 

From  shales  on  north  side  of  road  near  Sentinel  Bvitte,  collected  by 
Prof.  F.  H.  Knowlton. 

Protocardia  shumardi  Meek  and  Hayden. 

Cardium,  shumardi  Meek  and  Hayden,  18G0:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  182. 
Protocardia  shumardi  Meek   and  Hayden,  1865:  Pahiiont.     Upper  Missouri,  p.  98, 
figs,  A  and  B  in  text. 

The  collection  contains  several  specimens  of  a  small  Protocardia  that 
seem  to  belong  to  this  Black  Hills  Jurassic  species.  They  have  the  out- 
lines of  that  species,  though  some  of  the  shells  are  nearly  twice  as  large  as 
the  figure  of  the  type.  The  body  of  the  valve  is  marked  only  by  fine 
lines  of  growth,  and  the  posterior  area  bears  about  eight  to  twelve  radiating 
ribs  that  are  broader  than  the  interspaces. 

Collected  on  the  divide  between  Fawn  Creek  and  Grallatin  Valley; 
head  of  north  fork  of  Fawn  Creek ;  Sentinel  Butte,  and  Cinnabar  Mountain. 

Cyprina?  cinnabarensis  n.  sp. 
PI.  LXXIII,  flg.s.  7  and  8. 

Shell  of  medium  size,  moderately  convex,  subcircular  in  outline,  with 
prominent  submedian  beaks;  dorsal  margin  excavated  in  front  of  the  beaks, 
gently  sloping  behind,  and  in  both  cases  passing  gradually  into  the  rounded 
ends;  posterior  end  in  some  individuals  slightly  straightened,  so  as  to  become 


622     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

almost  vertically  subtruncate;  ventral  margin  broadly  rounded;  surface 
sculpture  unknown.  There  is  a  ^s-ery  obscure  posterior  umboiial  ridge,  and 
the  muscular  and  pallial  impressions  are  not  clearly  shown  on  the  cast. 

One  cast  sliowing  impression  of  part  of  hinge  has  three  strong  cardinal 
teeth,  of  which  the  posterior  one  is  very  long  and  olilique.  The  specimen 
is  not  in  condition  to  show  Avhether  lateral  teeth  are  present. 

Height  of  an  average  shell,  28  mm.;  length,  32  mm.;  convexity  of  two 
valves  united,  15  mm.  The  largest  specimens  in  the  collection  have  the 
corresponding  dimensions  about  one-fifth  greater. 

The  onlv  described  American  Jurassic  species  with  Avliich  this  need  be 
compared  is  Dosinia  jurassica  Whitfield,  which  is  a  smaller,  more  convex 
species,  with  less  prominent  beaks  and  sliglit  differences  in  outline.  It  is 
not  probable  that  the  two  sjiecies  are  closely  related. 

Collected  from  Cinnabar  Slountain;  divide  between  Fawn  Creek  and 
Gallatin  Valley;  east  end  of  northeast  spur  from  Signal  Peak;  saddle  in 
rido-e  west  of  south  head  of  Gardiner  River;  head  of  Fawn  Creek  northeast 
of  Monument  Peak,  and  ridge  between  Basin  and  Red  creeks,  near  Sheridan 
Peak. 

Cyprina?  iddingsi  n.  sp. 

PI.  LXXIir,  fig.  9. 

Shell  small,  convex,  suboval  in  outline;  beaks  rather  prominent,  sub- 
median;  dorsal  margin  sloping  gently  from  the  beak  to  the  posterior  end, 
slightly  excavated  in  front  of  the  beak  and  descending  rather  more  rapidl)-; 
anterior  and  posterior  ends  broadly  and  almost  equally  rounded;  ventral 
margin  gently  convex;  posterior  umbonal  slope  with  a  subangular  ridge 
extending  from  the  beak  to  the  postero-basal  margin;  surface  with  oljscure 
lines  of  growth  and  a.  few  irregular  concentric  undulations  near  the  free 

Length  of  largest  sjiecimen,  24.5  mm.;  height,  18.5  mm.;  convexity  of 
both  valves,  about  12  mm. 

This  species  differs  from  C.  cinnabarensis  in  its  smaller  size,  proportion- 
allv  greater  convexity,  more  elongate  form,  narrower  posterior  end,  less 
prominent  beaks,  and  more  distinct  umbonal  ridge.  Its  generic  position  is 
doubtful,  us  its  hinge  characters  are  entirel}'  uidcnown. 

From  saddle  at  head  of  Fawn  Creek  northeast  of  Monument  Peak, 


MESOZOIC  FOSSILS. 


(523 


and  (tlie  type)  from  west  end  of  ridge  southeast  of  mouth  of  Mink  Creek, 
where  it  was  collected  by  Professor  Iildings. 

Cypricardia  ?  HAGUKi  n.  sp. 

PL  LXXIII,  figs.  11-13. 

Shell  large,  inflated,  subt^uadrate  in  outline;  beaks  very  prominent, 
strongly  curved  inward  and  forward,  approximate,  and  projecting  far 
beyond  the  hinge  line;  posterior  umbonal  slope  with  a  prominent  angular 
ridge  descending  from  the  beak  to  the  postero-basal  angle  and  dividing  the 
sui-face  of  the  .shell  into  two  distinct  areas,  of  which  the  posterior  is 
obliquely  flattened,  while  the  rest  of  the  shell  is  jiretty  evenh^  convex; 
dorsal  margin,  exclusive  of  beaks,  gently  descending  behind  and  excavated 
in  front;  anterior  end  broadly  rounded;  posterior  end  oljliquely  truncate; 
ventral  margin  almost  straight ;  surface  sculpture  not  known,  luit  probably 
consisting  only  of  lines  of  growth. 

The  two  figured  specimens,  both  of  which  are  probably  somewhat 
distorted  in  difterent  directions,  give  the  following  measurements: 


Length. 

Height. 

Convexity 
of  both" 
val\es. 

vim. 
52 

6.T 

■mm. 
49 
.52 

mm. 
40 
40 

The  sliorter  specimen  is  more  nearly  of  normal  proportions  than  the 
other. 

The  species  is  represented  )jy  about  twenty-five  specimens,  all  of  which 
are  internal  casts,  and,  as  the  details  of  the  hinge  have  not  been  satisfactorilv 
made  out,  the  generic  reference  is  only  provisional.  Imjjressions  of  a  part 
of  the  hinge  show  the  presence  of  two  or  three  strong  cardinal  teeth  and 
make  it  reasonably  certain  that  the  shell  belongs  to  the  Cyprinida?.  The 
casts  also  show  the  adductor  muscular  impressions  and  the  pallial  line.  The 
anterior  scar  is  rather  large,  semilunar,  and  (on  the  cast)  much  elevated, 
while  the  posterior  one  is  somewhat  smaller  and  scarcely  at  all  elevated. 

There  are  no  American  species  with  which  this  need  be  compared,  but 
Cypricardia  hathonica  d'Orb.,  as  figured  by  Morris  and  Lvcett  in  Mollusca 


624     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

of  the  Great  Oolite,  Pt.  II,  p.  75,  PL  VII,  tig.  8,  seems  to  be  a  closely 
related  form. 

It  occurs  at  east  end  of  northeast  spur  frou;  Signal  Peak;  saddle  in 
ridge  west  of  south  branch  of  liead  of  Gardiner;  head  of  Fawn  Creek 
northeast  of  Monument  Peak  and  Cinnabar  Mountain.  Specimens  collected 
by  Dr.  Peale  at  Devils  Slide,  Cinnabar  ]\Iountain,  were  labeled  and  listed 
by  Meek'  as  "Cucullrea." 

Pholadomya  kingi  Meek. 
PL  LXXIV,  figs.  1-3. 

Pholadomya  Mnyi  Meek,  1873:   Ann.  Kept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  473, 
White,  1880:  Idem  for  1878,  p.  150,  PI.  XXXVIIl,  tigs,  a  and  h. 

This  abundant  species  varies  considerably  in  sculpture,  and  the  fact 
that  almost  every  specimen  in  the  collection  is  distorted  in  various  ways  by 
pressure  causes  it  to  appear  nmcli  more  variable  in  both  form  and  sculpture 
than  it  really  is. 

The  type  specimen  figured  by  White,  which  is  itself  somewhat  distorted, 
has  eleven  radiating  costfe  on  the  central  region  of  the  ^alve,  though  they 
are  not  quite  so  prominent  as  they  are  represented  in  the  drawing  above 
referred  to.  Most  of  the  specimens  from  the  Park  have  fewer  (usually  not 
more  than  eight  or  nine)  costre,  and  on  flattened  specimens  these  are  some- 
times barely  visible. 

Fholadoinyn  ncvadana  Gabb,  from  the  Lias  of  Volcano,  Nevada,  is  evi- 
dently a  related  species,  and  Professor  Hyatt Mias  treated  P.  k'mgi  as  a  syno- 
nvm  of  it.  Compared  with  Gabb's  figure  and  description,  however,  P.  k'mfii 
is  smaller  and  more  slender  and  has  the  beaks  farther  from  the  anterior  end. 
The  costse  also  are  differently  arranged.  Professor  Hyatt  has  compared 
tor  me  specimens  of  the  Yellowstone  form  with  those  from  California 
referred  to  P.  ncvadana,  and  he  is  now  inclined  to  regard  them  as  distinct. 
It  is  at  least  safer  to  keep  them  separate  until  direct  comparison  can  be 
made  with  Gabb's  type,  which  seems  to  be  lost,  or  with  specimens  from  the 

original  locality. 

The  species  occur  in  the  collection  from  divide  between  Fawn  Creek 
and  Gallatin  Valley;  east  end  of  northeast  spur  from  Signal  Peak;  saddle 

'  Anu.  Kept.  U.  S.  Geol.  S-iv.  Teir.  for  lS-2,  ]>.  474.  ■  Biil.  Geo).  Soc.  Am.,  Vol.  \.  p.  418. 


MESOZOIC  FOSSILS,  625 

ill  ridg-o  west  of  south  branch  head  of  Gardiner;    head  of  Fawn  Creek  north- 
east of  Mouuineut  Peak,  Cinnabar  Mountain. 

I'lIULADOMYA    INjEQUIPLICATA    11.  SJl. 

PI.  LXXIV,  fig.  4, 

Ct'.  PhoJadomija  multilineata  Gabb,  18(59:  Am.  Jour.  Coucbology,  Vol.  V,  p.  10,  PI.  V, 
fig.  <>. 

Shell  small,  ventricose,  elongate  suboval  in  outline,  with  prominent 
approximate  beaks  situated  near  the  anterior  end;  anterior  and  ventral  mar- 
gins forming  a  nearly  regular  curve,  which  is  most  prominent  a  little  behind 
the  middle;  posterior  end  rounded,  slightly  subtruncate  above;  surface 
marked  b}'  about  twenty  radiating  costse  that  vary  both  in  size  and  in  dis- 
tance from  each  other  and  cover  the  whole  valve,  excepting  a  very  small 
space  in  front  and  a  larger  one  in  the  postero-dorsal  region. 

Length,  39  mm.;  height,  31  mm.;   convexity  of  both  valves,  24  mm. 

Pholadomya  multilineata,  which  is  associated  with  P.  mvadana,  seems  to 
be  about  as  closely  related  to  this  species  as  P.  nevadana  is  to  P.  Ungi.  P. 
multilineata  is  larger  than  P.  incequipUcata,  has  more  numerous  costae  (about 
thirty,  according  to  Gabb),  and  is  more  angular  at  the  posterior  end,  besides 
differing  somewhat  in  other  details  of  outline. 

Only  a  few  specimens  were  collected  on  divide  between  Fawn  Creek 
and  Gallatin  Valley,  where  it  is  associated  with  P.  Ungi. 

HOMOMYA    GALLATINENSIS    11.  Sp. 
PI.  LXXIV,  figs.  6  and  7. 

Shell  of  medium  size,  oblong  subcylindrical ;  beaks  rather  prominent, 
incurved,  approximate,  and  situated  near  the  anterior  end  of  the  shell; 
dorsal  margin  in  front  of  the  beaks  declining  rapidly  to  the  broadly  rounded 
anterior  end,  which  passes  by  a  gentle  curve  into  the  nearly  straight  dorsal 
margin.  Surface  marked  by  lines  of  growth  and  irregular  concentric 
undulations.     The  posterior  end  gapes  slightly. 

Length,  85  mm.;   height,  42  mm.;   convexity  of  both  valves,  36  mm. 

This  species  apparently  belongs  to  the  subgenus  Homomya  as  detined 
in  Zittel's  Handbuch  der  Palseontologie,  but  Fischer  does  not  recognize  the 
group  and  divides  the  species  that  have  been  referred  to  it  between  Arcomya 
and  Pleuromya.     The  specimens  from  Yellowstone  National  Park  do  not 

MON  XXXII,  PT  II 40 


626     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

show  the  structure  of  the  hinge  nor  other  details  of  the  interior  that  are 
used  as  generic  characters. 

The  type  is  from  the  divide  between  Fawn  Creek  and  Gallatin  Valley. 
The  species  is  represented  by  nine  other  examples  from  Fan  Creek  Pass, 
head  of  Gardiner ;  saddle  in  ridge  west  of  south  branch  of  head  of  Gar- 
diner; head  of  Fawn  Creek  northeast  of  Monument  Peak,  and  Cinnabar 
Mountain. 

Pleuromya  subcompressa  Meek. 

P].  LXXIY,  figs.  8-11. 

Myacites  {Pleuromya)  subcompressa  Meek,  1873:  Anu.  Rept.  IT.  S.  Geol.  Sarv.  Terr. 

for  1872,  p.  472.     1877:  U.  S.  Geol.  Expl.  40tli  Parallel,  Yol.  lY,  Pt.  I,  p.  136, 

PI.  XII,  figs.  6,  6a. 
Myacites  subcompressus  (Meek)  White,  1880 :  Anu.  Rept.  U.  S.  Geol.  Surv.Terr.  for  1878, 

p.  151,  PI.  XXXYIII,  figs,  5a-e. 

This  most  abundant  species,  which  was  originally  described  from 
Weber  Canyon,  Utah,  is  represented  by  several  hundred  specimens,  from 
everj'  Jurassic  locality  in  the  Park  region  at  which  fossils  were  collected 
from  the  lower  argillaceous  limestone  and  shale.  Almost  every  specimen  is 
more  or  less  distorted,  and  everj^  variation  in  form  is  seen  that  a  thin-shelled 
elongate  species  can  be  made  to  assume  when  embedded  in  soft  strata  and 
subjected  to  pressure.  In  addition  to  these  accidental  distortions,  it  is  evi- 
dent that  the  species  is  naturally  quite  variable  in  both  form  and  sculpture, 
some  individuals  being  nearly  smooth  while  others  are  marked  by  rather 
strong  concentric  plications.  Extreme  variations  approach  the  plicate  ' 
Pleuromya  iveherensis  Meek  on  the  one  hand  and  the  nearly  smooth  elongate 
Pleuromya  newtoni  Whitfield  on  the  other.  The  extent  and  directions  of  vari- 
ation are  fairly  well  shown  by  Wliite's  figures  above  cited,  though  some  of 
these  forms  are  slightly  modified  b)^  pressure. 

Single  specimens  representing  three  or  four  extreme  varieties  could  be 
selected  that  if  taken  alone  might  be  regarded  as  distinct  species,  but  when 
the  attempt  is  made  to  classify  the  entire  large  collection  coming  from 
practically  one  horizon  and  a  limited  area,  it  is  found  that  none  of  the  dis- 
tinctions will  hold  good. 

The  specimens  figured  show  some  of  the  principal  variations  in  form, 
and  were  selected  from  those  apparently  least  modified  by  accidental  dis- 
tortion.    They  are  from  Fan  Creek  Pass,  divide  between  Fawn  Creek  and 


MESOZOIO  FOSSILS. 


627 


Gallatin  Valley,  hills  west  of  Snake  River  4  miles  south  of  second  crossing, 
and  Cinnabar  Mountain. 

The  general  custom  ^f  recent  authors  is  followed  in  using  the  name 
Pleuromya  instead  of  Myacites. 

Thracia  weedi  n.  sp. 
PI.  LXXV.  figs.  1-3. 

Shell  of  medium  size,  thin,  compressed,  elongate,  subelliptical  in  out- 
line; beaks  rather  prominent,  submedian;  dorsal  margin  sloping  rather 
rapidly  and  almost  equally  before  and  behind  the  beaks;  anterior  end 
broadly  rounded,  most  prominent  below;  posterior  end  subtruucate;  ventral 
margin  slightly  convex,  somewhat  sinuous  toward  the  posterior  end;  poste- 
rior umbonal  ridge  narrow  and  sharply  defined;  surface  marked  by  irreg- 
ular concentric  undulations  and  by  numerous  fine  lines  of  growth. 

The  specimens  selected  for  illustration,  which  are  of  average  size,  have 
the  following  dimensions,  respectively: 


Length. 

Height. 

Convexity 
of  both 
valves. 

mvi. 
29 
26 
34 

mm. 
19 
18 
20 

mm. 
4 
5 
5 

All  the  examples  in  the  collection  have  suffered  more  or  less  accidental 
compression  and  distortion  in  the  rocks,  so  that  they  show  considerable  vari- 
ation in  outline,  and  probably  on  account  of  this  compression  they  do  not 
show  the  posterior  gape  that  they  should  have  if  they  really  belong  to  the 
genus  Thracia. 

The  species  diff'ers  too  much  in  outline  and  proportions  from  tlie  two 
forms  of  Thracia  (?)  described  from  the  Jurassic  of  the  Black  Hills  to 
require  detailed  comparison. 

The  types  are  from  stream  bed  west  of  Little  Quadi-ant  Mountain 
and  from  saddle  in  ridge  west  of  south  head  of  Gardiner  River.  Other 
specimens  were  collected  at  head  of  Fawn  Creek,  northeast  of  Monument 
Peak. 


628     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Thbacia?  montanaensis  (Meek)'? 

PL  LXXIII,  fig.  10. 

Gorimya  montanaensis  Meek,  1873 :  Ann.  Rept.  U.  S.  GeoL  Surv.  Terr,  for  1872,  p.  474. 

Shell  small,  subquadrate  in  outline,  convex,  with  prominent  beak  situ- 
ated a  little  in  advance  of  the  middle;  dorsal  margin  nearly  straight, 
declining  slightly  on  each  side  of  the  beak;  anterior  end  broadly  rounded, 
forming  almost  a  right  angle  with  the  dorsal  margin  above,  and  uniting 
with  the  convex  ventral  mai-gin  below  by  a  regular  curve;  posterior  end 
obliquely  truncate;  posterior  umbonal  ridge  subangular  and  accompanied 
by  a  narrow  depressed  area  or  groove ;  surface  marked  by  lines  of  growth. 

Length,  17  mm.;  height,  14  ram.;   convexity  of  single  valve,  4  mm. 

The  above  description  is  drawn  from  a  single  valve  from  "Devils 
Slide,  Cinnabar  Mountain,  Yellow^stoue  River,"  which  may  be  the  original 
type  named  by  Meek  in  the  report  above  referred  to,  though  it  was  not 
labeled  by  him.  It  was  named  in  a  list  of  fossils  from  this  locality,  with  a 
footnote  saying  that  "This  is  very  similar  to  some  varieties  of  C.  glabra 
Agassiz,  but  it  is  a  smaller,  proportionately  shorter,  and  more  convex  shell, 
with  the  anterior  margins  just  in  front  of  the  beak  more  excavated." 

Anatina  (Cercomya)  punctata  n.  sp. 
PI.  LXXIV,  fig  5. 
Shell  of  medium  size,  not  so  slender  as  the  typical  forms  of  the  sub- 
genus; beak  prominent,  somewhat  in  advance  of  the  middle  of  the  shell, 
directed  backward;  dorsal  margin  almost  straight  and  descending  slightly 
in  front  of  the  beaks,  concave  behind;  anterior  end  broadly  rounded,  sub- 
angular  above;  posterior  end  much  more  narrow  and  rounded,  ventral 
margin  slightly  sinuous;  surface  of  the  shell  divided  into  two  distinct  areas 
by  a  narrow  well-defined  groove  that  descends  almost  vertically'  from  the 
beak  to  the  ventral  margin;  anterior  area  marked  by  broad  concentric 
ridges  and  sulcations  and  by  very  fine  lines  of  growth,  the  latter  continuing 
over  the  posterior  area;  middle  third  of  the  posterior  area  slightly  more 
convex  and  prominent  than  the  rest  and  bearing  about  nine  distinct  granu- 
lar radiating  lines.  In  addition  to  this  sculpture,  which  is  seen  on  internal 
casts,  a  mold  of  the  exterior  of  the  shell  shows  that  the  entire  surface  bears 
radiating  lines  of  minute  tubercles, which  are  most  prominent  on  the  posterior 


MESOZOIO  FOSSILS.  629 

area,  and  give  the  punctate  appearance  that  suggested  the  specific  name, 
though  it  can  liardly  be  considered  a  specific  character,  since  it  is  common 
in  this  and  related  genera. 

The  species  is  represented  by  three  imperfect  A^alves  from  the  divide 
between  Fawn  Creek  and  GaUatiu  Valley,  south  slope  of  ridge  south  of 
Gray  Mountain,  and  west  side  of  Snake  River  north  of  Berry  Creek.  The 
specimen  figured,  which  is  from  the  second  locality  mentioned,  measures 
39  mm.  in  length  and  19  nun.  in  height. 

In  the  well-defined  radiating  lines  of  the  posterior  area  this  species 
resembles  the  Upper  Cretaceous  forms  to  which  Conrad  gave  the  name 
Anatimya. 

Anatina  (Cercomya)  sp. 

Another  species  of  this  genus  is  represented  by  a  single  specimen  from 
the  east  side  of  Fan  Creek  Pass,  which  is  too  imperfect  for  illustration  and 
full  description.  It  is  much  larger  than  A.  punctata,  measuring  76  mm.  in 
length,  and  it  differs  from  that  species  in  the  outline  of  the  anterior  end  and 
in  the  entire  absence  of  radiating  lines  on  the  posterior  area. 

GASTROPODA. 

Neritina  wyomingensis  n.  sp. 
PI.  LXXV,  figs.  4  and  5. 

Shell  small,  consisting  of  about  two  and  a  half  or  three  rapidly 
increasing  volutions  ;  spire  very  low  and  inconspicuous  ;  last  whorl  slightly 
shouldered  and  forming  about  nine-tenths  of  the  visible  bulk  of  the  shell ; 
surface  smooth,  with  rather  distinct  lines  of  growth  near  the  aperture, 
which  has  the  thin  sharp  outer  lip  and  straight  inner  lip  with  broad  flat- 
tened columella  characteristic  of  the  genus.  The  inner  lip  is  smooth,  or 
nearly  so,  but  the  specimens  are  not  in  condition  to  show  whether  it  bears 
minute  denticulations. 

Height  of  the  type,  6  mm.;  greatest  breadth,  6  J  mm. 

This  species  has  a  superficial  resemblance  to  Neritina?  pTiaseolaris 
"White  from  the  Jurassic  of  Utah,  but,  besides  slight  ditferences  in  form,  the 
columella  in  that  species  is  not  flattened  and  the  inner  lip  is  not  straight,  so 
that  it  has  been  referred  to  Lyosoma. 

The  only  other  described  American  Jurassic  Neritina  is  N.  nebraseensis 


630  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

M.  and  H.,  which  is  much  larger  and  more  slender  in  form,  differing  in  all 

its  details  from  this  species,  which  is  somewhat  similar  in  form  and  size  to 

Neritina  xyisum  Meek  from  the  Upper  Cretaceous  of  Utah. 

The  type  was  collected  by  Prof.  A.  C.  Gill  about  3  miles  southeast  of 

Gravel  Peak. 

Lysoma  powelli  White. 

Neritina  poioelli  White,  1876:  Geol.  Uinta  Mountains,  p.  110. 

Lyosoma  powelli  White,  ISSO:  Ann.  Rept.  U.  S.  Geol.  Sarv.  Terr,  for  1878,  p.  153,  PI. 
XXXVllI,  figs.  6a-d. 

One  well-preserved  specimen  was  obtained  on  saddle  at  head  of  Fawn 
Creek,  northeast  of  Monument  Peak,  and  another  on  ridge  south  of  Mammoth 
Hot  Springs,  on  main  terrace.  The  species  has  not  before  been  reported 
from  any  locality  excepting  at  the  mouth  of  Thistle  Creek,  Spanish  Fork 
Canyon,  Utah. 

Both  Zittel  and  Fischer  are  inclined  to  make  Lyosoma  a  synonym  of 
Otostoma  d'Archiac,  an  Upper  Cretaceous  subgenus  of  Nerita,  but  Lyosoma 
really  has  the  thin  inner  lip  without  any  callus  or  flattening  of  the  columella, 
while  the  Cretaceous  form  has  been  shown  to  have  the  characteristics  of 
Neritina  in  these  respects. 

TUKRITELLA    Sp. 

A  single  small  specimen  from  3  miles  southeast  of  Gravel  Peak  has 
the  form  of  this  genus,  but  is  insufficient  for  specific  description.  It  con- 
sists of  six  flattened  whorls  with  channeled  sutures. 

NaticaI  sp. 

A  naticoid  form  is  represented  by  imperfect  internal  casts  from  Fan 
Creek  Pass,  saddle  west  of  south  head  of  Gardiner,  head  of  Fawn  Creek 
northeast  of  Monument  Peak,  and  near  Sentinel  Butte. 

It  is  probably  undescribed,  being  very  much  larger  than  Natica  1  lelia 
Hall  and  Whitfield,  which  is  the  only  described  naticoid  shell  from  the 
Jurassic  of  this  western  interior  region. 

CEPHALOPODA. 
OppeliaI  sp. 

Ammonites  are  rare  in  the  Yellowstone  National  Park  collection,  and 
the  few  that  were  obtained  are  too  fragmentary  and  badly  preserved  for 
accurate  classification. 

One  species  is  represented  by,  two  flattened  specimens,  about  3  inches 


MESOZOIC  FOSSILS.  631 

in  diameter,  from  the  divide  between  Fawn  Creek  and  Gallatin  Valley. 
This  is  a  nearly  smooth,  discoid,  involute  form,  with  narrow  umbilicus  and 
rounded  abdomen.  The  outer  two-thirds  of  the  body  whorl  appears  to 
have  been  entirely  smooth.  On  the  other  third  the  abdomen  is  crossed  by 
small  ribs,  giving  it  almost  a  dentate  outline;  and  on  earlier  stages  these  ribs 
are  relatively  longer  and  more  prominent,  passing  nearly  halfway  across 
the  flanks  of  the  shell.  In  general  form  and  sculpture  this  species  resembles 
Oppelia  suhpUcatella  Vacek,^  from  the  Oolitic  of  Cap  San  Vigilio.  The 
septa  are  not  preserved. 

Fragments  of  larger  individuals  that  may  belong  to  the  same  species 
were  obtained  on  Fan  Creek  Pass,  saddle  in  ridge  west  of  south  head  of 
Gardiner,  and  from  Cinnabar  Mountain.  They  are  less  compressed  than 
the  specimens  above  described,  but  with  the  material  at  hand  it  is  impos- 
sible to  determine  whether  this  difference  is  due  to  accidental  distortion. 
Some  of  the  fragments  show  strong  plications  on  the  abdomen.  A  large 
specimen,  8  inches  in  diameter,  from  limestone  on  ridge  south  of  Sheridan 
Peak,  appears  to  be  related  to  the  forms  above  mentioned,  though  it  is 
somewhat  more  involute,  and  is  so  much  weathered  that  all  the  surface 
characters  and  the  iiner  subdivisions  of  the  septa  have  disappeared.  The 
specimen  is  septate  throughout.  The  septa  appear  not  to  have  been  very 
complex  and  the  lateral  saddles  are  very  broad.  It  is  possible  that  this 
specimen  should  be  referred  to  Ammonites  henryi  M.  and  H.,  which  it  some- 
what resembles  both  in  general  form  and  in  the  septa. 

Perisphinctes  sp. 
Collections  obtained  by  Dr.  Peale  near  the  lower  canyon  of  the 
Yellowstone  contain  fragments  of  two  species  of  Ammonites  that  probably 
belong  to  Perisphinctes,  judging  from  the  sculpture.  Fragments  of  one  of 
these  species  were  also  obtained  on  saddle  in  ridge  west  of  south  head  of 
Gardiner  River. 

Belemnites  densus  Meek  and  Hayden. 

Belemnites  densus  Meek  and  Hayden,  1858:  Proc.  Acad.  ^at.  Sci.  Phila.,  p.  58.  1865: 

PalJEont.  Upper  Missouri,  p.  126,  PI.  IV,  figs.  lOa-c;  PI.  V,  figs.  la-i.  Meek, 

1876 :  Simpson's  Kept.  Expl.  Great  Basin,  Utah,  p.  358,  PL  III;  figs.  4a,  b.  Whit- 
field, 1880:  GeoL  Black  Hills  Dakota,  p.  381,  PL  VI,  figs.  15-19. 

This  species,  which  is  abundant  in  the  Jurassic  of  the  Black  Hills  and 

'  AbhancU.  K.-k.  geol.  Reiclisaustalt,  Vol.  XII,  p.  82,  PI.  XI,  figs.  1-5,  1886. 


632  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

various  localities  in  Wyoming,  is  represented  in  the  Yellowstone  National 
Park  collection  by  only  a  few  specimens,  from  saddle  in  ridge  west  of  south 
head  of  Gardiner;  west  of  Snake  River  4  miles  south  of  second  crossing 
and  3  miles  south  of  mouth  of  Glade  Creek. 

CRETACEOUS   SPECIES. 

DAKOTA  (1)  FORMATION.' 
PELECYPODA. 

Unio  sp.  undet. 

Several  casts  of  a  small  species  of  Unio  were  collected  with  the  gastro- 
pods named  below  in  Three  Forks  Valley,  Montana,  and  on  Fawn  Creek 
Plateau.  The  species  is  doubtless  new,  but  the  material  is  insufficient  for 
description. 

GASTROPODA. 

GONIOBASIS!    PEALEI    U.  Sp. 
PI.  LXXV,  fig.  6. 

Shell  small,  slender,  CiOngate,  consisting  of  about  eight  convex  whorls; 
apex  of  spire  acute;  upper  third  of  each  whorl  slightly  flattened,  so  tliat  it 
is  most  prominent  below  the  middle;  suture  hnear,  deeply  impressed; 
surface  nearly  smooth,  being  marked  only  by  fine  lines  of  growth,  and  on 
some  specimens  by  faint  indications  of  spiral  lines.  The  full  form  of  the 
aperture  is  not  shoAvn  on  any  of  the  specimens,  but  it  appears  to  have  been 
suboval  and  slightly  produced  in  front.     Shell  apparently  not  umbilicated. 

Length  of  an  average  specimen  with  eight  whorls,  14  mm.;  breadth  of 
body  whorl,  7  mm. 

This  species  is  very  doubtfully  referred  to  Goniobasis,  though  it  seems 
to  be  related  to  G.  gracilenta  Meek,  from  the  Judith  River  beds.  In  general 
aspect  and  in  the  form  of  the  whorls  it  resembles  some  recent  species  of 
Pomatiopsis,  but  the  form  of  the  aperture  and  the  absence  of  an  umbilicus 
separate  it  from  that  genus. 

The  specimen  figured  was  collected  by  Dr.  A.  C.  Peale  in  Three  Forks 

'  See  remarks  on  pp.  604-605. 


MESOZOIC  FOSSILS.  633 

Valley,  Montana  Other  examples  were  obtained  in  the  Gallatin  Range 
anil  at  several  points  in  the  northwestern  part  of  Yellowstone  National  Park 
from  fresh-water  beds  of  the  Cretaceous  section  of  that  region. 

GONIOBASIS?    INCREBESCENS    n.  sp. 
PI.  LXXV,  fig.  7. 

Shell  of  about  the  same  length  as  the  preceding,  but  more  robust 
in  form,  consisting  of  only  about  five  rapidly  increasing  convex  whorls; 
surface  nearly  smooth,  with  fine  lines  of  growth ;  other  features,  as  far  as 
known,  the  same  as  in  G.?  pealei. 

Length  of  an  average  specimen,  13  mm.;  breadth  of  body  whorl, 
7.5  mm. 

Nearly  all  the  specimens  are  in  the  form  of  imperfect  internal  casts 
retaining  portions  of  the  shell,  but  of  course  not  showing  the  generic 
features  fully.     It  seems  to  be  related  to  G^.?  pealei. 

The  type  is  from  the  same  horizon  as  the  preceding  on  Fawn  Creek, 
and  it  occm-s  in  this  bed  at  several  localities  in  that  resrion. 

Amnicola?  ceetacea  n.  sp. 
PI.  LXXV,  fig.  8.     • 

Shell  small,  conical,  consisting  of  four  or  five  rapidly  increasing  con- 
vex whorls;  suture  deeply  impressed;  surface  marked  only  by  lines  of 
gi-owth;  aperture  oval. 

Height,  9  mm.;  breadth  of  last  whorl,  6  mm. 

Occui's  with  the  preceding  species  on  Fawn  Creek. 

COLORADO  FORMATION. 
PELECYPODA. 

OsTREA  ANOMioiDEs  Meek. 

Ostrea  anomioides  Meek,  1873 :  Ann.  Kept.  TJ.  S.  Geol.  Surv.  Terr,  for  1872,  p.  488. 
White,  1S80:  Idem  for  1878,  p.  10,  PI.  XI,  figs.  4«,  6.  1884:  Fourth  Aim.  Kept. 
U.  S.  Geol.  Surv.,  p.  291,  PI.  XXXIX,  figs.  4  aud  5,  Stanton,  1894:  Bull.  U.  S. 
Geol.  Surv.  No.  106,  p.  55,  PI.  I,  figs.  5  and  6. 

This  species,  which  was  originally  described  from  the  Missouri  River 
below  Gallatin,  Montana,  is  abundant  in  sandy  shales  near  the  base  of 


634  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

the  Colorado  formation  on  ridg-e  north  of  north  head  of  Gardiner  and  on 
north  side  of  Fan  Creek. 

Inoceramus  umbonatus  Meek  and  Hayden. 

Inoceramus  umbonaius 'Meeli.  and  Hayden,  1858:  Proc.  Acad.  Nat.  Sci.  Pliila.,  p.  50. 
Meek,  1876:  U.  S.  Geol.  Surv.  Terr.,  Vol.  IX,  p.  44,  PI.  Ill,  figs,  la,  b,  c;  PI. 
IV,  figs.  1«,  b  and  2«,  h.  Stanton,  1894:  Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  81, 
PL  XVIII,  figs.  1  and  2. 

One  specimen  was  collected  on  north  bank  of  Snake  River  one-fourth 

mile  above  the  mouth  of  Sickle  Creek.     The  species  is  abundant  in  the 

shales  of  the  upper  part  of  the  Colorado  formation  on  the  Missouri  River 

below  Fort  Benton,  Montana,  and  it  has  recently  been  collected  by  Mr. 

G.  K.  Gilbert  in  the  Niobrara  shales  near  Rocky  Ford  on  the  Arkansas 

River  below  Pueblo,  Colorado.     It  also   occurs  in  the  Austin  limestone 

of  Texas. 

Inoceramus  undabundus  Meek  and  Hayden. 

Inoceramus  undahuiidus  Meek  and  Hayden,  1862:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  26. 
Meek,  1876 :  U.  S.  Geol.  Surv.  Terr.,  Vol.  IX,  p.  60,  PI.  Ill,  figs.  2a,  b.  Stanton, 
1894:  Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  84,  PI.  XVI,  figs.  1  and  2. 

Occurs  Avith  the  preceding  at  the  locality  on  Snake  River,  and  also  on 
the  Missouri  below  Fort  Benton. 

Inoceramus  flaccidus  White. 

Inoceramus  flaccidus  White,  1876:  U.  S.  Geog.  and  Geol.  Surv.  W.  lOOtli  Meridian, 
Vol.  IV,  p.  178,  PI.  XVI,  figs,  la  and  h.  Stanton,  1894:  Bull.  U.  S.  Geol.  Surv. 
No.  106,  p.  80,  PI.  XIII,  fig.  1. 

Occurs  with  the  preceding,  and  at  the  same  horizon,  one-fourth  mile 
farther  up  Snake  River.  It  has  hitherto  been  found  only  in  the  Niobrara 
shales  near  Pueblo,  Colorado. 

Inoceramus  acuteplicatus  n.  sp. 

PI.  LXXV,  figs.  9  and  10,  and  PI.  LXXVI,  fig.  1. 

Shell  large,  moderately  convex,  elongate,  with  the  height  much  greater 
than  the  length;  hinge  line  rather  short,  oblique  to  the  longer  axis  of  the 
shell;  beak  prominent,  acute,  near  the  anterior  end  of  the  hinge  line; 
anterior  side  gently  convex,  posterior  nearly  straight ;  base  broadly  rounded, 
with  a  tendency  to  angulation  at  the  junction  with  the  sides;  surface  marked 


MESOZOIC  FOSSILS.  635 

by  lines  of  growth  and  by  i-egiilar,  naiTOw,  elevated,  concentric  ridges  that 
are  about  one-third  as  wide  as  the  interspaces.  These  ridges  are  somewhat 
stronger  on  the  anterior  half  of  the  shell  than  on  the  posterior,  and  in  very 
large  specimens  they  tend  to  become  obsolete,  making  the  basal  portion  of 
the  shell  nearly  smooth. 

The  above  description  is  drawn  mainly  from  a  large  right  valve 
(PI.  LXXVI,  fig.  1)  from  the  Sickle  Creek  locality.  The  specimens  associ- 
ated with  it  and  having  the  same  general  form  and  sculpture  are  all  much 
smaller.  These  are  not  distinguishable  from  specimens  from  sandstone 
believed  to  belong  to  a  higher  horizon  on  Glade  Creek.  There  are  small 
left  valves  in  the  collection  from  both  localities,  and  one  of  those  from 
Grlade  Creek  is  figured.  It  is  proportionally  more  convex  than  the  right 
valve,  and  the  beak  is  more  prominent  and  more  curved.  The  concentric 
ridges  are  very  prominent  on  the  convex  median  region,  and  fade  out 
toward  the  borders. 

The  largest  type  specimen  measures  201  mm.  in  its  longest  diameter, 
and  135  mm.  at  rifflit  ang-les  to  that  line. 

This  species  is  related  to  I.  fragilis  and  I.  altus,  all  tkree  belonging  to 
the  typical  section  of  Inoceramus.  It  difi"ers  from  both  of  them  in  being 
more  strongly  plicate,  in  its  shorter,  slightly  more  oblique  hinge  line,  and  in 
other  details  of  outline. 

Locality  and  position:  On  Snake  River  one-fourth  mile  above  the 
mouth  of  Sickle  Creek,  associated  with  /.  umhonatus,  Scaphites  ventricosus, 
etc.,  in  sandy  shales  of  the  upper  part  of  the  Colorado  formation,  and  near 
the  mouth  of  Glade  Creek  in  a  sandstone  supposed  to  belong  to  a  higher 
horizon. 

CoRBULA  suBTRiGONALis  Meek  and  Hayden. 

Corbula  subtrigonalis  Meek  and  Hayden,  1856:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  116. 
White,  1880:  Ann.  Eept.  U.  S.  Geol.  Surv.  Terr,  for  1878,  p.  80,  PI.  XXV,  figs. 
6a-/.  White,  1883 :  Third  Ann.  Eept.  U.  S.  Geol.  Surv.,  p.  442,  PI.  XIX,  figs. 
10-13.  Stanton,  1894 :  Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  123,  PL  XXVII,  figs.  7 
and  8. 

This  species  and  its  variety  perundata  were  obtained  in  black  shales 
supposed  to  belong  to  the  Colorado  formation  near  Electric  Peak  and  on 
the  Cone  head  of  Gardiner  River.  These  forms  were  originally  described 
from  the  Laramie,  but  they  are  known  to  range  as  low  as  the  Colorado 
formation  in  southwestern  Wyoming. 


636  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

CEPHALOPODA. 

Baculites  asper  Morton? 

Baculites  asper  Morton,  1834:  Synopsis  Org.  Eem.  Cret.  Gr.,  p.  43,  PI.  I,  figs.  12  and  13; 
PL  XIII,  fig.  2.  Stanton,  1891:  Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  167, 
PI.  XXXVI,  figs.  4  and  5. 

Occurs  with  Inoceranms  aciitepUcatus,  etc.,  at  the  locahty  one-fourth 
mile  above  the  mouth  of  Sickle  Creek,  and  is  abundant  associated  with  the 
same  fauna  on  the  Missouri  River  below  Fort  Benton,  in  the  upper  part  of 
the  Colorado  formation.     It  is  also  found  at  Cinnabar  Mountain. 

ScAPHiTES  VENTRicosus  Meek  and  Hayden. 

Scaphites  ventricosus  Meek  and  Hayden,  1862:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  22. 
Meek,  1876:  U.  S.  Geol.  Surv.  Terr.,  Vol.  IX,  p.  425,  PI.  VI,  figs.  7a,  h,  and  8a,  b. 
Stanton,  1894:  Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  186,  PI.  XLIV,  figs.  8-10; 
PI.  XLV,  fig.  1. 

Several  specimens  from  the  localities  above  mentioned  on  Snake  River, 
and  a  fragment  believed  to  belong  to  this  species  from  the  black  shales  of 
Electric  Peak. 

It  occurs  well  preserved  at  Cinnabar  Mountain  just  north  of  the  Park, 
and  with  the  preceding  species  below  Fort  Benton. 

MONTANA  FORMATION.! 

BRACHIOPODA. 

LiNGULA  suBSPATULATA  Hall  and  Meek. 

Lingula  subspatulata  Hall  and  Meek,  1854:  Mem.  Am.  Acad.  Arts  and  Sci.,  Vol.  V, 
p.  380,  PI.  I,  figs.  2rt,  h.  White,  1876:  U.  S.  Geog.  and  Geol.  Surv.  W.  100th 
Meridian,  Vol.  IV,  p.  169,  PI.  XV,  fig.  4a. 

Two  specimens  from  sandstone  overlying  bituminous  shale  on  Rattle- 
snake Creek,  probably  same  horizon  as  the  remainder  of  the  species 
mentioned  below. 


'  See  pp.  606-607  for  remarks  on  the  horizon  of  the  following  species. 


MKSOZOIO  FOSSILS.  637 

PELECYPODA. 

OsTREA  soLENiscus  Meek. 

Ostrea  soleniscus  Meek,  1871:  Proc.  Am.  Philos.  Soc,  Vol.  XI,  p.  435.  White,  1880: 
Ann.  Kept.  U .  S.  Geol.  Surv.  Terr,  for  1878,  p.  9,  PI.  XI,  figs.  2a,  b.  1884 :  Fourth 
Ann.  Kept.  U.  S.  Geol.  Surv.,  p.  300,  PI.  XLII,  fig.  1.  Stanton,  1894:  Bull.  U.  S. 
Geol.  Surv.  No.  lOG,  p.  56,  PI.  II,  fig.  1;  PL  III,  figs.  1  and  2. 

This  species  is  abundant  in  both  the  Colorado  and  Montana  formations 
at  Coalville,  Utah,  and  in  southwestern  Wyoming.  It  was  obtained  near 
the  second  crossing  of  Snake  River,  just  south  of  the  Park. 

Ostrea  sp.. 

A  small  species  related  to  0.  peUucida  M.  and  H.  occurs  at  the  same 

locality  with  the  preceding. 

Anomia  sp. 

A  small  species  resembling  A.  i)ropatoris  White  is  represented  by 
several  casts  from  Glade  Creek,  Lizard  Creek,  and  near  second  crossing  of 
Snake  River. 

Avicula  nebrascana  Evans  and  Shumard. 

A  vicula  nebrascana  Evans  and  Shumard,  1857 :  Trans.  Acad.  Sci.  St.  Louis,  Vol.  I,  jj.  38. 
Pteria  {Oxytoma)  nebrascana  [E.  and  S.)  Meek,  1870:  Eept.  U.  S.  Geol.  Surv.  Terr., 

Vol.  IX,  p.  34,  PI.  XVI,  fig.  3fl,  b;  PI.  XXVIII,  fig.  11.     Whitfield,  1880:  Geol. 

Black  Hills  Dakota,  p.  385,  PI.  VII,  fig.  4. 

Several  specimens  from  the  locality  near  the  mouth  of  Grlade  Creek. 
It  is  a  widely  distributed  species  in  the  Fort  Pierre  shales  of  the  Montana 
formation. 

Avicula  lingu^formis  Evans  and  Shumard. 

Avicula  linguceformis  Evans  and  Shumard,  1854:  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  153. 
Pteria  Zm^M»/brwm  (E.  and  S.)  Meek,  1876:  Eept.  U.  S.  Geol.  Surv.  Terr.,  Vol.  IX, 

p.  32,  PI.  XVI,  figs.  l(t-d.     Whitfield,  1880 :  Geol.  Black  Hills  Dakota,  p.  384, 

PI.  VII,  figs.  2  and  3. 

This  species  occurs  with  the  preceding  on  Grlade  Creek  and  has  about 
the  same  geographic  and  vertical  range. 

Inoceramus  acuteplicatus  n.  sp. 

Numerous  small  specimens  referred  to  this  species  from  locality  near 
the  mouth  of  Glade  Creek.     (See  description  on  page  634.) 


638  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Aeca  sp. 

A  single  imperfect  specimen,  probably  of  an  undescribed  species,  from 
the  locality  near  the  second  crossing  of  Snake  River. 

NucuLA  sp. 

A  cast  near  mouth  of  Glade  Creek. 

Cardium  paupeeculum  Meek. 

Cardium  pmiperculum  Meek,  1871:  Ann.  Rept.  U.  S.  Geol.  Surv.  Terr,  for  1870,  p.  306. 

White,  1879:  Idem  for  1877,  p.  291,  PI.  IX,  fig.  3a.     Stanton,  1894:  Bull.  U.  S. 
Geol.  Surv.  No.  106,  p.  99,  PI.  XXII,  figs.  9-12. 
Cardium  subcurtum  Meek,  1873:  Ann.  Rept.  U.  S.  Geol.  Surv.  Terr,  for  1872,  p.  476. 
1877 :  U.  S.  Geol.  Expl.  40th  Parallel,  Vol.  IV,  Pt.  I,  p.  152,  PI.  XV,  fig.  3a. 

This  is  the  most  abmidant  species  in  the  sandstones  near  Glade  Creek, 
near  second  crossing  of  Snake  River,  and  on  Lizard  Creek. 

It  is  common  in  the  Colorado  formation  at  Coalville,  Utah;  in  south- 
western Wyoming,  and  in  Huerfano  Park,  southern  Colorado.  In  these 
localities  it  is  not  known  to  range  as  high  as  the  Montana  formation. 

Baroda  wyomingensis  Meek. 

Tapes  wyomingensis  Meek,  1871 :  Ann.  Rept.  U.  S.  Geol.  Surv.  Terr,  for  1870,  p.  310. 
Baroda  wyomingensis  Meek,  1873:  Idem  for  1872,  p.  493.     White,  1879:  Idem  for  1877, 
p.  293,  PI.  X,  figs.  3a,  h. 

A  single  specimen  from  Glade  Creek. 

It  is  possible  that  this  species  belongs  to  Conrad's  genus  Legumen, 
described  from  the  Cretaceous  of  Ripley,  Mississippi.  I  have  elsewhere* 
expressed  the  opinion  that  Baroda  is  probably  a  synonym  of  Legumen, 
which  is  a  prior  name. 

DoNAX  cuneata  Stanton. 

DoNAx(?)  OBLONGA  Stauton. 
Both  these  species  occur  on  a  single  hand  specimen  from  near  the 
second  crossing  of  the  Snake  River.  The  type  of  D.  cuneata  was  collected 
in  sandstone  of  the  Colorado  formation  at  Old  Bear  River  City,  southwestern 
Wyoming,^  and  D.  oblonga  came  from  the  same  hoi'izon  at  Coalville,  Utah. 
D.  cuneata  occurs  also  in  the  Montana  formation  of  the  Coalville  section. 


'Bull.  U.  S.  Geol.  Surv.  No.  106,  p.  107.  ^i^em,  p.  110,  PI.  XXV,  fig.  1. 


MESOZOIC  FOSSILS.  639 

Mactra  warrenana  Meek  and  Hayden. 

Mactra  warrenana  Meek  and  Hayden,  185G :  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  271. 
Mactra  (Gymhophoraf)  warrenam  (M.  and  H.)  Meek,  187C:  Eept.  U.  S.  Geol.  Surv. 
Terr.,  Vol.  IX,  p.  208,  PI.  XXX,  figs.  7a-<?. 

Casts  ill  sandstone  apparently  belonging  to  this  species  are  abundant 
near  Glade  Creek.  The  species  is  widely  distributed  in  the  Montana 
formation. 

Mactra  arenaria  Meek? 

Mactra  {Trigonella?)  arenaria  Meek,  1877:  U.  S.  Geol.  Expl.  40tb  Parallel,  Vol.  IV, 
Pt.  I,  p.  154,  PI.  XIV,  fig.  5. 

This  species  is  abundant  in  the  Montana  formation  at  Coalville,  Utah. 
A  single  cast  that  seems  to  belong  to  it  is  associated  with  the  preceding 
species  near  Glade  Creek. 

GASTROPODA. 

Gyrodes  depressa  Meek. 

Gijrodes  depressa  Meek,  1877 :  U.  S.  Geol.  Expl.  40tb  Parallel,  Vol.  IV,  Pt.  I,  p.  159, 
PI.  XV,  figs.  1,  la.  Stanton,  1894:  Bull.  U.  S.  Geol.  Surv.  No.  lOG,  p.  135, 
PI.  XXIX,  figs.  11-14. 

Common  in  the  sandstones  on  Glade  Creek.  It  was  originally 
described  from  the  Colorado  formation  at  Coalville,  Utah,  and  is  found  at 
the  same  horizon  in  Huerfano  Park,  Colorado.  The  genus  Gyrodes  has 
not  hitherto  been  reported  from  the  Montana  formation  of  the  Rocky 
Mountain  region,  but  it  is  well  represented  in  beds  of  the  same  age  in  the 
Atlantic  and  Gulf  border  region.  In  fact,  Gyrodes  petrosa  (Morton)  from 
the  Ripley  formation  is  scarcely  distinguishable  from  G.  depressa. 

Cerithium?  sp. 

A  small,  slender  form  of  doubtful  atfinities,  represented  by  an  internal 
cast  from  sandstone  on  Huckleberry  Mountain. 

Pyrula?  sp. 
A  fragmentary  cast  from  Glade  Creek. 


640     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

CEPHALOPODA. 

ScAPHiTES  cf.  vENTRicosus  Meek  find  Hayden. 

A  mere  fragment  from  Glade  Creek,  resembling  this  species  in  sculp- 
tm-e.     (See  p.  636.) 

Placenticekas  placenta  (DeKay)f 

Ammonites  placenta  DeKay,  1S37:  Ann.  New  York  Lyceum  Nat.  Hist.,  Vol.  II,  p.  278, 

PI.  V,  fig.  3. 
Placenticeras  placenta  (DeKdiy)  ]Meek,  1876:  Eept.  U.  S.  Geol.  Surv.  Terr.,  Vol.  IX, 

p.  465,  PI.  XXIV,  figs.  2«,  b. 

A  fragment  probably  belonging  to  this  well-known  species  was 
collected  near  the  second  crossing  of  the  Snake  River.  The  species  ig 
abundant  and  widely  distributed  in  the  Montana  formation  and  its  equiva- 
lents, and  a  few  specimens  of  it,  or  of  a  verj^  closely  related  species,  have 
been  obtained  in  the  Colorado  formation. 


PLATE   LXXII. 


641 
MON  XXXII,  PT  II il 


PLATE    L  X  X  I I  . 

Page. 
L'hyuclioinlJa  (inalhophura  Meeki; 609 

Figs.    1,  2.  Two  views  of  a  small  specimen  from  near  Snalce  River;  enlarged  li  diameters. 

3,  4.  Similar  views  of  a  larger  example  from  near  Vermiliou  Canyon,  northwestern 
Colorado;  enlarged  U  diameters  (United  States  National  Museum,  No  88.53;. 

(Injphcfa  cttlceoln  var.  iichrasueiisia  M.  and  H 612 

Fig.     .5.  Small  left  valve  with  strong  stria' ;  enlarged  li  diameters. 
6.7.  Two  views  of  a  larger  specimen;  niitural  size. 

JAtiitt  rinmihaveitsis  u.  sp 612 

Fk;.      S.  Right  valve;  enlarged  li diai'jeters. 

Gryphaa  plaiioconvexa  Whittield 611 

Fig.     9.  Left  valve  from  near  lower  canyon  of  the  Yellowstone  (United  States  National 
Museum,  No.  12309). 
10.  Right  valve  from  near  Snake  River. 

Camptoneetes pertenmslviatus  H.  and  W 614 

Fig.    11.  Right  valve  from  Flat  Moniit.iiM,  slightly  distorted.     The  obscure  radiating  ridges 
are  probably  ac<idental. 

Cumptonectea  beUisiriatiis  Meek 613 

Fig.    12.  Right  valve  from  the   Bighorn   Mountains,  Wyoming  (United   States   National 
Mnsenm,  No.  188.5). 

Camptoneetes  heUlstriatiiK  var.  dixtaiis  n.  var 614 

Fig.    13.  Right  v.ilve. 

642 


U.  9.  QEOUXUCAL  SURVtV 


MONOGRAPH  XXXII      PART  II      PL.    L  XXII 


JURASSIC.     ELLIS   FORMATION. 


PLATE   LXXIII. 


643 


PLATE    L  XXIII. 

CiiculUca  haijuei  Meek 618 

Fir;.      1.  Left  valve  slightly  Hattened  and  showing  buth  surface  sculiiture  and  liinge  impres- 
sion; enlarged  2  diameters. 

TrUjonia  eleganlisshna  Meek 619 

Fig.      2.  Left  valve;  enlarged  1+ diameters. 

Astarte  meeki  n.  sp 620 

Fig.      3.  Right  valve  from  Cinnabar  Mountain  ;  enlarged  li  diameters. 

4.  Left  valve  from  lower  canyon  of  Yellowstone;  enlarged  U  diametws  (United  States 

National  Mnsenm,  No.  12374). 

5.  Elongate  right  valve,  probably  distorted  by  pressure,  and  showing  impression  of 

the  erenulate  interior  margin;  enlarged  2  diameters. 
Tancredia  i  kiiowltoiii  u.  sp 621 

Fin.      6.  Cast  of  right  valve;  enlarged  14  diameters. 
Cyprina  ?  cinnahurensis  n.  sp 621 

Figs.    7,  8.  Two  views  of  an  internal  cast,  one  of  the  types. 
Cypiina  ?  iddhujsl  n.  sp 622 

Fig.     9.  Eight  valve  of  the  type. 
Til lacia  f  montanaensis  (Meek) ? 628 

Fig.    10.  Right  valve,  supposed  to  be  Meek's  original  type;  enlarged  lA  diameters. 
Vjipricardia  f  haguei  n.  sp 623 

Figs.  11,  12.  Two  views  of  an  average  specimen,  internal  cast, 
13.  Right  valve  of  a  large  elongate  specimen. 

644 


U.  6.  OEOaXUCAL  :»uRvev 


MONOGRAPH  XXXII      PART  II      PL.  LXXI1I 


JURASSIC       ELLIS    FORMATION 


PLATE   LXXIV. 


645 


PLATE    LXXIV. 

Paga 
}'hi)laduiiii/a  khxji  Meek _ 624 

Fii;s.  1,  2.  Two  views  of  Meek's  type  (United  States  National  Museum,  No.  7815). 
3.  Left  valve  of  unusually  smooth  foriii. 
Pholadomija  imnjiiiplicaia  u.  sp    625 

Fk;.   4.  Right  valve  of  the  type. 
Anatiixi  punctata  n.  sp 628 

Fl(i.  5.  Left  valve  of  the  type.     The  sculpture  is  somewhat  restored. 
Homomya  galfatiiiensis  n.  sp 625 

Figs.  6,  7.  Two  views  of  the  type,  an  iuterual  cast. 
rieiiromj/a  siibcomjiressa  Meek 626 

Fios.  8-11.  S)ie(imeu8  showing  variation  ju  outline  and  sculpture  of  forms  assigned  to  this 
.species. 

646 


U.   8.   QEOLOaiCAL  8URVEV 


MONOGRAPH    XXXll      PART  II       PL.    LXXIV 


JURASSIC,      ELLIS    FORMATION. 


PLATE   LXXV. 


647 


PLATE    LXXV. 

JURASSIC   SPECIES. 

Page. 

Th  racia  weed)  n.  sp 627 

Fig.   1.  Kiglit  valve  of  usual  size  autl  outline. 

2.  Left  valve  of  a  shorter  forui. 

3.  Left  valve  of  an  elongate  specimen. 

Keritina  wyomingensls  u.sp 629 

Figs,  i,  5.  Opposite  views  of  tbe  type ;  enlarged  3  diameters. 

CRETACEOUS   SPECIES. 

Goniobasis'i  2><^<ilei  n.  sp 632 

Fig.  6.  An  average  specimen ;  enlarged  2  diameters. 
Goniobasis'i  increhesceiis  n.  sp 633 

Fig.   7.  A  medium-sized  specimen;  enlarged 2  diameters. 
Amiiicola^  cretaeea  u.  sp 633 

Fig.   8.  An  average  specimen ;  enlarged  2  diameters. 
Inoceramus  acuteplicatus  u.  sp 634 

Fig.  9.  A  small  left  valve  supposed  to  belong  to  this  species. 

10.  A  small  right  valve.     (See  PL  LXXVI  for  additional  figure.) 

648 


U.   6.   OEOLOOICAL  SUh/EV 


MONOGHAPH  XXXII      PAHT  II      PL-   IXXV 


JURASSIC   AND   CRETACEOUS      ELLIS,    DAKOTA,    AND    MONTANA    FORMATIONS 


PLATE   LXXVI. 


64fl 


PLATE    LXXVI. 

Page. 

Itioceramiit  aciitepUcatiis  n.  sp - 634 

Fk;.   1.  A  large  right  valve,  fnrmiuy  the  principal  type  specimeu.    (See  Fl.  LXXV  lor  addi- 
tional tigures.) 

650 


U.  S.  OEOLOOICAL  SURvCV 


MONOGRAPH  XXXII      PART  II      PL.    LXXVI 


CRETACEOUS      COLORADO   FORMATION. 


CHAPTER    XIV. 
FOSSIL  FLORA    OF   THF    YELLOWSTONE    NATIONAL   PARK. 


By  Frank  Hall  Knowlton. 


HISTORICAI.  SUMMARY  OF  WORK  OX  THE  FOSSIL  FLORA. 

As  nearly  as  I  have  been  able  to  determine,  the  tirst  collectiou  of  fossil 
plants  made  in  the  Yellowstone  National  Park  was  obtained  by  members 
of  the  United  States  Geological  Survey  under  Dr.  F.  V.  Hayden,  in  187L 
They  were  found  in  two  localities,  and  were  recorded  by  Prof.  Leo  Les- 
quereux,^  as  follows:  "Divide  between  the  source  of  Snake  River  and  the 
southern  shore  of  Yellowstone  Lake,"  and  "  Near  Yellowstone  Lake,  among 
basaltic  rocks."  It  has  not  been  possible  to  rediscover  these  localities,  and 
several  of  the  species  remain  unique. 

In  the  following  year  (1872)  the  Park  was  again  visited  by  a  party 
under  Dr.  Hayden.  The  members  of  this  party  investigated  the  north- 
eastern portion  of  the  Park  and  discovered  the  rich  plant  deposits  on  the 
Yellowstone  River,  a  short  distance  below  the  mouth  of  J]lk  Creek.  The 
actual  collectors  were  Messrs.  A.  C.  Peale,  Joseph  Savage,  and  0.  C.  Sloane. 
The  plants  represented  five  species,  which  were  determined  by  Professor 
Lesquereux.- 

The  Fossil  Forest,  that  has  since  become  so  widely  known,  was  first 
described  by  Mr.  W.  H.  Holmes  in  1878.*  He  visited  and  quite  thoroughly 
explored  the  Fossil  Forest  and  vicinity  and  made  a  small  collection  of 
plants  that  were  submitted  to  Professor  Lesquereux.  Most  of  these  plants 
were  determined  to  be  new  to  science,  but  they  were  neither  named  nor 

'  Ann.  Rept.  U.  S.  Geol.  and  Geog.  Surv.  Terr,  for  1871,  pp.  295,  299. 

=  0p.  cit.,  Rept.  lor  1872,  p.  403. 

'  Op.  cit.,  Rept.  lor  1878,  Ft.  11.  pp.  47-50. 

651 


(352  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

described.  Holmes  pointed  out  the  fact,  since  abundant!}'  confirmed,  of 
the  succession  of  forests  that  have  been  entombed  one  above  another.  His 
section  of  Amethj-st  Mountain  shows  clearly  this  remarkable  phenomenon. 

In  October,  1874,  Dr.  Otto  Kuntze,  a  celebrated  German  botanist,  then 
on  a  botanical  exploring  journey  around  the  world,  visited  the  Park  and 
made  some  interesting  observations  on  the  process  of  petrifaction  of  trees 
now  going  on  in  the  vicinity  of  the  geysers  and  hot  springs.  His  paper 
was  not  printed,  however,  until  his  return  to  Germany  in  1880.^ 

Tlie  thorough  exploitation  of  the  Park  was  begun  and  carried  on  for 
several  years  by  the  Yellowstone  Park  Division  of  the  present  Geological 
Survey.  In  1883  the  work  was  extended  toward  the  northeastern  portion 
of  the  Park,  and  collections  of  greater  or  less  extent  were  made  at  many 
places.  In  1885  the  Fossil  Forest  section  was  worked  out,  and  large  col- 
lections were  made  by  Mr.  Arnold  Hague,  Mr.  W.  H.  Weed,  Mr.  George  M. 
Wright,  and  Prof  J.  P.  Iddings. 

In  the  summer  of  1887,  Prof.  Lester  F.  Ward  and  I  spent  about  six 
weeks  in  the  vicinity  of  the  Fossil  Forest,  making  large  collections  of  fossil 
wood  and  leaf  impressions.     The  exact  localities  are  enumerated  below. 

The  following  season  I  spent  two  months  in  the  same  area,  discovering 
many  new  beds  of  plants  and  more  thoroughly  exploring  and  collecting 
from  l)eds  ]n-eviously  known.  These  are  also  recorded  in  the  following  list 
of  localities. 

LIST    OF    LOCALITIES   AT  WHICH    FOSSIL   PLANTS    HAVE  BEEN  COLLECTED   IN 
THE   YELLOWSTONE    NATIONAL    PARK. 

1871. 

Divide  between  tlie  source  of  Snake  River  aud  the  southern  shore  of  Yellowstone 
Lake;  Hayden  survey.     (Not  since  observed.) 

Near  Yellowstone  Lake,  aiuoug  basaltic  rocks;  Hayden  survey.  (Not  since 
found.) 

1872. 

Yellowstone  River  below  mouth  of  Elk  Creek;  A.  C.  Peale,  Joseph  Savage, 

and  O.  G.  Sloaue. 

1878. 

Amethyst  Mountain  in  vicinity  of  Fossil  Forest;  W.  H.  Holmes. 


'  Das  AiisUmd,  1880,  pp.  361-364,  390-393,  669-672,  684-689. 


FOSSIL  FLORA.  653 


1883. 

Aiulesitic  breccia  near  {•ulch  northwest  of  peak  west  of  Dunraven ;  J.  P.  Iddiiigs, 
September  12,  1883.     (Field  Nos,  SG,  77.) 

Needle  Hill  near  Yanceys;  W.  H.  Weed,  October  9,  1883. 

TQwer  Creek;  Arnold  Hague,  September  16,  1883,     (Field  Nos.  1030,  1031.) 

1884. 

Fossil    Forest  section,   lower  stratum;  Arnold    Has'ue,    September  24,   188-t. 

(No.  1221.)  , 

Fossil  Forest  section,  middle  stratum;  Arnold  Hague,  September  24,  1884. 
(No.  1220.) 

Fossil  Forest  section,  ujjper  stratum;  Arnold  Hague,  September  24,  1884. 
(Nos.  1217,  1218,  1219.) 

Sandstone  on  top  of  ridge  west  of  Mink  Creek;  Arnold  Hague.     (No.  2332.) 

1885. 

Signal  Hill;  W.  H.  Weed,  September  28, 188.J. 

Head  of  Tower  Creek;  W.  H.  Weed,  September  25, 1885. 

East  slope  of  high  hill  three-fourths  mile  south  from  "Yanceys ;  George  M.  Wright, 
September  4,  1885. 

Near  top  of  south  wall  of  canyon  of  Yellowstone  Eiver,  about  1  mile  up  stream 
from  mouth  of  Hellroaring  Creek;  George  M.  Wright,  September  9,  1885. 

Fossil  Forest  section,  No.  1  of  section ;  W.  H.  Weed  and  George  M.  Wright, 
September  19,  1885. 

Fossil  Forest  section.  No.  15rt  of  section;  "\V.  H.  Weed  and  George  M.  Wright, 
September  19,  1885. 

Fossil  Forest  section.  No.  22c  of  section;  W.  H.  Weed  and  George  M.  Wright, 
September  20, 1885. 

Fossil  Forest  section,  No.  20  of  .section;  W.  H.  Weed  and  George  M.  Wright, 
September  20,  1885. 

Fossil  Forest  section.  No.  20  of  section ;  W.  H.  Weed  and  George  M.  Wright, 
September  20, 1885. 

Top  of  Mount  Everts,  west  face,  nearly  opposite  bridge  over  Gardiner  Eiver, 
between  Mammoth  Hot  Springs  and  Gardiner;  George  M.  Wright,  July  7,  1885.      , 

1887. 

Fossil  Forest,  bed  No.  1,  lowest  bed  about  7,700  feet  altitude;  Lester  F.  Ward 
and  F.  H.  Knowlton,  August,  1887. 

Fossil  Forest,  bed  No.  2;  Lester  F.  Ward  and  F.  H.  Knowlton,  August,  1887. 

Fossil  Forest,  bed  No.  3,  "Magnolia  bed,"  300  feet  above  bed  No.  1;  Lester  F. 
Ward  and  F.  H.  Knowlton,  August,  1887. 

Fossil  Forest,  bed  No.  4,  "  Aralia  bed,"'  425  feet  above  bed  No.  1 ;  Lester  P, 
Ward  and  F.  H.  Knowlton,  August  20,  1887. 


654  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAliK. 

Fossil  Forest,  bed  No.  5,  "  Salix  bed,"  about  400  feet  above  bed  No.  1 ;  Lester  F. 
Ward  and  F.  H.  Knowltou,  August  19,  1887. 

Fossil  Forest,  bed  No.  6,  "  Platanus  bed,"  425  feet  above  bed  No.  1 ;  Lester  F. 
Ward  aiul  F.  H.  Kuowltoii,  August  19,  1887. 

Fossil  Forest,  bed  No.  7,  highest  bed.  515  feet  above  bed  No.  1;  Lester  F.  Ward 
aud  F.  H.  Kuowlton,  August,  1887. 

Hill  back  of  Yaueeys,  near  standing  trunks;  Lester  F.  Ward  and  F.  H.  Kuowl- 
toii, Augn.st  10,  1887. 

Cliff  west  of  Fossil  Forest  Ridge,  near  Chaleedouy  Greek,  lowest  bed,  altitude 
about  7,900  feet;  Lester  F.  Ward  aud  F.  H.  Knowlton,  August  15,  1887. 

Cliff  west  of  Fossil  Forest  Ridge,  upper  bed,  250  feet  above  lower  bed;  Lester 
F.  Ward  and  F.  H.  Knowlton,  August  15,  1887. 

East  end  of  Fossil  Forest  Mountain,  bed  on  same  horizon  as  fossil  trunks; 
Lester  F.  Ward  aud  F.  11.  Knowlton,  August  13  and  22,  1887. 

Specimen  IMdge,  head  of  Crystal  Creek,  opposite  mouth  of  Slough  Creek, 
"Platanus  bed,"  altitude  about  7.500  feet;  Lester  F.  Ward  aud  F.  H.  Knowlton, 
August  24,  1887. 

Si)ecimen  Eidge,  opposite  mouth  of  Slough  Creek,  "Quercus  bed,"  100  feet  above 
"Platanus  bed;"'  Lester  F.  Ward  aud  F.  H.  Knowlton,  August  25,  1887. 

North  of  Pinyon  Peak,  on  Wolverine  Creek,  altitude  7,900  feet;  Arnold  Hague, 
August  10,  1887. 

1888. 

Yellowstone  River,  ouehalf  mile  below  mouth  of  Elk  Creek,  bottom  of  bluff"; 
F.  H.  Knowlton,  August  29,  1888. 

Yellowstone  River,  one  half  mile  below  mouth  of  Elk  Creek,  30  or  40  feet  above 
the  river;  F.  H.  Knowlton,  August  27,  1888. 

Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek,  lop  of  bluff';  F.  H. 
Knowlton,  August  27,  1888. 

Bluff"  on  Yellowstone  River,  1  mile  below  mouth  of  Elk  Creek:  F.  H.  Knowlton, 
August  4,  1888. 

Cliff"  on  Yellowstone  River,  short  distance  above  mouth  of  Hellroaring  Creek; 
F.  H.  Knowlton,  August  10,  1888. 

Southeast  side  of  hill  above  Lost  Creek,  bed  No.    I;  F.  H.  Knowlton,  August 

8,  1888. 

Southeast  side  of  hill  above  Lost  Creek,  bed  No.  2;  F.  H.  Knowlton,  August 

8,  1888. 

Southeast  side  of  hill  above  Lost   Creek,  beds  No.  3,  4,  5;  F.   H.  Knowlton, 

August  8,  1888. 

Southern  end  of  Crescent  Mill,  300  feet  above  wagon  road;  F.  H.  Knowlton, 
August  9,  1888. 

Southern  end  of  Crescent  Hill,  "  Platanus  bed":  F.  H.  Knowlton.  Angu.st  9, 1888. 

Northeast  side  of  Crescent  Hill,  oiiposite  small  pond  in  slope,  altitude  about 
7,500  feet;  F.  IL  Knowlton  and  (I.E.  Culver,  August  2, 1888. 


FosaiL  floi;a.  655 

The  TLmulercr,  opposite  Soda  Butte;  F.  il.  KiiDwIton  and  C.  K.  Culver,  August 
21),  ISSS. 

East  bank  of  Lauiar  Kivi-r,  between  (Jaclie  and  Calfee  creeks;  F.  H.  Kuowltou 
antl  (1.  K.  Culver,  August  21,  1888. 

Ilill  on  road  Just  above  Yaneeys;  F.  II.  Knowlton,  August  G,  1888. 

Hill  near  the  Yancey  fossil  truulcs;  F.  il.  Kuowlton,  August  28, 1888. 

Mount  Everts,  near  summit  of  west  end ;  F.  H.  Kuowltou,  July  27, 1888. 

Mount  Inverts,  coal  opening  ou  side  facing  the  Gardiner  River  (fragments) ;  F.  H. 
Knowlton.  .July  20, 1S8S. 

DESCRIPTION  OF  KXOWN  FOSSIL  PLANTS  FROM  THE  LARAMIE 
OF  THE  YELLOWSTONE  NATIONAL  PARK. 

ASPLENIUM    HAGUEI    11.  S}). 
PI.  LXXVII,  iigs.  1,  2. 

Froiid  thill,  delicate,  lanceolate  in  outline,  bipimiate,  slender,  straight; 
pinupe  alternate,  scattered,  oblono--lanceolate  in  shape,  cut  into  fe\v  coarse 
divisions  which  are  either  entire  or  ag-ain  cut  into  few  obtuse  teeth;  nerva- 
tion obscure,  consisting  of  a  delicate  midvein  and  few  forked  branches 
from  it. 

This  delicate  little  form  is  represented  by  a  dozen  or  more  specimens. 
The  longer  fragment  (tig.  2)  is  about  4.5  cm.  in  length  and  about  l..'i  cm. 
broad.     The  others  are  more  fragmentary. 

Nothing  like  this  has  been  before  reported  from  the  Laramie  group.  It 
has  some  resemblance  to  Sphenoptcris  gui/otfii  Lx.,^  from  the  Green  Kiver 
group  at  Florissant,  Colorado,  but  is  much  smaller  and  of  decidedly  differ- 
ent shape. 

It  is  not  certain  that  it  belongs  to  the  genus  Asplenium,  as  no  fruit  has 
been  observed,  but  it  resembles,  at  least  generically,  a  number  of  forms 
so  referred  from  the  Cretaceous  of  Greanland.  For  the  present  it  may  be 
retained  in  this  genus. 

I  have  named  it  in  honor  of  the  collector,  Mr.  Arnold  Hague,  of  the 
United  States  Geological  Survey. 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek,  Yellowstone 
National  Park;  collected  by  Arnold  Hague,  August  10,  1887. 


1  Ciet.  and  Tc-rt.  FL,  p.  137.  PI.  XXI,  figs.  1-7, 1883. 


656  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

OnOCLKA.   minima   11.  sp 
PI.  LXXVII,  figs.  11-15. 

Fertile  frond  unknown;  >>terile  frond  small,  apparently  deltoid  in 
outline,  deeply  pinnatifid  into  short,  rounded,  obtuse  pinnre,  which  are 
perfectly  entire  or  are  cut  into  few  large,  coarse  teeth;  nervation  as  in  the 
living  0.  sensihllls. 

This  fine  little  species  is  represented  by  a  dozen  or  more  specimens, 
the  best  of  which  are  figured.  They  are  all  apparently-  fragments,  and 
consequently  it  is  impossible  to  make  out  the  real  shape  of  the  frond  with 
any  certainty.  One  of  the  most  perfect  specimens  (fig.  13)  is  about  3.5 
cm.  long,  and  i-epresents  the  upper  portion  of  a  frond  or  possibly  pinnule, 
if  it  is  a  large  compound  frond.  The  larger  fragment  (fig.  15)  is  4.5  cm. 
lono-  and  about  4  cm.  broad,  but  it  is  broken  at  both  ends  and  there  is  no 
means  of  determining  how  long  it  was  originally.  Fig.  12  at  first  sight 
seems  to  be  entirely  diflPerent  from  the  others,  but  on  comparing  it  with  fig. 
14  the  only  dift'erence  observable  is  that  one  is  cut  into  a  few  coarse  teeth 
and  the  other  is  entire.  The  nervation  seems  to  be  the  same  in  all  and  to 
be  identical  with  that  of  the  living  sensitive  fern. 

Regarding  this  interesting  species,  I  am  somewhat  uncertain  as  to  the 
shape  of  the  frond,  and  less  so  as  to  the  genus  to  which  it  belongs.  Two  of 
the  inost  perfect  forms  (figs.  11,  13)  seem  to  have  come  from  the  upper 
portion  of  a  frond  similar  in  general  shape  to  the  sterile  frond  of  Onodea 
semiUlis;  but,  on  the  other  han<l,  figs.  12  and  14  have  much  the  appear- 
ance of  being  deeply  lobed  pinnte,  resembling  some  of  the  lower  ones  in 
0.  sensibilis.  More  material  will  be  necessary  to  settle  this  ])oint,  iDut  in 
the  meantime  the  species  is  characteristic  enough  to  be  readily  distinguish- 
able, and  hence  is  available  for  geological  purposes. 

This  species  was  at  fii-st  thought  to  be  identical  with  a  plant  that  has 
been  described  under  the  MS.  name  of  Woodtvardia  creinda,  which  comes 
from  Point  of  Rocks,  Wyoming.  This  latter  is  known  <inly  from  a  mere 
fracrment,  however,  and  if  additional  material  could  be  obtained  it  might 
show  them  to  be  the  same.  At  present  TF.  cycnafa  may  be  distinguished  as 
being  much  larger  and  in  having  undulate-crenate  margins  which  are 
minutely  serrate.     The  nervation  is  practically  the  same  in  both. 

Onodea  minima  has  some  resemblance  to  0.  sensibilis  fossilis  from  the 
Fort  Union  group,  near  the  mouth  of  tlie  Yellowstone.     It  differs  in  being 


FOSSIL  FLORA.  057 

liarilly  (ino-fittli  tlio  size  and  in  liaving-  the  lobes  obtuse  and  coarsely  toothed 
instead  ot"  acute  and  entire.     The  nervation  is  nearly  the  same  in  both. 

The  species  under  consideration  has  also  the  same  nervation  as  Wood- 
icardia  preaicolata  tW)m  Crescent  Hill,  but  differs  essentially  in  size  and 
shape. 

The  resendjlance  to  Woodwardia  latUoba  Lx.,  from  the  Denver  group  of 
Colorado,  is  still  more  remote. 

Habitat;  North  of  Piny  on  Peak,  on  Wolverine  Creek,  Yellowstone 
National  Park;  collected  by  Arnold  Hague,  August  10,  1887.  (Field  No. 
3031.) 

Anemia  subcretace.\  (Sap.)  Card,  and  Ett. 

Anemia  subcretacea  (Sap.)  Gard.  aud  Ett.:  Moiiogr.  Brit.  Eoc.  Fl.,  Vol.  I,  Pt.  II,  p. -15, 

PI.  YIII;  PI.  IX,  1880. 
Gymnogramma  luiydeuii  L.:  Ann.  Eept.  U.  S.  GeoL  aud  Geog.  Surv.  Terr.,  p.  295, 1871 

(1872);  Tert.  FL,  p.  59,  PI.  V,  figs.  1-3,1878. 

The  type  locality  of  this  species  is  described  as  "Divide  between  the 
source  of  Snake  River  and  the  southern  shore  of  Yellowstone  Lake."  It 
has  not  since  been  found  inside  the  Park. 

Habitat:  As  above  given. 

Sequoia  langsdorfii?  (Brgt.)  Heer.  ' 
PL  LXXVII,  fig.  5. 

It  is  with  some  hesitation  that  I  refer  this  fragment  to  this  species.  It 
is  small  and  not  well  preserved,  but  the  leaves  appear  to  be  decurrent  and 
to  approach  closer  in  character  to  this  species  than  to  any  other  with  which 
I  am  familiar. 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek,  Yellowstone 
National  Park;  collected  by  Arnold  Hague,  August  10,  1887. 

Sequoia  reichenbachi  (Gein.)  Heer. 

Sequoia  reichenbachi  (Gein.)  Heer:  Flor.  Foss.  Arct.,  YoL  I,  p.  83,  PI.  XLIII,  figs.  Id, 

2b,  5rt,  1808. 
Abietites  dubins  Lx.  ex  p.  Lesquereux:   Tert.   FL,  p.  81,  PI.  VI,  figs.  20,  21,  21a, 

Kuowltou :  BulL  U.  S.  GeoL  Surv.  No.  105,  p.  46,  1893. 

Two  small  worn  fragments  are  refeiTed  to  this  species.  They  are 
obscure,  but  with  little  doubt  are  correctly  referred  to  this  form. 

Habitat:  Mount  Everts;  about  100  feet  above  coal  mine  on  west  end, 
below  Mammoth  Hot  Springs;  collected  by  F.  H.  Knowlton,  July  26,  1888. 

MON  XXXII,  PT  II 42 


658  GEOLOGY  OF  THE  YELLOVVSTO^■E  NATIONAL  PARK. 

Phragmites  falcata  n.  sp. 
PI.  LXXVIII,  fig.  5. 

Leaves  narrowly  lanceolate,  with  a  long  acuminate  apex;  nerves  rather 
sparse,  about  ten  in  the  width  of  the  leaf;  intermediate  nerves  obsolete. 

This  species  rests  upon  the  fragment  figured,  and,  scanty  as  the 
material  is,  dilfers  markedly  from  the  species  with  which  it  is  associated 
and  to  which  it  is  most  closely  related — that  is,  P.  alaskana  Heer. 

The  fragment  is  8  cm.  in  length  and  11  mm.  in  width.  It  tapers  for  a 
distance  of  5  cm.  to  a  long,  sharp  2)oint,  thereby  diftering  from  I\  alaskana, 
which  is  "obtuse  or  obtusely  mucronate."  The  primary  nerves  are  1  mm. 
apart  and  reasonably  distinct.  The  secondary  or  fine  nerves  can  not  be 
made  out,  owing  to  the  poor  state  of  preservation. 

Habitat:  Mount  Everts,  near  summit  of  west  end;  collected  by  F.  H. 
Knowlton,  July  27,  1888. 

Geonomites  schimperi  Lx. 

Geonomites  schimperi  Lx. :  Tert.  FL,  p.  116,  PI.  X,  fig.  1  (1878). 

Sahal  majorl  Ung.     Lesquereux:  Fifth  Auu.  Kept.  U.  S.  Geol.  audGeog.  Surv.  Terr., 
■    p.  295,  1871  (1872). 

This  species  was  collected  with  Anemia  siihcrefacea,  and  the  specimens 
on  which  it  is  based  are  preserved  in  the  United  States  National  Museum. 
The  species  has  not  been  since  collected. 

Habitat:  "  Divide  between  the  source  of  Snake  River  and  the  southern 
shore  of  Yellowstone  Lake." 

Myrica  bolanderi  ?  Lx. 

PI.  LXXVIII,  fig.  4. 

Myrica  bolanderi  Lx. :  Tert.  FL,  p.  133,  PI.  XVII,  fig.  17  (1878). 

Ilex  undulata  Lx. : '  Seventh  Ana.  Kept.  U.  S.  Geol.  and  Geog.  Surv.  Terr.,  1873  (1874), 
p.  416. 

I  refer  this  single  fragment  with  some  hesitation  to  this  species.  It 
differs  slight!)-  frt)m  the  type  specimen,  which  also  appears  to  be  the  only 
one  thus  far  mentioned.     The  one  luider  discussion  is  about  the  same  size 

•  When  this  was  transferred  to  Myrica,  the  specific  name  vndulata  hecame  preoccupied  by  M. 
undulata  (Heer)  Schimp.,  Pal.  V^g.,  Vol.  11,  p.  546  (1870-1872). 


FOSSIL  FLOKA.  659 

ami  has  the  same  toothing  in  tlic  upijcr  jxn-lion,  differing  only  in  being  a 
little  more  acute  than  the  type.     The  Ijasal  jiortion  is  wanting. 

The  loeality  -which  afforded  the  original  specimen  is  unknown  (cf.  Tert. 
Fl.,  p.  133),  but  from  the  fact  that  it  was  sent  to  Les(|uereux  with  a  lot  of 
material  from  near  Florissant,  Colorado,  it  was  assumed  to  belong  to  the 
Green  River  grouj).  It  is  preserved  in  the  collection  of  the  United  States 
National  Museum  (No.  1652),  and  appears  to  have  actuall}'  come  from  the 
Florissant  shale. 

Habitat:  ]\Iount  Everts,  near  summit,  on  western  end;  collected  by 
F.  H.  Knowltou,  July  27,  1888. 

QUKRCUS    ELLISIANA  Lx. 

Pl.LXXVII,ti8.<!. 

Qiierciis  ellisiann  Lx. :  Fifth  Anii.  Kept.  V.  S.  Geol.  and  Geoff.  Surv.  Terr.,  1871  (1872), 
p.  297 ;  Tert.  Fl.,  p.  155,  PI.  XX,  tigs.  4, 5,  7,  8, 1S7.S. 

A  considerable  number  of  specimens  that  leave  no  doubt  as  to  the 
coiTectness  of  their  determination. 

The  example  figured  is  onh'  partially  jjreserved  and  is  much  larger 
than  is  usual  in  this  species.  It  has,  however,  the  shape  and  nervation  of 
Q.  ellisiana,  and  I  refer  it  with  some  hesitation  to  this  form. 

Habitat:  Mount  Everts,  near  the  summit  of  the  Avest  end;  collected 
by  F.  H.  Knowlton,  July  27,  1888.  The  figured  specimen  was  collected 
by  George  M.  Wright,  July  7,  1885,  on  the  top  of  Mount  Everts,  ou  the 
west  face. 

Malapoenna  weediana?  Kn. 

Malapoenna  weediana  Kn.:  Bull.  IT.  S.  Geol.  Surv.  No.  152,  p.  142,  1898. 

Litsea  weediana  Ku.:  Bull.  U.  S.  Geol.  Surv.  Xo.  105,  p.  55,  1893. 

Teranthera  sessiliflora  Lx.  ex.  p.     Lesijuereux :  Teit.  FL,  p.  217,  PL  XXXV,  fig.  9, 1878. 

There  is  a  single,  nmch  broken  fragment  that  appears  to  belong  to  this 
species.     It  is  too  fragmentary  to  be  positive. 

Habitat:  Top  of  Mount  Everts,  west  face;  collected  by  George  M. 
Wright,  July  7,  1885. 

Paliurus  minimus  n.  sp. 
PL  LXXVII,  flgs.  7-9. 
Leaves  thin,  membranaceous,  nearly  circular  in  outline,  very  slightly 
wedge-shaped  at  base,   rounded    and  obtuse  at   apex;    margin   perfectly 


660  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

entire;  equally  five-nerved  from  the  base,  with  an  occasional  branching  of 
the  outside  nerve,  making  the  leaf  appear  seven-nerved;  midnerve  thin, 
straight,  passing  to  the  upper  border;  other  nerves  of  same  strength, 
camptodi'ome,  arching  in  bows  and  joining  the  midvein  or  midrib;  lateral 
branches  few,  at  an  acute  angle;  finer  nervation  not  j^reserved. 

This  fine  characteristic  species'  is  represented  by  a  number  of  fairly 
well  preserved  examples,  the  best  of  which  are  figured.  They  are  about 
2.8  cm.  in  length  and  about  the  same  in  width.  They  are  nearly  circular 
in  shape,  l^eing  slightly  wedge-shaped  at  the  base,  bnt  perfectly  obtuse  at 
the  apex.  The  nerves  are  all  of  about  equal  strength  and  divide  the  space 
of  the  blade  into  approximately  equal  areas.  They  occasionally  branch, 
especially  the  thin  central  ones. 

This  species  is  undoubtedly  quite  closely  allied  to  several  described 
forms.  From  Paliurus  colomhl  Heer^  it  differs  in  shape  and  nervation.  It 
is  very  much  like  some  of  the  small  leaves  of  P.  zizyphoides  Lx.,"  from  the 
Laramie  of  Erie,  Colorado,  and  Black  Buttes,  Wyoming,  but  they  differ  in 
having  the  nerves  arising  from  the  midrib  well  above  the  base  of  the  blade. 
The  species  under  discussion  has  precisely  the  same  shape  and  much  the 
same  nervation  as  Zizijphus  meekii  Lx.,^  bnt  this  differs  essentially  in  having 
a  dentate  margin. 

On  the  Avhole  it  may  be  characterized  by  its  circular  shape,  entire 
margin,  and  five  nerves  from  the  base. 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek,  Yellowstone 
National  Park;   collected  by  Arnold  Hague,  August  10,  1887. 

Paliurus  zizyphoides?  Lx. 

PL  LXXVIII,  fig.  3. 
Paliuriis  zizyphoides  Lx. :  Tert.  El.,  p.  274,  PI.  LI,  figs.  1-6, 1878, 

This  very  small  leaf  is  broken  at  the  base  and  otherwise  obscure,  but 
seems  to  belong  to  this  species. 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek;  collected  by 
Arnold  Hague,  August  10,  1887. 

■Lesquereux,  Tert.  Fl.,  p.  27:?,  PI.  L,  fig8.  13-17. 

=  Op.cit.,Pl.  LI,  fig.  2. 

'Op.  cit.,  p.  275,  PI.  LI,  figs.  10-14. 


FOSSIL  FLORA.  661 

DOMBEYOPSIS    PLATANOIDES    Lx. 

PL  LXXVIII,  fig.  1. 
Dombeyopsis platanoides  Lx.:  Tert.  FL,  p.  254,  PL  XLVII,  fif>,s.  1,  2,  1878. 

A  siuju-le  specimen. 

Habitat:  Top  of  Mount  Everts,  west  face;  collected  by  Greorge  M. 
Wright,  July  7,  188.5. 

Andromeda  grayana  Heer. 

Andromeda  grayana  Heer:  FL  Foss.  Alaska,  p.  34,  PL  VIII,  fig.  5.  Lesquereux: 
Tert.  Fl.,  p.  234,  PL  XL,  fig.  4.  Knowlton:  Bull.  U.  S.  GeoL  Surv.  No.  105, 
p.  56. 

Habitat:  Mount  Everts,  near  the  summit  of  the  west  end;  collected 
by  F.  H.  Knowlton,  July  27,  1888. 

Teapa!  microphylla  Lx. 

PL  LXXVIl,  figs.  3,  4. 

Trapaf  microphylla  Lx.:  Tert.  FL,  p.  295,  PL  LXI,  figs.  16-17a.  Ward:  Types  Lara- 
mie FL,  p.  64,  PL  XXVIII,  figs.  2-5. 

This  is  undoubtedly  the  same  species  as  that  figured  by  Lesquereux 
from  Point  of  Rocks,  Wyoming,  and  by  Ward  from  Burns  Ranch,  on  the 
lower  Yellowstone.  It  shows  more  the  habit  of  the  specimen  figured  by 
Ward,  but  has  the  general  nervation  of  all  the  specimens  referred  to  this 
species. 

In  fig.  15ffl  of  Tertiary  Flora  the  leaflets  are  petioled,  while  in  fig.  15 
they  are  clearly  similar  to  Professor  Ward's  examples. 

These  curious  but  well-marked  leaves  can  not  possibly  belong  to  the 
genus  Trapa  as  we  now  understand  it,  but  as  I  am  at  present  absolutely 
unable  to  suggest  any  other  afiinity,  I  can  do  nothing  but  leave  their 
correct  determination  to  be  settled  by  future  workers. 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek;  collected  by 
Arnold  Hague,  August  10,  1887. 


662  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

DiosPYRos  STENOSEPALA  Heer. 

Biospyros  stenosepala  Heer.    Lesquereux :  Fifth  Ann,  Kept.  U.  S.  Geol.  and  Geog. 
Surv.  Terr.,  p.  296,  1871  (1872). 

Habitat:  "Divide  between  the  source  of  Snake  River  and  the  southern 
shore  of  Yellowstone  Lake." 

Fraxinus  denticulata  Heer. 

PL  LXXVIII,  fig.  C. 

Fraxinus  denticulata  Heer:   Fl.  Foss.  Arct.,  Vol.  I,  p.  118,  PL  XVI,fig.4;  PL  XLVII, 
fig.  2.    Lesqnereux :  Tert.  FL,  p.  228,  PL  XL,  figs.  1, 2. 

Several  well-preserved  specimens  that  are  referred  with  certainty. 
Besides  these  there  are  several  other  well-preserved  examples,  of  which  the 
one  figured  is  perhaps  the  best,  that  are  somewhat  larger  than  the  types, 
but  still  appear  to  belong  with  them.  The  nervation  is  obscure,  but  the 
shape  and  toothed  margin  are  quite  similar. 

Habitat:  Mount  Everts,  near  summit  of  the  west  end;  collected  by 
F.  H.  Knowlton,  July  27,  1888. 

Viburnum  rotundifolium  Ix. 

PL  LXXVII,  tig,  10;  PI.  LXXVIIL  figs.  2,  8,  9. 

Tihurmim  rotundifolium  Lx.:  Tert.  FL,  p.  225,  PL  XXXVIL  fig.  12;  PL  XXXVIII, 
fig.  10;  PLLXI,  fig.22. 

There  is  considerable  difference  in  size  among  the  specimens,  but  they 
seem  to  belong  together,  and  to  approach  quite  closely  to  Lesquereux's 
species.  The  small  leaf  shown  in  fig.  9,  for  instance,  is  certainly  the  same 
as  the  plant  figured  by  Lesquereux  (loc.  cit.,  PI.  LXI,  fig.  22),  while  fig.  8 
is  like  fig.  10,  PI.  XXXVin  (loc.  cit.). 

Habitat:  North  of  Piny  on  Peak,  on  Wolverine  Creek;  collected  by 
Arnold  Hague,  August  10,  1887. 


FOSSIL  FLORA. 


663 


Table  showing  geological  distribution  of  Laramie  plants. 


TellowstoDP  National 
Park. 

Outside. 

1 
> 

o 

6 
1 

> 

>   . 

5 

i. 

It 

J" 

1 

i 

a; 

d 

Q 

> 
3 

a 

-a 

1 

'3 
& 

■s 

1 

p 
£ 

X 
X 

Anemia  subcretacea  (Sap.)  Gard.  and  Ett. 

X 

X 

X 

xf 

X 

X 

Setiuoia  reiclienhachi  (Gein.)  Heer 

X 
X 

X 

X 

X 

X 
X 
X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

!  X 

1 

8 

7 

3 

5 

5 

i 

It 

2 

1 

a  Very  doubtful. 


DISCTTSSIOK  OF   LARAMIE   FLORA. 


It  will  be  observed  that  there  are  only  three  localities  within  the 
Yellowstone  National  Park  that  have  afforded  Laramie  plants,  viz :  Near  the 
summit  of  Mount  Everts,  the  valley  of  Wolverine  Creek,  and  the  more  or 
less  doubtful  locality  known  as  "divide  between  the  source  of  Snake  River 
and  the  southern  part  of  the  Yellowstone  Lake."  It  has  not  been  possible 
to  relocate  the  latter  place,  but  as  it  is  in  a  region  in  which  Laramie  strata 
are  known  to  occur,  and  several  of  the  species  represented  have  since  been 
found  in  Laramie  strata  outside,  it  is  assumed  to  be  correct. 


664     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

This  flora  embraces  only  18  species,  of  which  number  8  are  confiuecl 
to  the  Mount  Everts  locahty,  7  to  Wolverine  Creek,  and  3  to  the  above- 
mentioned  doubtful  locality. 

Of  the  8  species  found  at  Mount  Everts,  1  (Pliragmites  falcata)  is 
described  as  new,  and  2  species  {Quercus  eUisiana  and  Bomheijopsls  i)lat- 
anoides)  have  never  before  been  found  outside  of  the  so-called  Bozeman 
Laramie.  The  2  species  regarded  as  doubtful  (Mijrica  holanderi  and 
M(d(tpoenna  weediana)  depend  on  a  single  fragment  each  and  are  obviously 
of  no  value  in  determining  the  age.  They  are  found  normally  in  much 
higher  horizons  Of  the  3  remaining  species.  Sequoia  reichenhachi  lias 
been  found  in  the  Livingston  beds,  but  is  also  found  in  the  true  Laramie, 
and  abundantly  in  still  older  strata.  Andromeda  grayana  and  Fraxiniis 
denticidata  have  been  found  in  both  Laramie  and  Livingston  beds  in  the 
Bozeman  area. 

The  evidence  of  the  fossil  plants  confirms  that  derived  from  the  study 
of  the  stratigraphy,  namely,  that  the  beds  near  the  summit  of  Mount 
Everts  are  of  Laramie  age. 

Of  the  7  species  from  Wolverine  Creek,  3 — Asplenium  hagiiei,  Onoclea 
minima,  and  Paliurus  minimus — are  described  as  new.  The  first  of  these 
does  not  appear  to  have  any  very  close  relatives  in  North  America,  but 
apparently  finds  its  nearest  analogue  in  certain  species  from  the  Creta- 
ceous of  Greenland.  Onoclea  minima,  on  the  other  hand,  is  very  close  indeed 
to  a  fern  from  Point  of  Rocks,  Wyoming,  that  has  been  described  under  the 
manuscript  name  of  Woodwardia  crenata.  The  Wyoming  plant  depends  on 
two  or  three  small  fragments,  which,  as  pointed  out  under  the  diagnosis  of 
Onoclea,  are  hardly  sufficient  to  properly  characterize  it.  It  is  quite  possi- 
ble that  when  new  material  shall  be  obtained  these  two  plants  will  be  found 
identical.  Paliurus  minimus  is  perhaps  nearest  to  P.  sizyphoides  from  Black 
Buttes,  Wyoming,  and  Erie,  Colorado.  The  4  remaining  species  are 
distributed  as  follows :  Sequoia  langsdorfii  is  represented  by  1  small  branch- 
let,  and  the  identification  is  probably  correct,  as  it  is  an  easily  recognized 
species.  It  has  a  wide  geological  and  geographical  distribution,  being 
especially  abundant  in  the  lower  Fort  Union  beds.  Paliurus  minimus  is 
doubtfully  identified  in  this  material.  As  stated  above,  it  is  a  true  Lara- 
mie species.  Viburnum  rotundifolium  is  also  a  Laramie  species.  It  has 
never  before  been  found  outside  of  the  type  locality,  which  is  Point  of 


FOSSIL  FLORA.  605 

Rocks  and  lilack  liuttes,  ^yy<)lniIlli•.  The  most  interestiuf,'-  species  is  Trapa? 
mkroplnjUa.  It  is  rej)reseutetl  by  several  perfectly  characteristic  specimens. 
This  species  was  first  described  from  Point  of  Rocks,  Wyoming,  and  was 
found  later  by  Professor  Ward  in  lowest  Fort  Union  beds,  near  the  mouth 
of  the  Yellowstone  River.  The  Wolverine  Creek  specimens  approach 
closest  to  Professor  Ward's  specimens.  Professor  Ward  is  of  the  ojiinion 
that  these  lower  beds  represent  the  Laramie,  since  the  plants  in  them  differ 
from  those  in  the  undoubted  Fort  Union  beds. 

The  three  species  from  the  divide  between  Snake  River  and  the 
southern  part  of  YelloAvstone  Lake  are  of  little  value  in  determining-  the 
age.  Geonomifes  schimperi  has  never  been  found  in  any  other  locality,  and 
Diospi/ros  stenosepala  is  very  doubtful  indeed.  It  has  not  since  been  col- 
lected, and  the  specimen  on  which  Lesquereux  based  his  determination  can 
not  now  be  found.  The  only  remaining  species.  Anemia  suhcretacea  or 
Gymnogramma  haydenU  of  Lesquereux,  has  a  wide  distribution,  having  been 
found  in  the  Laramie,  Denver,  and  Eocene. 

DESCRIPTION  OF  FOSSIL  PLANTS  FROM  THE  TERTIARY  OF  THE 
YELLOWSTONE  NATIONAL  PARK. 

PLANTS,  EXCLUSIVE    OF   FOSSIL  WOOD. 

FILICES. 

WOODWARDIA    PREAREOLATA  n.  sp. 
PL  LXXIX,  flg.  1, 

Frond  pinnate;  pinna?  alternate,  lanceolate,  with  slightly  undulate 
margins,  connate  at  their  bases,  forming  a  broad  wing  on  the  rachis;  nerva- 
tion strongly  reticulated,  consisting  of  one  or  two  rows  of  long  lacunar 
next  to  the  main  rachis  and  along  the  secondary  rachis,  and  the  remainder 
forming  large  polygonal,  slightly  elongated,  meshes. 

Unfortunately  the  specimen  figured  represents  the  only  example  found. 
It  is  far  from  perfect,  being  only  a  segment  from  the  middle  of  a  frond, 
and  consequently  no  idea  can  be  gained  of  the  outline  of  the  whole  frond. 
The  segment  of  the  main  rachis  is  8  cm.  long.     The  pinnje  are  regularly 


Qid6  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

alternate — that  is,  are  the  same  distance  apart.  They  are  at  least  6  cm.  in 
length  and  2  cm.  in  width.  The  fnll  length  and  form  of  the  apex  could  not 
be  determined.     The  nervation  is  well  shown  in  the  figure. 

This  species  is  undoubtedly  very  closely  related  to  the  living  Woocl- 
wardia  areolata  (L.)  Moore — so  closely,  in  fact,  that  it  is  hardly  possible  to 
separate  them  satisfactorily.  The  pinna?,  are  alternate,  of  the  same  shape, 
and  have  identical  nervation  in  both.  The  only  difference  is  that  the 
margir  s  of  the  pinnjB  are  entire  in  the  fossil  and  more  or  less  serrate  in  the 
living  species.  It  is  possible  that  more  material  of  the  fossil  form  would 
show  differences  in  this  respect  and  bring  them  absolutely  together. 

This  new  fossil  species  much  resembles  Onoclea  sensibilis  fossilis  New- 
berry, from  the  Fort  Union  group,  but  it  differs  in  having  strictly  alternate 
pinuffi  that  are  as  far  apart  as  it  is  possible  to  be.  The  pinnje  are  also  without 
lobes  of  any  kind,  being  only  slightly  undulated.  The  nervation  differs 
slightly  in  producing  more  elongated  areolae  in  0.  sensibilis  fossilis. 

In  nervation  W.  preareolata  resembles  W.  latiloba  Lx.,^  from  the  Den- 
ver group,  but  differs  markedly  in  having  the  pinnae  unlobed. 

Habitat:  Northeast  side  of  Crescent  Hill,  opposite  small  pond;  col- 
lected by  F.  H.  Knowlton  and  G.  E.  Culver,  August  2,  1888. 

AsPLENIUiM    IDDINGSI    U.    Sp. 
PI.  LXXIX,  figs.  2,3;  PI.  LXXX,  figs.  9,10. 

Frond  large,  at  least  twice  pinnate;  main  rachis  thick,  slightly  zigzag; 
pinna;  alternate,  remote,  standing  at  an  angle  of  30°  to  45°,  long-lanceolate, 
tapering  to  a  rather  slender  apex,  rachis  strong,  often  abruptly  curved 
upward,  cut  into  numerous  alternate,  oblong,  obtusely-acuminate  pinnules 
with  upward-turning  points;  nervation  of  pinnules  simple,  consisting  of  a 
slender  inidnerve  and  about  9  pairs  of  unforked,  close,  parallel  branches, 
which  are  slightly  arched  forward  in  passing  to  the  borders;  sori  oblong, 
nearer  the  margin  than  the  midnerve. 

This  fine  species  is  represented  by  a  large  number  of  well-preserved 
specimens.  It  appears  to  have  been  a  very  large  fern,  possibly  several 
times  pinnate,  but  none  of  the  specimens  show  the  larger  connections.  The 
largest  rachis  with  pinnae  attached  is  4  mm.  thick,  but  on  the  same  stone,  and 


'Teit.  I-l.,  p.  54,  PI.  Ill,  figs.  1,  la. 


FOSSIL  FLORA.  667 

evidently  of  the  same  species,  are  stems  or  vachises  fully  S  mm.  thick.  There 
is  some  evidence  to  indicate  that  they  were  combined  into  a  very  large 
frond,  but  it  is  not  conclusive.  The  longest  example  is  about  20  cm.  long 
and  spreads  about  9  cm.  The  longest  pinna  (PI.  LXXX,  fig.  9)  is  preserved 
for  9  cm.  and  still  lacks  the  terminal  portion.  The  pinnse  vary  in  width 
from  10  to  24  mm.,  depending  upon  the  portion  taken. 

The  pimafe  are  cut  into  oblong  acuminate  pinnules,  the  sinus  some- 
times extending  to  within  one-third  of  their  length  of  the  base,  but  usually 
to  about  half  the  length.  Pinnules  with  a  slender  midnerve  and  7  to  10, 
usually  9,  pairs  of  close,  unforked  nerves.  The  lower  nerves  of  adjoining 
pinnules  unite  at  a  low  angle  and  pass  upward  and  end  in  the  sinus. 

Fruit  dots  were  observed  only  on  one  small  fragment  (PI.  LXXIX, 
fig.  2).  Tliey  are  obscure,  but  as  nearly  as  can  be  made  out  they  are 
oblong  and  near  the  margin  of  the  pinnules.  Unfortunately  none  of  the 
larger  specimens  are  fruiting,  but  apparently  they  all  belong  to  the  same 
species. 

I  do  not  recall  any  fossil  species  to  which  this  seems  to  be  allied.  A 
number  that  have  been  described  resemble  it,  but  none  closely  enough  to 
constitute  specific  similarit}'. 

I  have  named  this  species  in  honor  of  Prof.  Joseph  P.  Iddings,  of  the 
University  of  Chicago,  who  pointed  out  the  locality  which  afi"orded  the  best 
specimens. 

Habitat:  Yellowstone  River,  above  mouth  of  Hellroaring  Creek  (figs. 
3,  10);  bank  of  Yellowstone,  one-half  mile  below  mouth  of  Elk  Creek,  base 
of  bluff  (figs.  2,  9);  collected  by  F.  H.  Knowlton  from  Fossil  Forest  Ridge, 
bed  No.  6,  "Platanus  bed,"  August,  1888.  One  specimen  collected  by 
Lester  F.  Ward  and  F  H.  Knowlton,  August,  1887. 

ASPLENIUM    MAGNUM  n.  Sp. 

PI.  LXXIX,  figs.  5-8,  Sa. 

Frond  simple,  pinnatifid,  sometimes  nearly  pinnate  below,  long  lance- 
olate in  outline,  from  a  regular  obtusely  wedge-shaped  base,  and  extending 
into  a  long  slender  apex;  cut  into  numerous,  mainly  alternate,  ovate,  sharp- 
pointed  lobes,  those  at  the  base  being  sometimes  cut  nearly  to  the  rachis, 
those  above  less  and  less  until  the  apex  is  nearly  entire;  nervation  of  the 


668  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

lobes  or  pinnules  consisting  of  a  strong  niidnerve  passing  to  the  tip,  and 
6  or  8  pairs  of  alternate  once-forked  lateral  nerves;  fruit  dots  not  seen. 

This  large  and  striking  species  is  the  most  abundant  fern  found  in  the 
Park.  It  is  represented  in  the  collection  by  fully  40  specimens,  all  from 
one  locality.  The  largest  example  (fig.  7)  is  17.5  cm.  long  and  2.5  cm. 
broad,  and  still  lacks  the  terminal  portion.  It  has  a  stipe  8  mm.  long  and  2 
mm.  thick.  Fig.  5  is  16  cm.  long  and  23  mm.  broad,  and  lacks  both  base 
and  apex.     Some  of  the  fronds  must  have  been  fully  25  cm.  long. 

This  species  is  well  characterized.  It  has  a  thick  grooved  rachis  (1mm.) 
and  a  short  thick  stipe.  The  lobes  or  pinnules  are  irregularly  ovate,  sepa- 
rated usually  to  the  middle  by  a  sharp  sinus,  and  having  a  sharp  upward- 
pointing  apex.  The  nervation  consists  of  a  strong  midnerve  ending  in  the 
apex  and  about  7  pairs  of  alternate  forked  branches.  As  in  the  former 
species,  the  lower  nerves  of  adjacent  lobes  unite  and  pass  upward  to  the 
sinus.     Occasionally  there  may  be  an  unforked  nerve,  but  it  is  the  exception. 

This  species  is  associated  in  the  same  beds  with  A.  iddingsi  and  much 
resembles  it,  differing,  however,  in  having  apparently  simple  fronds  that 
are  uniformly  larger  than  the  pinuse  of  the  former  species,  and  in  having 
the  nervation  of  the  lol^es  always  forking  (see  fig.  8  and  8a).  It  difi'ers 
further  in  having  a  short  stipe  and  in  having"  the  upper  portion  nearly  or 
quite  entire. 

The  correctness  of  tliis  generic  reference  is  of  course  a  matter  of  more 
or  less  doubt,  as  no  fruiting  specimens  have  been  found,  but  the  fern  appears 
to  be  allied  generically  at  least  to  A.  iddingsi.  It  is  certainly  a  well-marked 
species  for  geological  purposes. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
Yellowstone  National  Park,  at  base  of  bluff;  collected  by  F.  H.  Knowltou, 
August,  1888. 

AsPLENiuM  ergsumI  (Lx.)  Kn. 

PI.  LXXX,  fig.  6. 

Asplenium  efosum  (Lx.)  Ku.:  Bull.  U.  S.  Geol.  Surv.  No.  152,  p.  45, 1898. 
Pteris  erom  Lx.:  Tert.  Fl.,  p.  53,  PI.  lY,  fig.  8. 

This  appears  to  be  the  same  as  described  by  Lesquereux,  but  is  obscure 
and  difficult  to  make  out.  None  of  the  specimens  are  complete,  and  all  have 
the  nervation  very  poorly  preserved.     The  margin  seems  more  erose  than 


FOSSIL  FLORA.  069 

tlie  type,  and  the  nerves  may  not  foi'k.  It  is  possible  that  it  is  a  new 
species,  but  until  better  material  can  be  obtained  T  have  preferred  to  retain 
the  specimens  under  this  species. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek; 
collected  by  F.  H.  Knowlton,  August  13,  1888  (fig.  6).  Yellowstone  River, 
wall  of  canyon  above  mouth  of  Hellroaring  Creek;  collected  by  W.  H. 
Weed,  October  13,  1887. 

ASPLENIUM    REMOTIDENS    n.  sp. 
PI.  LXXX,  fig.  7. 

Pinna3  large,  coriaceous,  broadly  lanceolate,  taper  pointed,  obtuse 
and  unequal  sided  at  base;  margin  with  few  remote  sharp  teeth;  midvein 
strong;  lateral  veins  at  an  angle  of  about  45°,  simple  or  forking  once  some 
distance  above  the  midvein;  sori  not  seen. 

The  very  perfect  example  figured  is  the  only  specimen  obtained.  It 
is  11  cm.  in  length  and  2.5  cm.  broad.  It  is  broadly  lanceolate  with  a 
slender  tapering  apex  and  obtuse  unequal-sided  base.  The  nervation  is 
very  obscure.  It  is  probable  that  all  of  the  lateral  veins  fork,  but  it  was 
not  possible  to  make  this  out,  and  the  figure  shows  many  as  unforked. 
The  ones  that  are  made  out  to  have  the  fork  show  it  some  distance  above 
their  base. 

This  species  is  very  closely  allied  to,  if  not  indeed  identical  with, 
Asplenium  erosum  (Lx.)  Ku.,^  from  the  Denver  formation  of  Colorado.  It 
has  exactly  the  same  shape,  but  differs  in  having  few  remote  teeth,  and  in  the 
branching  of  the  veins.  In  A.  erosum  the  veins  fork  at  the  base  and  occa- 
sionally above  the  middle.  In  any  case  the  species  are  very  close  together 
and  may  be  combined  at  any  time  if  future  material  from  the  Yellowstone 
National  Park  shows  variation  in  the  characters  now  relied  upon  for  their 
separation. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  base  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Dkyopteris  weeuii  n.  sp. 
PI.  LXXX,  fig.  8;  PL  LXXXI,  fig.  2. 
Frond  twice  pinnate;  pinnse  probably  lanceolate  in  outline;  pinnules 

'  Under  Pteria  eroea  Lx.,  Tert.  Fl.,  p. 53,  PI.  IV,  fig.  8;  Cret.  and  Tert.  Fl.,  p.  121,  PI.  XIX,  fig.  1. 


670     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

opposite  or  subopposite,  nearly  at  right  angles  to  the  rachis,  long'-lanceolate, 
rather  abruptly  acuminate,  cut  to  within  a  ver3"  short  distance  of  the  rachis; 
nervation  simple,  consisting  of  a  strong  straight  midvein  and  numerous 
(about  20)  pairs  of  opposite,  parallel,  unbranched,  lateral  nerves;  fruit 
dots  small,  round,  on  the  backs  of  the  nerves  midway  between  the  midvein 
and  the  margin. 

This  beautiful  species  is  represented  by  several  specimens,  the  best  of 
which  is  shown  in  iig.  8.  The  pinnules  are  opposite  or  subopposite.  They 
are  long,  slender,  and  pointing  upwaixl.  The  nervation  is  very  regular, 
consisting  of  the  strong  midvein  and  18  to  20  or  more  pairs  of  opposite 
parallel  veins.  The  fruit  dots  are  distinct,  though  small,  and  borne  on  the 
veins  midway  between  the  midvein  and  margin. 

This  species  is  closely  allied  to  Lastrea  r/oldiana  (Lx.)  Kn.,'  from  the 
Denver  beds  of  Grolden,  Colorado.  It  does  not  so  closely  resemble  the 
figure  given  by  Lesquereux  as  it  does  certain  forms  that  have  been  referred 
to  it  in  my  forthcoming  monograph  of  the  Laramie  and  allied  formations. 
The  type  of  the  species  is  described  by  Lesquereux  as  having  5  to  7  pairs 
of  nerves,  while  the  forms  that  I  have  referred  to  it  have  10  pairs,  with 
no  other  apparent  difiPerence.  Bryopterls  tveedii,  as  stated,  has  18  to  20  or 
more  pairs.  The  pinnules  are  from  10  to  16  mm.  long  and  about  5  mm. 
broad,  whereas  those  of  L.  goldiana  are  only  7  to  9  mm.  long  and  3  or  4 
mm.  broad. 

From  this  it  is  clear  that  these  two  species  are  quite  closely  related, 
and  possibly  a  larger  series  of  specimens  might  show  them  to  be  identical, 
but  for  the  present  it  is  best  to  regard  them  as  different. 

I  have  named  this  species  in  honor  of  Mr.  Walter  Harvey  Weed,  by 
whom  the  first  specimens  were  collected. 

Habitat:  Yellowstone  River,  breccia  in  wall  of  canyon  above  mouth 
of  Hellroaring  Creek  (PI.  LXXXI,  fig.  2);  collected  by  Walter  Harvey 
Weed,  October  13,  1887.  Cliff  on  Yellowstone  River  (left  hand),  short 
distance  above  mouth  of  Hellroaring  Creek  (PI.  LXXX,  fig.  8) ;  collected 
by  F.  H.  Knowlton,  August  10,  1888. 

'This  was  first  called  Aapidium  yoldianum  by  Lesquereux  (Seventh  Ann.  Kept.,  1873  p.  393),  but  was 
later  cbauged  to  Laeirea  {Gomoplvri:,)  ijoldiana  (cf.  Tert.  Fl.,  p.  56,  PI.  IV,  tig.  13). 


lOSSlL  FLORA.  671 

Drvoptekis   XANTHOLITHENSE   U.   sp. 
PI,  LXXXI,  lig.  1. 

Frond  pinnate?;  piniife  lanceolate;  pinnules  opposite, lanceolate-deltoid, 
obtuse,  cut  to  within  one-third  of  their  length  of  the  base,  much  arched 
ui)\vard  at  the  point;  nervation  simple,  consisting  of  well-marked  midvein 
and  9  or  10  pairs  of  opposite,  parallel,  unbranched  lateral  veins;  sori  large, 
round,  on  the  backs  of  the  veins  at  about  one-third  of  their  length  from 
the  midvein. 

Of  this  well-marked  species  the  single  specimen  figured  was  the  only 
one  found.  It  is  not  preserved  entire,  the  fragment  being  about  5  cm.  in 
length.  There  is  therefore  no  means  of  knowing  whether  or  not  it  was 
simple  or  compound.  The  portions  of  the  pinnae  preserved  are  of  the  same 
Avidth  throughout,  showing  that  they  probably  came  from  the  middle  por- 
tion. The  pinnules  are  opposite  and  arise  at  an  angle  of  30°  or  40"^  from 
the  rachis.  They  are  lanceolate-deltoid  in  shape,  and  about  12  mm.  long 
and  5  nun.  broad,  being  much  arched  upward  at  the  extremity.  The  fruit 
dots  are  large,  round,  aud  placed  on  the  backs  of  the  veins  near  the  mid- 
vein. 

This  species  is  allied  to  Dryopteris  iveedii,  from  which  it  clearly  differs 
in  having  much  shorter,  arching  pinnules,  only  9  or  10  pairs  of  nerves,  and 
larsrer  fruit  dots  which  are  nearer  the  midvein.  The  nervation  is  the  same 
in  character,  but  differs,  as  stated,  in  number  of  pairs  of  veins. 

From  Lastrea  goldiana  this  species  differs  in  much  the  same  manner. 
It  has  more  arching  pinnules,  and  is  quite  different  in  general  appearance. 
The  number  of  pairs  of  nerves  is,  however,  about  the  same ;  all  of  which 
goes  to  show  that  these  three  species  are  closely  related. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  6, 
"Platanus  bed;"  collected  by  Lester  F.  Ward  and  F.  H.  Knowlton,  August 
19,  1887. 

DeVAI.LIaI    MONTANA  11.  Sp. 
PI.  LXXIX,  fig.  4. 

Frond  thin,  twice  pinnate,  possibly  more  compounded;  rachis  strong; 
pinnae  alternate,  lanceolate,  ending  in  a  sharp,  hair-like  point;  cut  into  5 


672  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

or  6  lobes  or  pinnules,  the  sinuses  toward  the  base  going  nearly  to  the 
secondary  rachis,  more  entire  near  the  apex;  lower  pinnules  or  divisions 
2  or  3  toothed,  all,  but  especially  the  terminal  pinnules,  ending  in  long, 
slender,  outward-pointing  teeth;  nervation  simple,  consisting  of  a  strong- 
secondary  rachis  with  rather  delicate  nerves  pointing  to  the  pinnules;  the 
nerves  near  the  base  two  or  three  times  branching,  the  branches  entering 
the  teeth;  nerves  near  the  extremity  unbranched. 

The  small  fragment  figured  represents  all  that  was  found  of  this 
species.  It  is  only  about  30  mm.  long  and  25  mm.  broad,  the  pinnae  being 
17  mm.  in  length  and  approximately  10  mm  in  width. 

Notwithstanding  the  smallness  of  the  fragment,  there  is  enough  to 
show  that  it  differs  markedly  from  any  other  form  in  the  Park  flora.  I  am 
quite  at  loss,  however,  to  indicate  its  generic  affinities.  I  have  placed  it 
under  Devallia  tentatively,  and  can  only  hope  that  subsequent  material  will 
serve  to  fix  more  satisfactorily  its  position. 

Habitat:  Fossil  Fore.st  Ridge,  Yellowstone  National  Park,  bed  No. 
3,  "Magnolia  bed;"  collected  by  Lester  F.  Ward  and  F.  H.  Knowlton, 
August  16-19,  1887. 

Lygodiuji  kaulfusii  Heer. 

PI.  LXXX,  figs.  1-3. 
Lycjodium  neuropter aides  Lx.:  Tert.  Fl.,  p.  Gl,  PI.  V,  tigs.  4-7;  PI.  VI,  fig.  1. 

According  to  Gardner,^  the  Lygodium  neuropteroides  of  Lesquereux  is 
absolutely  identical  with  L.  haulfusii  of  Heer.  Lesquereux  was  shown 
specimens  of  the  true  L.  kaiilfasii  from  the  British  Eocene  and  pronounced 
them  "positively  identical"  with  his  species  from  the  Green  River  group 
and  later  formations.  A  glance  at  Gardner's^  figures  shows  that  it  is  impos- 
sible to  separate  the  American  specimens. 

This  species  was  found  at  two  localities  in  the  Yellowstone  National 
Park,  namely,  on  the  Yellowstone  River  below  the  mouth  of  Elk  Creek, 
and  on  the  north  bank  of  the  Lamar  River  between  Cache  and  Calfee 
creeks.  The  specimens  from  below  Elk  Creek  are  in  hard,  rather  coarse- 
grained rock  at  the  base  of  the  section.     They  are  very  large,  having  lobes 

1  Brit.  Eoo.  Fl.,  Pt.  1,  Filices,  p.  47.  *0p.  cit.,  PI.  VII,  figs.  1, 3-8  ;  PI.  X,  fig.  11. 


FOSSIL  FLORA.  673 

8  em.  long'  and  2  cm.  broail,  and  A'ery  much  resemble  a  figure  of  this  species 
given  by  Newberry, '  from  the  Pacific  coast. 

The  specimens  from  the  Lamar  River  ai"e  much  slendei'er,  being  7  cm. 
long  and  less  than  1  cm.  broad.  Some  of  them,  as  fig.  2,  are  very  small  and 
delicate.  In  nervation  the  specimens  from  both  localities  agree  perfectly, 
as  they  do  with  European  specimens. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  base  of  section;  collected  by  F.  H.  Knowlton,  August  13,  1888.  North 
bank  of  Lamar  River,  between  Cache  and  Calfee  creeks;  collected  by  F.  H. 
Knowlton,  August  21,  1888. 

OSMUNDA  AFFINIS  Lx. 

PI.  LXXX,  figs.  4,  5. 
Omiunda  affinis  Lx.:  Tert.  Fl.,  p.  (iO,  PI.  IV,  fiR.  1. 

The  Park  collection  contains  specimens  of  several  detached  pinnules 
that  it  seems  necessary  to  refer  to  this  species.  They  are  about  the  same 
size  as  Lesquereux's  type  specimen,  but  are  better,  in  that  they  show  the 
bases  of  the  pinnules. 

Li  the  collection  of  Denver  group  plants  recently  worked  up  there  are 
a  number  of  specimens  of  this  species,  some  of  which  are  very  fine.  One 
in  particular,  which  has  been  figured  for  the  forthcoming  monograph  of  the 
Laramie  and  allied  formations,  is  very  large  and  perfect.  It  has  a  long 
zigzag  rachis  with  numerous  sessile  pinnules  alternately  attached.  They 
have  a  distinctly  heart-shaped  base,  a  slightly  undulate  margin,  and  a 
tapering  but  obtuse  apex.  In  all  these  particulars,  as  well  as  in  nervation, 
the  Park  specimens  agree.  The  latter  are  a  little  shorter  than  the  Denver 
specimens,  and  one  is  a  trifle  broader,  but  the  differences  are  unessential. 
There  is  no  knowing  the  part  of  the  frond  from  which  they  came,  and  this 
may  readily  account  for  discrepancies. 

Habitat:  Southeast  side  of  hill  north  of  Lost  Creek,  Yellowstone 
National  Park,  bed  No.  1,  about  6,5.50  feet  altitude;  collected  by  F.  H. 
Knowlton,  August  5,  1888. 


ipiates.Pl.LXII,  fig.  1.    [Ined.] 
MON  XXXII,  PT  II 43 


674  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

EQUISETACEJ;. 

Equisetum  haguei  n.  sp. 
PI.  LXXXI,  flgs.  3.  4. 

Stem  simple,  striate,  articulate;  articulations  rather  long;  sheaths 
short;  teeth  long,  appressed,  sharp-pointed. 

This  species  is  represented  by  numerous  fragments,  many  of  which, 
however,  show  the  sheaths.  The  stem  is  from  4  to  6  mm.  broad  and  the 
articulations  are  5  to  6  cm.  in  length.  It  is  plainly  striate,  with  usually  9 
ribs.  The  sheaths,  which  are  darker  in  color  than  the  stem,  are  6  or  7  mm. 
in  length  and  are  provided  with  closely  appressed,  very  sharp-pointed  teeth, 
about  3  mm.  long. 

If  there  are  8  or  9  ribs  now  visible  in  the  flattened  stems,  it  seems 
safe  to  assume,  inasmuch  as  they  were  cylindrical,  that  they  have  16  or  18 
ribs,  and  an  equal  number  of  teeth. 

It  was  at  first  supposed  that  these  specimens  could  be  referred  to  E. 
limosuni  L.  [see  following  species],^  as  identified  by  Lesquereux  from  mate- 
rial collected  by  Hayden  from  basaltic  rocks  near  the  Yellowstone  Lake ; 
but  an  examination  of  the  type  specimen  preserved  in  the  United  States 
National  Museum  (No.  41)  shows  that  they  can  not  be  the  same.  Lesque- 
reux's  specimen  has  only  4  or  5  ribs  \'isible,  making,  as  he  says,  about  10 
for  the  entire  diameter,  while  this  has  16  to  18,  and  possibly  as  many  as  20. 
The  segments  of  the  stem  are  only  about  1  cm.  in  length  in  Lesquereux's 
specimen  and  6  or  7  cm.  in  the  one  under  discussion.  The  sheaths  are 
also  longer  and  the  teeth  sharper  in  E.  haguei. 

Among  living  species  this  seems  to  approach  closely  to  E.  Jimosum  L.; 
more  closely,  in  fact,  than  does  the  specimen  referred  to  E.  Umosum  by 
Lesquereux. 

I  have  named  this  species  in  honor  of  Mr.  Arnold  Hague,  who  pointed 
out  the  locality  where  it  was  found. 

Habitat:  Southeastern  end  of  hill  north  of  Lost  Creek,  Yellowstone 
National  Park,  bed  No.  5;  collected  by  F.  H.  Knowlton,  1888. 


'Fifth  Aun.  Kept.  U.  S.  Geol.  and Geog.  Surv.  Terr.,  1871  (1872),  p.  299;  Tert.  PI.,  p.  69,  PI.  VI,  tig.  5. 

« 


FOSSIL  FLOKA.  675 

Equisetum   LESQUKKEUXII    Kll. 

Eqiiisetinii  Ivsquereu.rii  Kn.:  Bull.  U.  S.  (leol.  Siirv.  No.  15li,  j).  !)4,  1898. 
Equisetum  limonum  Limi.  Lescinereiix :  Fifth  Aim.  Rept.  U.  S.  Geol.  and  Geog.  Surv. 
Terr.,  1871  (1872),  p.  29!);  Tert.  Fl.,  p.  (!9,  PI.  VI,  tig.  5. 

As  already  stated  under  E.  hcujuei,  the  type  specimen  of  this  species  is 
in  the  United  States  National  Museum  (No.  41).  Tlie  figure  given  in  Tert. 
Fl.  (PI.  VI,  fig.  ,5)  is  much  more  perfect  than  the  specimen  proves  to  be. 
The  figure  shows  7  ribs  and  the  same  number  of  teeth,  which  would  make 
at  least  14  ribs  for  the  whole  stem.  The  specimen  shows  only  4  or  5  ribs, 
and  the  sheaths  and  teeth  are  very  obscure. 

As  it  seems  very  unlikely  that  it  should  belong  to  the  living  species, 
I  have  ventured  to  change  it,  and  have  named  it  in  honor  of  Professor 
Lesquereux. 

Habitat:   "Near  Yellowstone  Lake,  among  basaltic  rocks." 

Equisetum  canaliculatum  n.  sp. 
PI.  LXXXI,  figs.  6,  7. 

Stem  large,  about  50-ribbed;  articulate;  articulation  long;  sheath 
obscure,  but  apparently  short;  teeth  numerous,  short-appressed,  sharp- 
pointed. 

This  species  is  represented  by  the  two  fragments  figured  and  a  number 
of  other  doabtful  ones,  which  are  hardly  enough  to  properly  characterize 
the  species;  but  they  seem  to  differ  from  all  described  species  likely  to 
occur  in  this  region,  and  I  have  ventured  to  give  them  a  new  name. 
More  perfect  material  may  bring  out  the  relationship. 

The  longest  stem  (fig.  6)  is  about  6  cm.  in  length,  and  the  broadest 
on  that  piece  of  material  is  13  mm.  The  other  specimen  (fig.  7)  is  5  cm. 
long  and  21  mm.  broad.  The  ribs  are  distinct,  yet  not  specially  strong. 
They  number,  as  nearly  as  can  be  made  out,  about  25  on  a  side,  or 
approximately  50  for  the  entire  diameter.  The  length  of  the  segments  can 
not  be  made  out.  The  sheath  is  also  obscure.  It  maj^  be  that  fig.  6  repre- 
sents a  single  sheath;  if  so,  it  is  long,  but  the  other  specimen  gives  slight 
evidence  of  having  a  short  sheath.  The  teeth  are  short  and  appressed  and 
end  in  slender  points.  As  near  as  can  be  made  out,  there  are  about  25 
teeth  in  view,  or  something  like  50  for  the  whole  stem. 


676  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  two  stems  shown  in  the  upper  part  of  fig.  6  show  a  distinct  line 
of  tubercles  about  the  slight  constriction.  They  probably  represent  the 
lower  portions  of  the  stems. 

Habitat:  Yancey  Fossil  Forest,  beds  near  the  upright  stumps  (fig. 
6);  collected  by  F.  H.  Knowlton,  August  28,  1888.  End  of  Specimen 
Ridge,  opposite  Junction  Butte,  near  large  upright  stumps;  collected  by 
Lester  F.  Ward  and  E.  C.  Alderson,  August  25,  1887.  Yellowstone  River, 
one-half  mile  below  Elk  Creek,  at  base  of  bluff";  collected  by  F.  H. 
Knowlton,  August  27,  1888.  Cliff"  west  of  Fossil  Forest  Ridge;  collected 
by  Ward  and  Knowlton,  August  15,  1887, 

Equisetum  deciduum  n.  sp. 
PI.  LXXXI,  fig.  5. 

Stems  large,  many-ribbed,  articulate,  sheathed;  sheaths  short,  without 
teeth. 

This  form  is  represented  by  several  specimens,  all  very  fragmentary 
and  obscure.  It  has  the  stem  15  ram.  in  diameter,  and  the  sheath  14 
mm.  in  length.  The  diaphragm  is  clearly  shown  in  2  specimens,  and 
appears  to  have  been  thick.  The  sheath  is  close  and  without  teeth, 
which  probably  iuidcates  relationship  of  this  species  with  living  species, 
such  as  E.  hiemale,  E.  robustmn,  etc.,  having  deciduous  teeth. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  base  of  bluff'  (fig.  5);  collected  by  F.  H.  Knowlton,  August  27, 
1888.  Fossil  Forest  Ridge,  bed  No.  6,  "Platanus  bed;"  collected  by 
Ward  and  Knowlton,  August  19,  1887. 

CONIFER^}. 

PiNUS  GRACILISTROBUS  n    sp. 
PI.  LXXX,  fig.  12. 

Cone  lanceolate,  about  12  mm.  in  diameter  and  about  45  mm.  long 
(neither  base  nor  apex  preserved);  scales  in  7  or  8  rows,  regularly 
rhomboidal  in  shape,  about  6  mm.  in  transverse  and  about  5  mm.  in  vertical 
dimension;  scales  umbouate,  with  usually  3  slight  projections  on  the 
lower  angle. 

The  specimen  figured  is  the  only  one  found  of  this  specie^.     At  first 


FOSSIL  FLORA.  677 

sight  it  seems  hardly  possible  to  have  so  long  and  narrow  a  cone  with  so 
large  scales,  but  this  cone  is  preserved  entire — that  is,  it  has  been  pressed 
Hat,  and  b}'  turning  it  around  the  entire  series  of  scales  may  be  made  out. 
It  is  now  pressed  into  an  elliptical  shape,  with  a  long  diameter  of  aboiit 
12  mm.  and  a  short  diameter  of  about  5  nun.  Its  length,  as  already  stated, 
is  approximately  45  mm. 

I  have  not  been  able  to  find  any  fossil  species  with  which  this  can  be 
compared.  There  are  a  number  having  scales  of  much  the  same  shape, 
but  none  with  the  same  sized  cone. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  7, 
"Castaneabed;"  collected  by  Lester  F.  Ward  and  F.  H.  Knowltou,  August 
16-20,  1887. 

PiNUS    PREMURRAYANA    n.  sp. 
PJ.  LXXXII,  tig.  5. 

Cone  narrowiv  ovate-conical,  rounded  at  base  and  gradually  narrowed 
above  to  a  very  obtuse  and  rounded  apex;  scales  thick,  regularly  rhom- 
boidal,  transversely  wrinkled,  each  provided  with  a  rounded  blunt  umbo,  or 
possibly  with  a  short,  stovit  spine. 

This  species  is  represented  by  the  single  specimen  figured,  and  is  the 
most  perfectly  preserved  cone  I  have  ever  seen,  being  preserved  entire,  with 
little  or  no  distortion.  It  is  about  8  cm.  in  length.  It  is  broadest  at  base, 
where  it  is  about  2.5  cm.  in  diameter,  from  which  point  it  tapers  gradually 
to  the  apex,  where  it  is  about  1  cm.  in  diameter.  The  scales  are  very 
tightly  closed,  showing  that  with  little  doubt  the  cone  was  serotinous.  They 
are  quite  regularly  rhomboidal,  being  about  10  mm.  long  and  6  mm.  high, 
and  appear  to  have  been  transversely  wrinkled.  The  tip  is  thick,  raised, 
and  was  provided,  in  all  probability,  with  a  short,  stout  spine. 

In  seeking  the  probable  atfinities  of  this  cone,  a  number  of  interesting 
problems  are  presented,  first  of  which  is  the  state  of  maturity.  It  is,  of 
course,  a  well-known  fact  that  all  cones  are  tightly  closed  after  fertilization 
and  until  the  seeds  are  matured.  In  the  majority  of  cases  the  scales  open 
for  the  discharge  of  the  ripe  seeds,  yet  in  a  number  of  species  they  remain 
closed,  or  practically  so,  for  many  years.  The  seeds  of  these  serotinous 
cones  may  retain  their  vitality  for  years — a  provision  for  the  continuance 
of  the  species. 

Whether  the  cone  under  consideration  is  immature,  and  has  the  scales 


678  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

closed  on  this  account,  or  is  a  strictly  serotinous  form,  is  a  difficult  matter 
to  decide.  On  the  whole  it  seems  probable  that  it  was  nearly  or  quite 
mature,  and  should  be  placed  among  those  with  normally  closed  scales. 

The  next  question  is,  What  is  the  age  of  this  cone? — that  is,  is  it  a 
cone  of  a  recent  species  or  does  it  represent  an  extinct  form?  The  phe- 
nomena are  so  active  in  the  Park  at  the  present  time  that  it  is  perhaps 
possible  for  a  cone  of  this  kind  to  be  replaced  with  silica  within  a  com- 
paratively short  space  of  time.  It  however  came  from  a  part  of  the  Park 
where  the  hot-spi-ings  phenomena  have  ceased  for  a  long  period,  and  this 
lends  color  to  the  idea  that  it  is  not  of  very  recent  origin.  The  probability 
is,  therefore,  that  it  represents  an  extinct  rather  than  a  living  species. 

This  cone  clearly  belongs  to  the  pitch  pines  and  not  to  the  soft  or  white 
pines,  and  in  determining  its  affinities  this  latter  group  must  be  excluded. 
At  the  present  time  there  are  3  species  of  pines  growing  in  the  Yellow- 
stone National  Park,  as  follows:  Pinus  scopulorum,  P.JiexUis,  and  P.  contorta 
miirraj/ana.  Of  these,  P.  flexiUs  belongs  to  the  white  pines  and  the  others 
to  the  so-called  pitch  pines,  and  of  these  the  last,  or  P.  contorta  murrayana, 
is  by  far  the  most  abundant. 

I  have  shown  this  cone  to  a  number  of  botanists  familiar  with  the 
present  ilora,  and  there  seems  to  be  much  diversity  of  opinion  as  to  its 
probable  relationship.  Mr.  F.  V.  Coville,  botanist  of  the  Department  of 
Agriculture,  inclines  to  regard  it  as  allied  to  an  immature  cone  of  P.  scojm- 
lorum,  but  a  careful  comparison  fails  to  sustain  this  view.  Mr.  George  B. 
Sudworth,  dendrologist  of  the  Department  of  Agriculture,  regards  it  as 
most  closely  allied  to  P.  contorta  murrayana,  the  lodge-pole  pine,  and  I  have 
so  considered  it.  It  is  of  approximately  the  same  shape  as  mature  cones  of 
this  species,  but  is  longer  and  rather  narrower.  It  is  not  improbable,  as 
suggested  by  Mr.  Sudworth,  that  it  represents  a  form  which  was  the  imme- 
diate ancestor  of  P.  contorta  murrayana,  and  I  have  given  it  the  tentative 
name  of  premurrayana. 

Habitat:  East  of  the  Yellowstone  Lake,  Yellowstone  National  Park. 
Collected  by  members  of  the  Yellowstone  National  Park  division  of  the 
United  States  Geological  Survey. 

Pinus  sp. 

Cone  lanceolate?,  about  16  mm.  in  diameter,  length  of  part  preserved 
18   mm.;    scales  5   rows  in  part  preserved,  probably  about   10  or  12   in 


FOSSIL  FLORA.  679 

whole  cone,  approxinuitoly  square  (or,  better,  rhomboidal),  5  inm.  in  each 
direction;  each  scale  marked  by  a  distinct  umbo,  and  with  a  prominent 
ridge  along  the  lower  pai-t. 

The  specimen  described  is  also  the  only  one  observed.  It  is  possible 
that  it  may  be  the  same  as  P.  gracilistrohus,  as  it  comes  from  the  same  beds, 
but  it  is  nearly  twice  the  size,  and  differs  sliglitly  in  the  character  of  the 
scales  and  their  markings. 

Neither  the  base  nor  the  apex  is  preserved,  and  it  is  therefore  impos- 
sible to  know  the  length,  but  there  is  a  slight  indication  that  the  part 
preserved  is  near  the  upper  end,  as  it  is  slightly  narrowed.  This  may, 
however,  be  due  to  the  poor  state  of  preservation. 

As  stated  under  P.  gracilistrohus,  it  is  hardly  worth  while  to  attempt 
working  out  affinities  with  such  imperfect  material. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  7, 
"Castanea  bed;"  collected  by  Lester  F.  Ward  and  F.  H.  Knowlton,  August 
16-20,  1887. 

PiNUS    MACROLKPIS   n.  Sp. 
PI.  LXXX,  fig.  11. 

Scales  thick,  spatulate,  rounded  above,  slender  below,  with  a  raised 
margin  or  rim. 

The  mere  fragment  figured  represents  all  that  was  found  of  this  species. 
It  consists  of  portions  of  9  scales,  arranged  in  4  spiral  rows.  They  are 
broadly  spatulate,  being  rounded  above  and  narrow  below.  The  largest 
one  is  13  mm.  in  length,  6  mm.  broad  in  the  upper  portion,  and  about  3  mm. 
in  the  lower  portion.     The  scales  were  thick  and  have  a  strong  raised  rim. 

There  is  every  evidence  that  this  was  a  large  cone,  but  it  is  so  frag- 
mentary that  nothing  can  be  made  out  but  the  few  scales.  It  is  useless  to 
attempt  to  work  out  affinities,  except  that  it  was  probably  a  white  pine. 

Habitat:  Cliff  west  of  Fossil  Forest  Ridge,  Yellowstone  National  Park; 
collected  by  Lester  F.  Ward  and  F.  H.  Knowlton,  August  15,  1887. 

PiNUS    WARDII   n.  sp. 

Leaves  linear,  long,  apparently  in  twos,  ribbed,  not  terete. 
There  are  a  considerable  number  of  fragmentary  specimens  that  seem 
in  all  probability  to  belong  to  this  genus.     They  are  slender,  needle-like 


680  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

leaves,  about  1  mm.  broad  and  at  least  8  cm.  in  length.  They  appear  to 
have  been  ribbed,  or  at  least  not  terete  in  cross  section.  In  no  case  has  the 
point  or  base  of  the  leaves  been  observed,  but  from  the  fact  that  two  leaves 
seem  to  be  found  side  by  side,  it  seems  quite  probable  that  they  were 
arranged  in  twos,  as  in  the  living  Pinus  edtilis  Engel.,  P.  contorta  Dough,  etc. 

These  leaves  have  a  more  or  less  close  resemblance  to  certain  described 
species,  but  they  are  too  indistinct  and  poorly  characterized  to  make  any 
comparison  valuable. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  liTational  Park,  bed  No.  4, 
"Aralia  bed;"  altitude  about  8,175  feet;  collected  by  Lester  F.  Ward  and 
F.  H.  Knowlton,  August  20,  1887. 

Pinus  iddingsi  n.  sp. 
PI.  LXXXII,  figs.  S,  9. 

Leaves  linear,  very  long,  teretish,  ribbed,  in  bundles  of  three,  sheath 
obscure,  but  apparently  short. 

The  collection  contains  a  number  of  needle-shaped  leaves  that  without 
doubt  belong  to  Pinus.  They  are  about  2  mm.  broad  and  at  least  13  cm. 
long,  but  none  are  preserved  entire.  They  appear  to  be  associated  m  threes, 
and  in  one  case  (see  fig.  8)  the  upper  portion  of  a  sheath  is  preserved  with 
three  leaves  arising  out  of  it.  As  near  as  can  be  made  out,  the  leaves  are 
round  on  one  side  and  flat  and  channeled  on  the  other. 

I  have  named  this  species  in  honor  of  Prof  Joseph  P.  Iddings,  the 
collector. 

Habitat:  Andesitic  breccia  near  gulch  northwest  of  peak  west  of  Dun- 
raven;  collected  by  Joseph  P.  Iddings,  September  12,  1883. 

Taxites  olkiki  Heer. 
PI.  LXXXII,  figs.  1,4,  5. 

Several  specimens  of  this  fine  species  were  found.  They  agree  closely 
with  the  figures  given  by  Heer^  of  specimens  from  Atanekerdluk,  Greenland. 

Habitat:  Walls  of  the  canyon  of  Yellowstone  River  above  mouth  of 
Hellroaring  Creek,  Yellowstone  National  Park;  collected  by  W^alter  Harvey 
Weed,  October  13,  1887.     (Field  No.,  2961.) 


'Fl.  Fos8.  Arct.,  Vol.  I,  p.  95,  PI.  I,  figs.  21-24c. 


FOSSIL  FLORA.  681 

Sequoia  couttsi/j:  Hoer. 

The  material  which  I  incline  to  refer  to  this  species  was  found  at  only 
one  locality  within  the  Park,  namely,  the  northeast  side  of  Crescent  Hill. 
It  was  abundant  and  fairly  well  preserved.  It  consists  of  masses  of  slender 
branches  with  short  acute  appressed  leaves,  in  some  cases  with  recurving 
or  at  least  spreading-  tips.  In  a  number  of  cases  the  male  aments  were  pre- 
served. The}-  are  on  short,  slender  branches  covered  with  short  scales. 
The  aments  are  made  up  of  few  small,  irregular  scales. 

There  is  undoubtedly  much  confusion  in  regard  to  this  species.  Ac- 
cording to  Gardner,'  much  of  the  material  referred  to  by  Heer  and  others, 
from  Greenland  especially,  should  be  relegated  to  another  species,  which 
he  proposed  to  call  S.  whijmperi.  Gardner  is  also  of  the  opinion  that  por- 
tions of  the  foliage  have  by  various  authors  been  separated  as  Glyptostrohus 
ungeri.  These,  as  he  points  out,  are  usually  associated  with  Sequoia 
cones,  and  are  "never  accompanied  by  any  trace  of  the  persistent  and  very 
distinct  cones  of  Glyptostrobus."  I  believe  this  to  be  true,  and  conse- 
quently I  would  refer  to  Sequoia  couttsice  the  numerous  specimens  figured 
by  Lesquereux  as  Glyptostrohus  tmgeri,^  from  the  Green  River  group  of 
Florissant,  Colorado.  I  am  also  of  the  opinion  that  the  specimens  from  the 
Fort  Union  group,  at  the  mouth  of  the  Yellowstone,  described  by  Newberry^ 
under  the  name  of  Glyptostrobus  europmis  Brongt.,  should  be  placed  under 
Sequoia  couttsice.  I  have  never  seen  any  of  these  specimens,  however,  and 
base  tliis  conclusion  on  the  figures.  I  have  seen  a  number  of  specimens 
from  near  the  same  place,  collected  in  later  years,  and  they  seem  to  bear  out 
this  conclusion.  Some  of  the  luaterial  from  the  so-called  Laramie  of  Canada 
also  appears  to  be  properly  referable  to  this  species.  The  whole  subject 
needs  thorough  revision,  with  specimens  at  hand  from  all  localities,  and 
until  this  can  be  had  no  determinations  can  be  regarded  as  final. 

Habitat:  Northeast  side  of  Crescent  Hill,  opposite  small  pond,  Yellow- 
stone National  Park;  collected  by  F.  H.  Knowlton,  August  2,  1888. 


'  Monog.  Brit.  Eoc.  Fl.,  Vol.  II,  Pt.  I,  GymnospermiP,  p.  39. 

2  Cret.  and  Tert.  Fl.,  p.  139,  PI.  XXII,  figs.  l-6o. 

3  See  Cret.  ami  Tert.,  PI.,  XI,  figs.  6-8. 


682  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Sequoia  langsdorfii  (Brongt.)  Heer. 

PI.  LXXXII,  tig.  2. 

Sequoia  langsdorfii  (Brongt.)  Heer.:  Fl.  Tert.  Helv.,  Vol.  I,  p.  54,  PL  XX,  fig.  2;  PL 
XXI,  fig.  i. 

This  is  by  far  the  most  abundant  and  widely  distributed  conifer  found 
in  the  Yellowstone  National  Park,  with  the  possible  exception  of  Sequoia 
magnifica,  known  only  from  the  internal  structure.  It  occurs  in  many  places 
and  in  a  variety  of  forms — that  is  to  say,  the  branchlets  and  leaves  are  of 
various  sizes,  showing  that  they  have  come  from  many  individuals  and 
from  different  parts  of  the  tree.  They  are  not  of  the  same  size  and  char- 
acter as  specimens  from  the  Fort  Union  group  near  the  mouth  of  the  Yel- 
lowstone,^ being  rather  smaller  and  not  so  spreading,  but  they  are  very 
much  like  the  typical  leaves  figured  by  Heer^  from  Greenland. 

In  all  cases,  however,  the  attachment  of  the  leaves  appears  to  be 
characteristic  of  this  species.  In  one  exceptional  case  tlie  cellular  structure 
of  the  leaf  could  be  made  out.  This  agreed  perfectly  with  one  given  by 
Heer  (loc.  cit.,  fig.  21). 

In  one  or  two  cases  male  aments  were  observed  which  much  resemble 
those  figured  by  Heer  (loc.  cit.,  fig.  19). 

Habitat:  Fossil  Forest  Ridge,  beds  Nos.  4,  6,  and  7;  collected  by 
Lester  F.  Ward  and  F.  H.  Knowltou,  August  16-20,  1887.  Clift^  west  of 
Fossil  Forest  Ridge,  altitude  about  7,900  feet;  collected  by  Lester  F. 
Ward  and  F.  H.  Knowlton,  August  15,  18s7.  East  bank  of  Lamar  River, 
between  Cache  and  Calfee  creeks;  collected  by  F.  H.  Knowlton,  August  21, 
1888.  Southeast  side  of  hill  above  Lost  Creek,  bed  No.  1;  collected  by 
F.  H.  Knowlton,  August  9,  1888.  Yancey  fossil  trees;  collected  by  F.  H. 
Knowlton,  August,  1888.  South  end"  of  Crescent  Hill,  about  300  feet 
above  main  wagon  road,  bed  6  feet  below  "Piatanus  bed;"  collected  by 
F.  H.  Knowlton,  August  9,  1888.  Northeast  side  of  Crescent  Hill,  opposite 
pond;  collected  by  F.  H.  Knowlton,  August  2,  1888.  Yellowstone  below 
mouth  of  Elk  Creek,  bottom  of  bluff;  collected  by  F.  H.  Knowlton,  August 
29,  1888.     Also  obtained  by  Mr.  Arnold  Hague  (September  4,  1897)  from 

'Cf.  Newberry:  111.  Cret.  .ind  Tert.  Fl.,  PI.  XI,  fig.  4. 
:F1.  Foss.  Arct.,  Vol.  I,  PI.  II,  figs.  2-22. 


FOSSIL  FLORA.  683 

the  south  side  of  Rtiiikiiigwater  Valley,  at  a  high  bluff  east  of  the  mouth 
of  Crag  Creek,  Wyoming. 

Sequoia,  cones  of. 

_  PI.  LXXXI,  fig.  8;  PI,  LXXXII,  figs.  6,  7. 

.The  specimens  figui'ed  are  fairly  representative  of  these  organisms. 
They  are  quite  fragmentary,  yet  appear  to  be  cones.  They  are  found  in 
the  same  beds  with  Sequoia  langsdorfil,  but  not  in  actual  connection  with 
that  species,  and  I  have  preferred  to  keep  them  distinct,  at  least  for  the 
present. 

Habitat:  Fossil  Foi-est,  beds  Nos.  5  and  6;  collected  by  Lester  F. 
Ward  and  F.  H.  Kuowlton,  August,  1887. 

TYPHACE^. 

PhRAGMITES?    LATISSIMA    n.    Sp. 
PI.  LXXXIII,  fig.  5. 

Leaf  very  broad ;  stri?e  fine,  close  together. 

The  fragment  iigured  represents  all  that  has  been  collected  of  this  form. 
It  is,  of  course,  quite  insufficient  for  proper  diagnosis,  yet  it  seems  to  be 
different  from  anything  hitherto  described  from  that  region.  It  is  certainly 
quite  unlike  anything  found  in  the  Yellowstone  National  Park. 

It  must  have  been  a  very  large  leaf,  for  the  fragment  is  over  3  cm. 
broad,  and  it  was  probably  a  thick  leaf.  The  stri?e  are  very  fine,  straight, 
and  close  together.  It  differs  in  size  and  fineness  of  stride  from  P.  alaskana, 
to  which  it  seems  to  be  most  nearly  related. 

I  have  given  it  a  new  name  with  great  reluctance,  for  it  is  too  frag- 
mentary to  found  a  new  species  on,  but  for  the  present  it  va^j  remain  as 
above. 

Habitat:  Northeast  side  of  Crescent  Hill,  Yellowstone  National  Pai'k; 
collected  by  F.  H.  Knowlton  and  G.  E.  Culver,  August,  1888. 

SPARGANIACEiE. 

Sparganium  stygium  Heer. 
Sparganium  stygium  Heer.    Of.  Ward :  Types  of  the  Laramie  Fl.,  p.  18,  PI.  Ill,  figs.  6,  7. 
These  specimens  do  not  agree  in  all  particulars  either  with  those  figured 


684  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

by  Professor  Ward  or  with  the  tj^pes  as  shown  by  Heer,     They  are  quite 
obscure,  but  in  all  probability  they  are  identical  with  Heer's  form. 

Habitat :  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  Yellowstone  National  Park ;  collected  by  F.  H.  Knowlton,  August, 
1888. 

CYPERACEJl. 

Cyperacites  angustior  (A1.  Br.)  Schimper. 

Cyperacites  angustior  (Al.  Br.)  Scliimp. :  PaL  veg.  VoL  II,  p.  414, 1870. 
Cyperites  angustior  AL  Br.  Lesquereux:   Aim.  Rept.  U,  S.  GeoL  aud  Geog.  Surv.  Terr., 
1872  (1873),  p.  403. 

This  species  was  identified  by  Lesquereux,  but  the  material  can  not 
now  be  found. 

Habitat:  "Elk  Creek,  near  Yellowstone  River;  collected  by  A.  C. 
Peale,  Joseph  Savage,  and  0.  C.  Sloane." 

Cyperacites  oiganteus  n.  sp. 
PI.  LXXXII,  flg.  10. 

Leaves  large,  thick,  with  strong  midvein  and  numerous  close  nerves. 

This  species,  although  fragmentary,  is  represented  by  several  leaves 
and  stems.  The  largest  is  1 8  cm.  in  leng-th  and  about  7  mm.  in  width.  It 
has  a  well-defined  midnerve  or  vein  and  numerous  close  veins.  It  was 
evidently  of  very  firm  texture. 

Habitat :  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  base  of  bluft';  collected  by  F.  H.  Knowlton,  August,  1888 

Cyperacites"?  sp. 
PI.  LXXXIII.  flg.  i. 

This  fragment  is  all  of  this  species,  whatever  it  may  be,  that  has  thus  far 
been  found.  It  was  at  least  2.5  cm  broad  and  had  a  well-marked  keel.  The 
veins  are  strong,  about  1  mm.  apart,  with  a  fine  intermediate  vein.  There  is 
altogether  too  little  of  it  to  venture  a  specific  description  or  determination. 

Habitat:  CHflf  west  of  Fossil  Forest  Ridge;  collected  by  Ward  and 
Knowlton,  August  15,  .1887. 


FOSSIL  FLORA.  685 

Cypekacites?  sp. 
PI.  LXXXIII,  fig.  6. 

Tlie  fra<i-nieiit  figured  is  the  only  specimen  of  this  kind  in  the  collec- 
tions, and  it  is  too  imperfect  to  be  of  much  value.  It  is  about  3  mm.  broad, 
and  appears  to  be  two-ribbed — that  is,  two  of  the  ribs  are  slightly  stronger 
than  the  others.  The  fossil  is  rather  faint,  but  there  seems  to  be  only  one 
slender  rib  between  the  strong  ones. 

With  so  small  a  fragment  it  is  impossible  to  be  certain  even  of  the 
generic  reference,  but  in  this  respect  it  seems  to  agree  with  forms  that  have 
been  referred  to  Cyperacites.  It  is  left  for  future  material  to  determine  its 
status. 

Habitat:  Northeast  side  of  Crescent  Hill,  Yellowstone  National  Park; 
collected  by  F.  H.  Knowltou  and  G.  E.  Culver,  August,  1888. 

SMlLACEiE. 

Smilax  lamarensis  n.  sp. 
PL  CXXI,  figs.  3, 4. 

Leaves  large,  of  firm  texture,  ovate  or  ovate-oblong,  rounded  truncate 
at  base,  abruptly  and  obtusely  acuminate  at  apex,  margin  entire;  3-nerved 
or  obscurely  5-nerved;  petiole  splitting  into  3  equal  branches,  the  middle 
of  which  passes  straight  to  the  apex,  the  others  bending  out  to  half  the 
distance  between  midrib  and  margin,  then  curving  toward  and  entering 
the  tip;  the  lateral  strong  nerves  branch  on  the  outside,  beginning  first  at 
the  base  of  the  blade,  this  branch  sometimes  reaching  up  to  or  near  the 
apex  or  becoming  lost  near  the  middle;  sometimes  there  are  lateral  strong 
nerves  with  5  or  6  branches  on  the  outside,  all  of  which  unite  in  broad 
loops  to  produce  a  false  fifth  nerve. 

This  species  is  represented  by  several  large,  finely  preserved  examples. 
The  largest,  represented  in  fig.  4,  was  9  cm.  broad  and  at  least  14  cm.  in 
length,  and  the  smallest  (see  fig.  3)  about  4  cm.  broad  and  probably 
about  8  cm.  in  length. 

In  outline  the  leaves  are  broadly  ovate  or  ovate-oblong,  with  a  rounded 
truncate  or  cordate  base.     The  apex  in  some  cases  appears  to  be  long  and 


686  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

rather  obtusely  acuminate,  in  other  cases  quite  abruptly  aud  obtusely 
acuminate. 

The  nervation  is  strongly  marked.  The  petiole  splits  at  the  very  base 
of  the  leaf,  almost  outside  of  the  blade,  into  three  equal  divisions,  one  of 
which,  the  middle  one,  answering  to  the  midrib,  is  straight  and  ends  in  the 
apex.  The  others  arch  out  regularly  and  pass  around  and  enter  the  apex 
also.  Each  lateral  strong  nerve  or  rib  branches  on  the  outside,  the  lowest 
branch,  which  originates  just  inside  the  lower  margin  of  the  blade,  sometimes 
passing  up  and  entei'ing  the  apex  with  the  other,  at  other  times  being  lost 
below  the  middle  of  the  blade.  In  still  other  instances  there  are  5  or 
6  branches  in  the  outside  of  the  lateral  ribs  which  join  by  a  broad  loop, 
forming  a  false  nerve.  In  all  cases  this  outside  interrupted  nerve  is  much 
lighter  than  the  others. 

Smilax  appears  to  be  rarely  found  fossil  in  North  America,  as  only  5 
species  have  been  detected.  Of  these,  3  are  from  the  Dakota  group, 
and  1  each  from  the  Laramie  and  Miocene.  None  of  them  is  at  all  closely 
related  to  the  one  under  discussion. 

Smilax  lamarensis  seems  to  be  closely  related  to  a  number  of  living 
forms.  Thus  the  smaller  rounded  leaves  are  quite  like  S.  rotimdifoUa  L., 
both  in  shape  and  nervation,  while  the  larger  forms  are  hardly  to  be  sep- 
arated from  S.  pseudo-china  L.  It  is  certainly  closer  to  living  American 
forms  than  any  heretofore  described  from  this  country. 

Habitat:  East  bank  of  Lamar  River,  between  Cache  and  Calfee  creeks; 
collected  by  F.  H.  Knowlton  and  G.  E.  Culver,  August,  1888.  Fossil  Forest 
Ridge,  bed  No.  6,  "Platanus  bed,"  1  large  specimen;  collected  by  Lester 
F.  Ward  and  F.  H.  Knowlton,  August,  1887. 

MUSACEiE. 

MUSOPHYLLUM  COMPJLICATDM  Lx. 
PL  LXXXIII,  fig.  1. 
Musophyllum  compUoatum  Lx. :  Tert.  Fl.,  p.  9G,  PL  XV,  fig.s.  1-6. 

This  species  was  described  by  Lesquereux  from  a  "shale  over  a  thin 
bed  of  coal,  8  miles  southeast  of  Green  River  Station,  Wyoming,"  in  what 
he  at  first  regarded  as  the  Washaki  group,  but  which  he  later  ^  decided  was 


1  Cret.  aud  Tert.  Fl.,  p.  143. 


FOSSIL  FLOKA.  687 

tilt;  triif  Ciivc'ii  River  group.  This  lociility  has  not  since  been  visited,  and 
in  tact  can  not  now  be  satisfactorily  located.  It  is  more  than  probable, 
however,  tliat  the  former  determination  of  horizon  is  correct. 

So  f;ir  as  1  now  know,  this  is  the  second  time  this  species  has  ever  been 
found.  It  is  rej)ri'sented  by  5  or  6  fairly  well  preserved  specimens,  which 
agree  })erfectly  with  Lesquereux's  speciraeivs  and  figures. 

On  one  of  the  specimens  there  are  a  number  of  thick  stems  or  stipes. 
They  are  longitudinall}'  striate  as  described  by  Lesquereu.\,  and  bear  only 
fragments  of  the  leaves  preserved.  In  the  specimen  figured  we  have  a 
narrow  leaf  preserved  almost  entirely.  It  is  about  5  cm.  broad  and  7  cm. 
long,  as  preserved,  with  perfectly  entire  margins.  In  still  another  specimen 
the  stipe,  with  portions  of  the  lamina  attached,  is  fully  20  cm.  long.  There 
is  no  evidence  from  these  specimens  of  the  leaves  having  been  as  broad  as 
described  in  some  of  the  original  specimens,  but  Lesquereux  also  speaks  of 
narrow-leaved  forms. 

Habitat:  Northeast  side  of  Crescent  Hill,  opposite  small  pond,  Yellow- 
stone National  Park;  collected  by  F.  H.  Knowlton,  August  2, 1888. 

JUGLANDACEJl. 

JUGLANS    CALIFOENIEA  Lx. 

Juglans  californica  Lx. :  Foss.  Fl.  Aurif.  Grav.  Deposits,  Mem.  Mus.  Comp.  Zool.,  Vol. 
VI,  No.  2,  1878,  p.  35,  PL  IX,  fig.  14  ;  PL  X,  figs.  2,  3. 

There  are  2  specimens  which  I  refer  to  this  species.  They  are  of 
the  same  size  and  nervation  as  the  leaf  shown  in  fig.  2,  PI.  X,  of  Lesquereux's 
paper. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  6,  "Platanus  bed;"  collected  by 
Ward  and  Knowlton,  August  19,1 887.  East  bank  of  Lamar  River,  between 
Cache  and  Calfee  creeks;  collected  by  F.  H.  Knowlton  and  G.  E.  Culver, 
August  21,  1888. 

Juglans  rugosa  Lx. 

Juglaitx  rugosa  Lx.:  Of.  Tert.  Fl.,  p.  286,  PI.  LV,  tigs.  1-9. 

The  collections  contain  a  number  of  very  perfectly  preserved  specimens 
that  undoubtedly  belong  to  this  species.  Besides  these  there  are  a  number 
of  fragments  that  probably  belong  to  it. 

Habitat:  Fossil  Forest  Ridge,  beds  Nos.  3,  5,  6,  7;  The   Thunderer; 


688  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Hill  above  Lost  Creek,  bed  No.  4;  Crescent  Hill,  6  feet  below  Platanus 
bed;  Yellowstone  River  nearly  opposite  Hellroaring  Creek;  collected  by 
Ward  and  Knowlton,  1887,  1888. 

JUGLANS    SCHIMPERI  Lx. 

Jiiglans  schimperi  Lx. :  Tert.  Fl.,  p.  287,  PI.  LVI,  flgs.  5-10. 

The  collection  contains  a  number  of  well-preserved  examples  that 
seem  without  doubt  to  belong  to  this  species.  The  type  is  described  by 
Lesquereux  as  having  the  mai-gins  slightly  undulate.  The  Park  specimens 
are  slightly  undulate,  and  also  very  slightly  toothed.  The  nervation  is 
absolutely  the  same  in  both. 

Habitat:  Andesitic  breccia  near  gulch  northwest  of  peak  west  of 
Dunraven;  collected  by  Joseph  P.  Iddings,  September  12,  1883. 

JUGLANS    LAURIFOLIA    U.    sp. 
PI.  LXXXIII,  ligs.  2,  3. 

Leaves  large,  membranaceous,  lanceolate  or  ovate-lanceolate,  slightly 
unequal-sided,  narrowed  to  a  wedge-shaped  base  and  rounded  to  an 
acuminate  apex,  margins  remotely  and  slightly  denticulate;  midrib  thick 
below,  becoming  much  thinner  in  the  upper  part;  secondaries  about  10 
pairs,  thin,  alternate,  emerging  at  an  angle  of  45°  or  50°,  camptodrome, 
much  curving,  ascending  near  the  margin  for  some  distance,  where  they 
arch  by  numerous  loops;  intermediate  secondaries  occasional;  nervilles 
very  irregular,  much  branched;  finer  nervation  forming  irregularly  quad- 
rangular areolae. 

This  species  is  represented  by  a  number  of  well-preserved  leaves. 
They  are  from  9  to  13  cm.  long  and  3  to  5  cm.  wide,  and  are  somewhat 
unequal-sided,  the  difference  in  the  width  of  the  sides  being  about  4  mm. 
This  species  is  marked  by  its  large  size,  remotely  denticulate  margin,  and 
strong  nervation. 

Among  fossil  species,  Juglans  laurifolia  is  somewhat  related  to 
/.  egregia  Lx.,'  from  the  Auriferous  gravels  of  California.  The  leaves  of 
the  latter  species  differ,  however,  in  being  obovate-lauceolate,  with  the  broad- 
est part  above  the  middle,  and  in  having  quite  numerous,  fine,  shai-p  teeth. 

'  Mem.  Mu8.  Comp.  Zool.,  Vol.  VI,  p.  36,  PI.  IX,  fig.  12. 


FOSSIL  FLORA.  689 

Till-  lUM-vation   is  soincwliat  similar,  oxcppt  tliat  tlie  sccoiularies  are  more 
miim'rous. 

The  relation  lietweeu  ./.  laurifolia  and  J.  (Jenticaluta  Heei-,  from  the 
Green  River'  oToiip,  Carbon,  Wyoming,  etc.,  while  apparent,  is  much  more 
remote  than  in  the  case  of  the  California  .s})ecies.  This  species  has  very 
uniMinal-sided  leaves,  with  large  and  more  numerous  teeth  and  more 
numerous  arched  secondaries. 

Habitat:  Hill  above  Yanceys  and  near  the  ujmght  fos.sil  trees;  col- 
lected by  F.  H.  Knowlton,  August  28,  1888.  Also  found  on  southern  spur 
of  Chaos  Mountain,  altitude  10,100  feet;  collected  by  F.  P.  Kino-  for 
Arnold  Hague,  August  11,  1897. 

JUGLANS    CRESCENTIA    U.  sp. 
PI.  LXXXIV,  flg.  8. 

Leaflets  large,  of  firm  texture,  lanceolate,  narrowing  to  a  long  acumi- 
nate apex,  truncate  and  slightly  unequal-sided  at  base;  margin  perfectly 
entire,  slightly  undulate;  midrili  thin,  straight;  secondaries  1.5  or  18 
])airs,  alternate,  at  an  angle  of  35°  to  45°,  camptodrome,  forking  below 
tile  margin  and  joined  to  the  one  next  above,  forming  a  series  of  strono- 
bows;  intermediate  secondaries  frequent,  about  midway  between  two  sec- 
ondaries, thin  and  soon  vanishing  or  rarely  passhig  to  the  loop  made  by  the 
secondaries ;  a  series  of  small  loops  are  produced  by  outside  branches  from 
the  large  bows  which  nearly  or  quite  reach  the  margin;  finer  nervation 
dividing  the  space  between  the  secondaries  and  intermediate  secondaries  by 
large  quadrangular  areolation. 

This  fine  species  is  represented  by  a  number  of  beautifully  preserved 
specimens.  The  best  is  the  one  figured,  which  is  20  cm.  in  length  and 
nearly  4.5  cm.  in  width.  As  stated  in  the  diagnosis,  it  is  truncate  and 
slightly  unequal-sided  at  the  base  and  long  acuminate  at  the  apex.  The 
margin  is  .slightly  undulate,  but  not  otherwise  cut  or  serrated.  The  second- 
aries are  numerous,  about  16  or  17  pairs,  and  strictly  alternate.  They 
fork  at  half  or  two-thirds  of  their  length  from  the- midrib  and,  uniting 
with  the  one  next  above,  form  a  series  of  broad,  strong  loops  well  inside  the 
margin.  The  finer  nervation  is  very  perfectly  preserved,  forming  large 
but  quite  regularly  quadrangular  areola?. 


1  Tert.  Fl.,  p.  289,  PI.  LVIII.  Us.  1. 
MON  XXXII,  PT  II 44 


690  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Amono-  described  forms  this  has  some  resemljhiuce  in  shape  to 
J.  scUmperi  Lx./  from  the  Green  River  group  of  CoLirado,  but  differs  mark- 
edly in  tlie  forking  of  the  secondaries.  It  is  undoubtedly  very  close  to 
J.  acuminata  Heer,^  which  in  turn  is  hardly  to  be  distinguished  from  the 
J.  rxgosa  of  Lesquereux.  Additional  material  of  all  these  will  be  necessary 
to  settle  the  status  of  each. 

Habitat:  Northeast  side  of  Crescent  Hill;  collected  by  F.  H.  Knowl- 
ton  and  G.  E.  Culver,  August  2,  1888.  Fossil  Forest,  bed  No.  6;  collected 
by  Ward  and  Knowltou  August,  1887. 

HicoRiA  ANTiQUORUM  (Newby.)  Kn. 

Eicoria  antiquorum  (Newby.)  Ku.:  Bull.  U.  S.  Geol.  Surv.  No.  152,  p.  117,  1898. 
Garya  antiquorum  Newby.:  Later  Extiuct  Floras,  p.  72;  111.  Cret.  aud  Tert.  Plauts, 
PI.  XXIII,  figs.  1-1.     Lesquereux :  Tert.  Fl.,  p.  289,  PI.  LYII,  figs.  1-5. 

The  collection  contains  a  number  of  somewhat  fragmentary  specimens, 
but  the  characteristic  teeth  and  nervation  suffice  to  enable  their  certain 
reference  to  this  species. 

Habitat:  Fossil  Forest  Ridge,  bed  Ko.  5,  "Platanus  bed;"  collected  by 
Ward  and  Knowlton,  August,  1887. 

HiCORIA    CRESCENTIA    11.  sp. 
PI.  LXXXIY,  fig.  7. 

Leaflet  thick  and  firm,  elliptical-lanceolate,  injequilateral ;  rather  long 
wedge-shaped  at  base  and  apparently  narrowed  above  to  an  acuminate 
apex;  margin  serrate,  teeth  small,  sharp;  midrib  rather  thick,  straight; 
secondaries  about  15  pairs,  alternate,  irregular,  at  obtuse  angles,  arching 
upward,  rarely  forked,  craspedodrome,  or  subcraspedodrome,  either  arching 
near  the  margin  aud  sending  branches  to  the  teeth,  or  dividing  and  sending 
weaker  terminations  into  the  teeth;  intermediate  secondaries  occasional, 
short,  and  soon  disappearing;  nervilles  numerous,  mainly  percurrent,  approxi- 
mately at  right  angles  to  the  secondaries;  finer  nervation  forming  rather 
large  quadrangular  areolae. 

The  specimen  figured  is  the  only  one  referred  to  this  species,  and 
unfortunately  it  lacks  both  base  and  apex.     It  is  now  about  7  cm.  long  and 

'Tert.  Fl.,  p.  287,  PI.  LVI,  tigs.  5-10. 
=  F1.  Tert.  Helv.,  Vol.  Ill,  PI.  CXXVIII. 


FOSSIL  FLO  HA.  691 

2.8  cm.  hniiid.  When  I'litirc,  it  nnist  have  been  nearly  or  quite  Id  cm. 
in  leujith. 

Tliis.specie.s  is  evi(h'ntly  related  to  Varija  (Hicoria)  antiqitormii  Ne\vl)v., 
ami  it  ma\'  possibK"  l»e  an  anomalous  turm  of  that  s])ecie!s.  It  appears  to 
ditVer  essentially,  however,  in  bein^'  very  much  smaller,  less  unequal-sided, 
and  in  havinji-  larf^-er  and  less  niunerous  teeth.  The  secondaries  are  much 
the  same  in  both,  except  that  they  are  more  decidedly  cam})todrome  in 
C.  imtiquoruiH. 

It  is  also  sugo-estive  of  Juglans nigella  Ung.,  as  identified  by  Ward'  from 
the  lower  Yellowstone  River. 

Habitat:  Northeast  side  of  Crescent  Hill,  ojjposite  small  pond,  at  an 
altitude  of  about  7,500  feet;  collected  Ijy  F.  H.  Knowlton  and  G.  E. 
Culver,  July  27,  1888. 

HiCOKIA    CULVEUI    n.  sp. 
PL  LXXXIII,  fig.  7. 

Leaflets  thin,  slightly  insequilateral,  rather  long  obovate,  narrowed  from 
above  the  middle  to  a  long  wedge-shaped  base,  and  upward  to  an  acuminate 
apex;  margin  toothed  frc»m  above  the  lower  third,  teeth  flat,  obtuse;  mid- 
rili  slender;  secondaries  about  10  pairs,  alternate,  irregular,  camptodrome, 
arching  upward  and  joining  by  a  broad  curve,  watli  branches  outside  enter- 
ing the  teeth;  intermediate  secondaries  occasional,  joining  the  secondary 
below;  nervilles  very  irregular,  broken;  finer  nervation  forming  irregular 
meshes. 

The  fine  specimen  figured  appears  to  be  a  terminal  leaflet,  as  it  is  only 
slightly  inaequilateral.  It  is  perfect,  except  at  the  apex  It  is  preserved 
for  8  cm.,  and  was  probably  9.5  or  10  cm.  long.  It  is  2.7  cm.  broad  at  the 
widest  point,  which  is  high  above  the  middle.  From  this  point  it  tapers 
regularly  to  the  liase  and  appears  to  jjass  rather  abruptly  to  an  acuminate 
apex. 

This  species  has  the  same  shape  and  arrangement  as  Rhus  hendirci  Lx.,- 
from  John  Day  Valley,  Oregon,  but  diff'ers  in  the  serration  of  the  margins 
and  in  the  finer  nervation.  It  seems  likely  that  Lesquereux's  species  is  a 
Hicoria  rather  than  a  Rhus. 

'Types  of  the  Laramie  Fl.,  p.  33,  PI.  XV,  fig.  1. 

=  Prot.  U.  S.  Nat.  Mus.,  Vol.  XI,  1SS8,  p.  15.  PI.  IX,  tig.  2. 


692  GEOLOGY  OF  THE  YELL0WST02^E  NATIONAL  PAIIK. 

Among  living  species  H.  culver i  appears  closer  to  H.  ovata  (old  Carya 
alba  Nutt.),  which  has,  however,  sharper  teeth  and  more  regular  nervilles. 
The  secondaries  and  their  branches  entering  the  teeth  are  much  the  same 
in  both. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek; 
collected  by  F.  H.  Knowlton  and  G.  E.  Culver,  August,  1888. 

3IYRICACE/E. 

Myrica  scottii  Lx. 
PI.  LXXXIV,  flg.  6. 
Myrica  scottii  Lx.:  Gret.  aud  Tert.  Fl.,  p.  147,  PI.  XXXII,  figs.  17,  18. 

A  single  fairly  well  preserved  leaf,  that  seems  without  question  to 
belong  to  this  species.     It  has  been  found  before  only  at  Florissant,  Colorado. 
Habitat:  Yellowstone  River,  one-half  mile  below  Elk  Creek,  at  base 
of  bluff;  collected  by  F.  H.  Kuowkou,  August,  1888 

Myrica  wardii  n.  sp. 
PI.  LXXXIV,  tig.  4. 

Leaf  of  firm  texture,  lanceolate,  long  wedge-shaped  at  base,  obtusely 
denticulate  from  some  distance  above  the  base;  midrib  thick;  secondaries 
thin,  rather  scattered,  alternate  or  subopposite,  emerging  at  an  angle  of 
about  50°,  arching  evenly  around  arid  joining  the  one  next  above  at  a  little 
distance  from  the  margin,  their  imion  forming  a  continuous  marginal  line, 
from  the  outside  of  which  small  veins  enter  the  obtuse  teeth;  nervilles  thin, 
percurrent. 

Unfortunately  the  fragment  figured  is  the  only  specimen  of  this  form 
collected.  This  is  5.5  cm.  long  and  about  12  mm.  wide.  When  entire,  it 
was  probably  10  cm.  or  12  cm.  in  length. 

This  species  resembles  more  or  less  closely  a  number  of  described 
species,  yet  undoubtedl)''  differs  from  all.  Thus,  in  the  matter  of  the  intra- 
marginal  nei've  it  resembles  31.  torrcyi  Lx.,4romtlie  Montana  and  Laramie, 
but  is  much  larger  and  has  a  g-reater  number  of  parallel  secondaries.  In 
size  and  shape  31.  wardii  is  much  closer  to  3£.  polyniorplia  Schimp.,^  from 

'Tert.  FL,  p.  129,  PI.  XVI,  figs.  3-10. 

•Cret.  auil  Tert.  Fl.,  p.  146,  PI.  XXV,  figs.  1,  2. 


FOSSIL  FLORA.  693 

F'loris.sant,  Coloriulo.  It  differs  essentially  in  having-  I'atlier  numerous 
sec'ondafies,  wliicli  jjarallel  enter  the  somewhat  shar})er  teeth.  M.  fallax 
Lx.,'  also  trom  Florissant,  is  evidently  related,  but  has  nuich  larger,  sharp 
teeth,  and  nervation  as  in  M.  poJjimorpJia  Lx. 

Hal)itat:  Fossil  Forest  Ridge,  bed  No.  5,  "Salix  bed;"  collected  by 
Ward  and  Ivnowlton,  August  19,  1SS7. 

Myrica  lamarensis  n.  sp. 
PL  LXXXIV,  fig.  .5. 

Leaf  iinu  in  texture,  narrowly  lanceolate,  narrowed  below,  apparently 
acuminate  at  apex;  margin  at  some  distance  above  the  base,  provided  with 
numerous,  small  teeth;  petiole  short;  midrib  rather  thick,  straight;  nerva- 
tion pinnate,  camptodrome,  the  secondaries  joining  and  forming  a  thin  line 
from  inside  the  border;  other  nervation  destroyed. 

The  little  leaf  has  onh'  the  lower  portion  preserved.  It  is  now  3.5  cm. 
in  length,  and  when  entire  was  probably  not  less  than  6  cm.  long.  It  is 
only  7  mm.  broad,  and  has  a  short  petiole  about  2  mm.  in  length.  The 
nervation  is  also  destroyed,  except  the  midrib  and  about  a  dozen  secon- 
daries, wdiicli  are  seen  to  be  alternate.  They  arch  and  join,  producing  a 
marginal  line  just  inside  the  margin. 

This  little  leaf  does  not  appear  to  have  any  very  close  relative  in 
this  country.  Those  approaching  ueai-est,  perhaps,  are  the  narrow  leaved 
species  so  common  at  Florissant,  Colorado,  such  as  M.  fallax  Lx.,-  and  M. 
scottii  Lx.^  They  differ  markedly,  however,  in  the  sliarpl}'  serrate  margin 
and  craspedodrome  nervation. 

Myrica  hanlisicefoUa  Ung.,  as  figm-ed  by  Heer''  from  the  Baltic  Miocene, 
is  perhaps  nearer  to  our  species.  This  has  the  narrowed  base  and  similar 
teeth,  but  differs  in  the  apex  and  in  the  nervation. 

Habitat:  East  bank  of  Lamar  River,  between  Cache  and  Calfee 
creeks;  collected  by  F.  H.  Knowlton,  August  21,  1888. 

'Op.  cit.,  p.  147,  PI.  XXXII,  figs.  11-16. 
=  Ci-et.  and  Tert.  Fl.  p.  147,  PI.  XXXII,  tigs.  11-16. 
■'Loc.  cit.  p.  147,  PI.  XXXII,  tigs.  17,  18. 
^Mioc.  Bait.  Fl.,  p.  67,  PI.  XVIII,  tig.  4. 


694        geoluctY  of  the  yellowstojne  national  pakk, 

SALICACEiE. 

POPULUS    GLANDULIFEKA    Heev. 

PI.  LXXXIV,  fig.  1. 

ropnliis  (ilanduUfera  Heer.     Lesquereiix:  Oiet.  ami  Tert.  Fl.,  p.  226,  PL  XLVIa,  flgs. 
3,  4.     Ward :  Types  of  the  Laramie  Fl.,  p.  19,  PI.  IV,  figs.  1-4. 

The  collection  contains  3  specimens  with  very  line  rounded  or  sharp 
teeth,  that  are  referred  without  hesitation  to  this  species,  as  figured  by 
Lesquereux  and  Ward,  from  the  tjqiical  Fort  Union  groxij)  of  the  lower 
Yellowstone.     The  best  of  these  is  figured. 

Habitat:  Yellowstone  River,  one-half  mile  below  tlie  mouth  of  Elk 
Creek;  collected  by  F.  H.  Knowlton,  August,  1888. 

PopULUs  SPECiosA  "Ward. 

PI.  LXXXIV,  fig.  .}. 

PopuJuH  speciosa  Ward:  Types  of  tlie  Laramie  FL,  p.  20,  PI.  V,  flgs.  4-7. 

The  Park  collection  contains  something  over  50  specimens  that  are 
referred  to  this  species.  They  are  very  perfectly  preserved,  and  the  petiole 
is  in  some  cases  8  cm.  in  length.  There  can  be  no  qiiestion  as  to  their 
correct  reference  to  the  Fort  Union  species.  I  should  also  iiicline  to  refer 
to  this  species  certain  of  the  leaves  described  as  Pojmltis  amhh/rJii/ncha  Ward 
and  P.  oxurhymlia  Ward,  from  the  same  beds.  The  very  slight  differences 
separating  these  forms  seem  hardly  to  be  worthy  of  specific  rank. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk 
Creek;   collected  by  F.  H.  Knowlton,  August,  1888. 

PopuLUS  ZADDACHi  Hecr. 

Popidus  zaddachi  Heer:   Fl.  Tert.  Helv.,  Vol.  Ill,  p.  307.     Lesijuereux:   Cret.  and 
Tert.  Fl.,  p.  158,  PI.  XXXI,  fig.  8. 

A  few  specimens  were  obtained  that  nuist  be  referred  to  this  species. 
Habitat:    Late    acid    breccia,    Pyramid    Peak;    collected    by  Arnold 
Hague,  1897. 


FOSSIL  FLOKA.  695 

PoPULUS    XANTHOLITHENSIS    11.  Sp. 
PI.  L XXXV,  figs.  1,13. 

Leaves  l;irg\%  nciirly  vumu\  in  (tutliiic,  l)ut  a  little  broader  than  long, 
truiK-ate  or  sli<ihtl}  heart-shaped  at  Viase,  rounded  above;  margin  strongly 
toothed;  teeth  in  lower  portion  simple  and  rounded,  others,  along  the  side  of 
tlu'  blade,  inclined  to  be  double-toothed — that  is,  each  large  tooth  has  one  or 
2  smaller  rounded  projections;  petiole  long,  slender;  blade  7-nerved;  cen- 
tral or  midrib  strt)ng,  straight,  pair  of  ribs  nearest  the  midrib  originating 
at  a  little  distance  above  the  base  of  the  blade,  arching  around  and  reach- 
ing the  apex  near  together,  other  2  pairs  arising  from  the  apex  of  the 
petiole  and  dividing  equally  the  remaining  portion  of  the  blade;  midrib 
with  about  3  pairs  of  secondaries  in  the  upper  part,  next  pair  of  ribs  with 
4  or  5  branches  on  the  outside,  other  ribs  with  numerous  branches  which 
anastomose,  producing  large  irregular  areas,  with  minute  branches  to  the 
teeth;  nervilles  numerous,  mainly  broken,  occasionally  percurrent;  finer 
nervation  quadrangular. 

The  2  beautiful  specimens  figured  are  the  only  ones  referred  to  this 
species.  Fig.  1,  which  lacks  the  upper  portion,  is  9.5  cm.  broad  and  7.5 
cm.  long.  It  has  the  petiole  preserved  for  5.5  cm.  Fig.  2,  which  lacks  a 
portion  of  one  side  and  a  fragment  at  the  apex,  is  8.5  cm.  in  length  and 
10  cm.  in  width.     The  petiole  is  not  preserved. 

The  relation  of  this  species  is  evidently  with  Populus  genatrix  Newby.,^ 
from  the  Lower  Yellowstone.  This  is  about  the  same  size  and  much  the 
same  shape,  except  tliat  it  is  more  prolonged  at  the  apex.  The  margin  is 
described  as  having  "rather  small,  appressed  teeth,"  while  those  of  P.  xan- 
tMiilmisis  are  larger,  sometimes  double,  and  never  appressed.  The  former 
species  was  described  by  Newberry  as  "3-nerved,"  although  the  figure 
shows  it  to  be  clearly  5-nerved.  The  present  species  is  just  as  clearly 
7-nerved.  The  midrib  and  its  branches  also  differ  markedly  in  the  two 
forms. 

This  species  has  also  some  affinity  with  certain  of  the  forms  described 
by  Professor  Ward  from  the  lower  Yellowstone,  but  the  relationship  is  not 
close. 


L.iter  Ext.  Fl.,  p.  64 ;  HI.  Cret.  and  Tert.  FI.,  PI.  XII,  tig.  1. 


696  GEOLOGY  OF  THE  YELLOWSTOiNE  NATIONAL  PARK. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;   collected  by  F.  H.  Knowlton,  August,  1888. 

PoPULUs  DAPHXOGENOiDES  Ward. 
PI.  LXXXIV,  fig.  2. 
Populus  daphnogenoides  Ward:  Types  of  the  Laramie  Fl.,  p.  20,  PL  VII,  figs.  4-6. 

Tlie  collection  contains  some  20  specimens  that  are  referred  to  this 
species.  Tliej-  have  the  same  general  character,  but  are  a  little  larger, 
with  a  more  prolonged  point  and  rather  stronger  nervation.  There  are  no 
essential  differences,  however. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Populus  balsamoides  Gopp. 

PLLXXXVI,  fig.  1. 

Populus  balsamoides  Giipp.  Lesquereux:  Cret.  and  Tert.  Fl.,  p.  248,  PI.  LY,  figs.  3-5. 

The  fragment  figured  is  the  only  specimen  of  this  species  detected. 

It  represents  the  basal  portion  of  a  medium-sized  leaf,  and  agrees  satisfac- 

toril}-  with  the  figures  of  this  species  as  given  by  Lesquereux. 

Habitat:  Cliff  west  of  Fossil  Forest  Ridge;  collected  by  Ward  and 
Knowlton,  August  15,  1887. 

Populus  *?  vivaria  n.  sp. 
PI.  LXXXVI,  fig.  2. 

Leaf  thick,  romidish,  or  broadly  elliptical  in  outline,  toothed  to  near  tlie 
base;  teeth  large,  acute;  nervation  pinnate,  camptodrome,  or  imperfectly 
craspedodrome;  secondaries  strong,  opposite  or  subopposite,  emerging  at 
various  angles,  forking  near  the  margin,  the  branches  arcliing  into  bows 
and  apparently  sending  branches  from  the  outside  to  the  teetli;  nervilles 
obscure,  but  apparently  percurrent. 

This  doubtful  species  rests  on  the  single  fragment  figured.  It  was 
apparently  about  10  cm.  long  and  7  cm.  wide.  It  has  some  resemblance  to 
certain  species  of  Populus  from  the  Fort  Union  group  of  the  lower  Yellow- 
stone, as,  for  example,  P.  f/reiviojisis  Ward,"  but  differs  in  the  branching  of 


'Types  of  the  Laramie  Fl.,  p.  23,  PI.  IX,  fig.  1. 


FOSSIL  FLOKA.  697 

tlic  lower  lar<>e  ftocondary,  and  somewhat  in  tlie  teeth.  The  nerves  are 
also  eraspedodrome  in  I'.firen-iopsis. 

It  is  really  too  tra<iiueutary  and  uncertain  for  identification,  yet  it  differs 
from  anything  else  found  in  the  collection,  and  is  simply  named  in  a  purely 
provisional  manner,  awaiting  subsecpient  collections. 

Habitat:  AVest  end  i>f  Fossil  Forest  Kidge;  collected  by  Ward  and 
Knowlton,  August  15,  1887. 

Salix  varians  Heer. 

PI.  LXXXV,  fig.  3. 

Saliv  varians  Heer:  FI.  Tert.  Helv.,  Vol.  II,  PI.  LXV,  figs.  1-3,  6-16. 

The  exami)le  figured  certainly  belongs  to  this  species.  It  is  the  same 
shape,  but  a  little  larger,  and  has  the  same  erose-dentate  margin  and  the 
same  midrib  and  general  nervation. 

Habitat:  Lamar  River,  between  Cache  and  Calfee  creeks;  collected  by 
Knowlton  and  Culver,  August  27,  1888. 

Salix  angusta  A1.  Br. 

Salix  angusta  Al.  Br.  Lesquereur:  Tert.  FL,  p.  IGS,  PI.  XXII,  figs.  4,  5;  Cret.  aud 
Tert.  FL,  pp.  157,  247,  PL  LV,  fig.  6. 

This  species,  originally  described  by  Heer  from  the  Swiss  Tertiary, 
has  been  found  by  Lesquereux  in  the  Green  River  group  at  Florissant, 
Colorado,  and  in  the  Miocene  of  Oregon.  A  number  of  doubtful  fragments 
were  reported  from  Spring  Canyon  in  the  Bozemau  coal  field,  but  they  are 
too  fragmentary  to  be  of  an}-  value. 

Habitat:  Lamar  River,  between  Cache  and  Calfee  creeks;  doubtful 
fragments;  collected  by  F.  H.  Knowlton,  August,  1888;  also  specimens 
No.  1967  of  Hague's  Park  collection. 

Saux  lavateri  Heer. 

Salix  lavateri  Heer:  FL  Tert.  Helv.,  Vol.  II,  p.  28,  PL  LXVI,  figs.  1-12;   FL  Foss. 
Alask.,  PL  II,  tig.  10.     Lesquereux:  Proc.  U.  S.  Nat.  Mus.,  Vol.  XI,  1888,  p. 35. 

Habitat:  South  end  Crescent  Hill,  bed  25  feet  above  "Platanus  bed;" 
collected  by  F.  H.  Knowlton,  August,  1888. 


698  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Salix  elongata  1  0.  Web. 
SdUx  elongata  O.  Web.     Lesquereux:  Tert.  Fl.,  p.  169,  PI.  XXII,  figs.  6,  7. 

A  sing-le  quite  well  preserved  specimen  that  seems  to  belong  to  this 
species.  The  nei'vation,  however,  is  not  well  preserved,  but  as  nearly  as 
can  he  nia;le  out  it  may  be  referred  to  this  form. 

Habitat:  Fossil  Forest,  lower  stratum.  No.  1221  of  Hag'ue's  Yellow- 
stone National  Park  collection;  collected  by  Arnold  Hague,  September 
24,  1884. 

BETULACEvE. 

Betula  iddingsi  n.  sp. 
PI.  LXXXVI,  figs.  4,  o. 

Leaves  membranaceous,  ovate,'  slightly  unequal-sided,  rather  abruptly 
rounded  to  the  base,  more  prolonged  above ;  margin  regularly  toothed  from 
near  the  base,  teeth  slightly  unequal,  a  little  hooked;  nervation  pinnate 
and  craspedodrome ;  midrib  well  marked,  straight;  secondaries  about  10 
pairs,  mainly  alternate,  occasionally  opposite,  arising  at  an  angle  of  about 
45°,  straight  or  nearly  so,  terminating  in  the  larger  teeth,  often  with  forks 
near  the  margin,  all  of  which  enter  the  other  teeth;  nervilles  obscure,  but 
apparently  percurrent  and  at  right  angles  to  the  secondaries;  finer  nerva- 
tion not  preserved. 

This  species  is  represented  b)^  3  very  perfect  leaves,  nil  of  which  are 
preserved  on  the  same  piece  of  matrix  The  most  perfect  one  figured  is 
8  cm.  in  length  and  4.5  cm.  wide,  while  the  other  is  about  8  cm.  long  and 
less  than  4  cm.  wide.  The  petiole  belonging  to  this  specimen  is  7  mm. 
in  length. 

This  species  somewhat  resembles  a  number  of  described  forms,  as,  for 
example,  Betula  stevensoni  Lx.,^  from  Carbon,  Wyoming,  from  which  it  diff'ers 
somewhat  in  shape,  numbej*  of  pairs  of  secondaries,  and  in  the  more  regularly 
serrate  margin.  Betula  eUiptica  Sap.,  as  identified  by  Lesquereux^  from 
John  Day  Valley,  Oregon,  is  perhaps  closer,  yet  this  differs  in  having  only 
6  or  7  pairs  of  secondaries  and  also  in  the  teeth.  Betula  parce-dentata 
Lx.,  from  the  same  locality,  has  the  same  kind  of  teeth,  but  diff'ers  in  size. 


'Tert.  Fl.,  p.  139,  PI.  XVHI,  figs.  1-5. 
-Cret.  and  Tert.  Fl.,  p.  242,  PI.  LI,  fig.  6. 


FOSSIL  FLORA.  699 

IVsidi's  tlu'se,  lu'ltinjiing-  to  tlie  frenus  Ik'tula,  tliero  nro  a  nuinl)er  of 
otluTS  more  or  less  resi'nil)ling  this  leaf;  e.  <■'.,  Alntts  cdrpinohlcs  Lx.,'  from 
Hridgo  Creek,  Oreg'on,  and  Celastrus  ovatus  Ward,  from  the  Fort  Union 
grou})  of  .Montana. 

Amon<?  living  species  this  appears  to  be  closest  to  Betula  Intea  Michx., 
but  even  this  is  somewliat  remote.  In  the  future  it  may  be  thought  best 
to  place  this  fossil  species  under  some  other  genus,  for  which,  no  doubt, 
reasons  mav  be  foimd,  but  for  the  jjresent  it  seems  best  to  place  it  in  Betula. 

Betula  fCfjiialis  Lx.,^froni  the  Auriferous  gravels  of  California,  is  evidently 
closelv related;  but  this  differs  in  being-  much  narrower,  more  wedge-shaped 
at  base,  and  in  having  fewer  and  smaller  teeth.  B.  prisca  Ett,  as  figured  by 
Ward'  from  the  uppermost  Fort  Union,  near  the  mouth  of  the  Yellowstone 
River,  is  similar  but  much  smaller. 

This  species  is  named  in  honor  of  Prof.  J.  P.  Iddings,  of  the  University 
of  Chicago,  who  pointed  out  the  localit}^  at  which  it  was  iirst  collected. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888.  Hill 
above  Lost  Creek,  bed  No.  2;  collected  by  F.  H.  Knowlton,  August  5,  1888. 

CoRYLUS  MACQtT.ARRYi  (Forbe.s)  Hecr. 

PI.  LXXXVI,  fig-.  3. 

Cori/his  macquarry!  (Forbes)  Heer:  Crwelt  d.  Schweiz,  p.  321,  18(15. 

The  collection  contains  a  single  well-preserved  specimen  that  is  referred 
with  some  little  hesitation  to  this  well-known  species.  It  has  the  proper 
shape,  including  the  heart-shaped  base  and  identical  nervation,  but  differs 
slightly  in  the  marginal  dentation.  In  the  typical  form  the  margin  has 
numerous  rather  small,  sharp,  upward-pointing  teeth,  while  the  one  under 
consideration  has  fewer,  rather  blunt  teeth.  It  may  not  be  the  same,  but 
rather  than  make  a  new  species  I  have  referred  it  to  C.  inacqnarnjL 

Habitat:  Fossil  Forest,  middle  stratum,  Hague's  Yellowstone  National 
Park  collection  (No.  1220);  collected  by  Arnold  Hague,  September  24, 1884. 


'Op.  cit.,  p.  243,  PI.  LI,  fig.  5. 

-Mem.  Mas.  C'omp.  Zo;!!.,  1878,  p.  2,  PI.  I,  figs.  2-4. 

^Types  of  tlie  Laramie  FL,  PI.  XIV,  fig.  2. 


700  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

FAGACEiE. 

Fagus  antipofii  Aljich. 

Fagus  antipofii  Abich.    Lesquereux :  Ann.  Eept.  U.  S.  Geol.  and  Geog.  Surv.  Terr.,  1S72 
(1873),  p.  403. 

Identified  by  Lesquereux,  but  not  since  observed. 
Habitat:   "Elk  Creek,  near  Yellowstone  River;    A.  C.  Peale,  Joseph 
Savage,  and  O.  C.  Sloane." 

Fagus  undulata  n.  sp. 

PI.  LXXXV,  figs.  4,  5. 

Leaves  small,  of  very  firm  texture;  elliptical  with  a  broadly  wedge- 
shaped  base  and  apparently  obtuse  apex;  margin  regularly  undulate- 
toothed,  the  teeth  being  regularly  rounded  and  separated  by  similarly 
rounded  sinuses;  midrib  strong,  straight;  secondaries  numerous,  opposite, 
parallel,  unbranched,  all  entenng  the  obtuse  teeth;  nervilles  ver^- numerous, 
at  right  angles  to  the  secondaries,  usually  broken  and  anastomosing, 
although  sometimes  irregularl}"  percurrent;  finer  nervation  producing 
small,  irregularly  quadrangular  areolation. 

This  tine  species  is  fortunately  represented  by  several  very  perfectly 
preserved  examples,  the  two  figured  showing  both  the  basal  and  apical  por- 
tions. They  vary  in  length  from  6  to  K)  cm.  and  in  width  from  2.75  to  4 
cm.  The  margins  are  ^•er^'  regularly  uudulate-toothed,  the  sinuses  being 
almost  an  exact  reverse  of  the  nearest  teeth.  The  wedge-shaped  base  is, 
however,  without  teeth  for  a  short  distance.  The  secondaries  are  at  an 
angle  of  about  45°.  They  are  parallel,  and  all  enter  the  obtuse  teeth.  All 
of  the  finer  nervation  is  beautifully  preserved  and  is  seen  to  be  irregularly 
quadrangular. 

This  species  does  not  approach  closely  to  any  living  species  known  to 
me.  It  is  perhaps  nearest  to  certani  forms  of  the  common  American  F. 
ferruginea  Ait,  but  the  living  form  difters  in  being  proportionately  broader, 
and  when  toothed  has  sharp  teeth,  quite  like  Castanea,  and  pointing  upward. 

Among  the  80  or  more  fossil  species  that  have  been  described  from 
various  parts  of  the  world,  there  are  several  that  our  species  more  or  less 
closely  resembles.     Of  these,  F.  dentata  Gopp.,  as  identified  by  Heer'  in  the 

'  Fl.  Foss.  Arct.,  Vol.  I,  p.  106,  PI.  X,  figs.  76, 9. 


FOSSIL  FLORA.  701 

Koceuc  beds  iit  Atancki'nlliik,  Cireenlaii<l,  perliap.s  approaclies  most  closely. 
Tlu'V  are,  however,  larger  leaves,  with  coarser,  more  acute  teeth  and  fewer 
strictl}-  alternate  secoiularies.  The  leaves  of  F.  undulata  are  quite  unlike 
the  type  specimen  of  F.  dentnta  as  described  by  Goppert'  from  the  Tertiary 
of  Schossnitz,  as  indeed  are  the  leaves  doubtfully  so  identified  by  Heer. 

The  Yellowstone  National  Park  leaves  are  also  quite  like  leaves  of 
Fufim  atstancccfolia  Ung\,  as  figured  by  Heer-  from  the  same  beds.  These 
were  afterwards  referred  by  Heer^  to  his  Castauea  unyen  on  what  seems  to 
me  to  have  been  insufficient  g-rounds.  There  is  hardly  any  difference 
between  these  and  leaves  of  F.  undulata,  except  that  the  teeth  are  a  little 
sharper.  It  is  probable  that  they  should  be  placed  together,  but  as  the 
status  of  Heer's  plants  is  somewhat  unsettled,  I  have  preferred  to  keep  them 
separated  for  the  present. 

Giippert  has  also  described  another  species,  F.  attenuata,  from  Schoss- 
nitz,  which  is  really  quite  close  to  F.  undulata.  It  is  about  the  same  size  and 
has  rounded  teeth,  but  there  is  uniformly  a  tooth  between  two  of  the  teeth 
which  are  entered  by  the  secondaries.  In  F.  undulata  every  tooth  is  entered 
by  a  secondary. 

Fagiis  antipofii  Abich,  as  figured  by  Heer,^  from  the  so-called  Miocene  of 
Alaska,  is  not  greatly  unlike  the  species  under  consideration.  It  has  the 
outline,  parallel  secondaries,  and  finer  nervation,  but  not  the  same  kind  of 
teeth.  There  are  a  number  of  other  species,  as  F.  atlantica  Uug.,  F.  feronice 
Ung.^  as  figured  by  Lesquereux"  from  Elko,  Nevada,  etc.,  that  resemble 
F.  undulata  in  one  or  more  particulars,  but  not  by  an}^  means  sufficiently 
for  specific  identity. 

But  among  all  fossil  forms,  two  of  the  leaves  described  by  Heer  as 
Castanea  ungeri,''  from  the  supposed  Miocene  of  Alaska,  are  undoubtedly 
nearest  to  the  species  under  consideration.  •  They  are  of  about  the  same 
size  and  shape,  but  have  teeth  a  little  more  acute.  The  secondaries  are 
numerous,  parallel,  and  enter  the  teeth  as  in  Fagus  undulata,  but  in  origin 

'  Tert.  Fl.  v.  ScUossuitz  in  Schlesieu,  Gorlitz,  1855,  p.  18,  PI.  V,  fig.  11. 

-  Fl.  Foss.  Arct..  Vol.  I,  p.  106,  PI.  X,  tig.  la  :  PI.  XLVI.figs.  1-3. 

^Loc.  cit.,  Vol.  11  (Fl.Foss.  Mask.),  p.32. 

^Loc.  eit.,  PL  Vll,  lig.  4. 

5  Chlor.  Prot.,  PI.  XXVil,  fig.  2. 

6Tert.  Fl.,  p.  146,  PI.  XIX,  figa.  1-3. 

'  Fl.  Foss.  Arct.,  Vol.  II  (Fl.  Foss.  Alask.),  PI.  VII,  tigs.  1, 2. 


702     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

they  are  uuifoviulj-  alternate  instead  of  opposite.  The  2  leaves  figured 
by  Heer  I  regard  as  very  doubtful.  From  their  general  facies  they  are 
much  more  likely  to  belong  to  Fagus  than  to  Castanea.  The  other  leaf 
figured  with  them^  does  not  appear  to  be  the  same,  and  is  probably  a  Cas- 
tanea, although  somewhat  anomalous.  They  are  found  associated  in  the 
same  Ijeds  Avith  2  species  of  Fagus,  from  which  they  are  hardly  to  be 
separated. 

Habitat:  Bluff  on  Yellowstone  Rivei- 1  mile  below  mouth  of  Elk  Creek, 
and  about  same  distance  above  mouth  of  Hellroaring  Creek;  collected  by 
F.  H.  Knowlton,  August  4,  1888. 

Castanea  pulchella  n.  sp. 
PI.  LXXXVl,  figs.  6-8;  PI.  LXXXVII,  figs.  1-3. 
Quercm  drymeja  Ung.     Lesqiiereiix :  Cret.  and  Tert.  Fl.,  p.  I'i5,  PI.  LIV,  fig,  i. 

Leaves  of  very  thick,  tirm  texture;  long -lanceolate  in  outline,  with 
wedge-shaped  base  and  long,  slender,  acuminate  apex;  margin  evenly  and 
regularly  toothed;  teeth  large  and  sharp,  separated  by  prominent  sinuses, 
or  more  obtuse  with  shallower  sinuses;  petiole  long,  slender;  midrib  strong, 
straight;  secondaries  very  numerous,  opposite  or  alternate,  jjarallel,  all, 
except  two  or  three  of  the  lowest,  entering  the  teeth;  nervilles  well  pre- 
served, numerous,  at  right  angles  to  the  secondaries,'  mainl)^  broken. 

This  fine  species  is  represented  by  a  very  large  sei-ies  of  specimens, 
nearly  all  in  excellent  state  of  preservation.  They  range  in  size  from  about 
8  to  20  cm.  in  length  and  from  2  to  6  cm.  in  width,  while  the  petiole  in  some 
cases  is  3.5  cm.  long  and  rather  slender.  They  are  lanceolate  in  outline, 
with  a  long  wedge-shaped  base,  which  is  without  teeth  for  some  distance, 
and  a  very  long  slender  apex  provided  with  numerous  strong  teeth.  The 
teeth  of  the  margin  are  numerous  and  regular,  in  some  cases,  as  in  fig.  2 
of  PI.  LXXXVII,  being  very  large  and  sharp,  while  in  others  the}'  are 
less  prominent.  They  are,  however,  all  sharp  and  upward  pointing.  The 
secondaries  are  numerous,  parallel,  and  entering  the  teeth.  The  finer 
nervation  is  well  preserved,  the  nervilles  being  numerous  and  mainly 
broken  in  crossing. 

It  is  with  some  hesitation  that  these  leaves  are  described  as  new  to 
science.     At  first  they  were  thought  to  be  the  same  as  the  leaves  from 


iLoi!.  cit.,Pl.  VII,tig.3. 


FOSSIL  FLORA.  703 

the  Aurit'iTous  gravi'ls  ot'  (Jalitoniiu  i-ct'erred  hy  Lescjuereux  to  ('ustanea 
unyi'ti  Ileer,'  l)ut  a  cari'tul  study  of  the  Yenowstone  National  Park  material, 
comprising  nearly  lOlt  specimens,  and  ot"  a  fine  collection  from  Inde- 
pendence Hill,  Placer  Connty,  California,  has  convinced  me  that  they  are 
distinct,  althouo'h  closely  related.  The  California  species  ditfei  in  having 
a  shorter  petiole,  in  the  wedge-shaped  base  being  destitute  of  teeth  for  a 
greater  distance,  in  having  serrate  margins  rather  than  Castanea-like  teeth, 
and  in  having  in  general  closer  secondaries.  This-  study  has  also  brought 
out  the  fact  that  Lesquereux  could  hardl}'  have  been  correct  in  identifying 
the  California  specimens  with  Castanm  tmgeri  as  figured  by  Heer-  from 
Alaska.  As  already  stated  imder  Fagus  undiilata  (p.  700),  it  is  more  than 
probable  that  2  of  the  leaves  figured  by  Heer  (loc.  cit.,  PI.  VII,  figs.  1,  2) 
should  be  restored  to  Fagus,  and  the  other  is  certainly  specificalh'  distinct 
from  the  California  leaves.  The  California  specimens,  as  stated,  differ  also 
from  the  Yellowstone  National  Park  species,  and  should  probably  be  given 
a  new  name. 

Lesquereux  identified^  as  Qnercus  iJrymeja  Uug.,  a  single  leaf  from 
Bridge  Creek,  Oregon,  that  must  certainly  be  the  same  as  Castanea  pulclidla. 
It  is,  for  exam2)le,  absolutely  indistinguishable  from  fig.  7  of  PL  LXXXYI 
and  fig.  2  of  PI.  XXXVII.  A  comparison  of  certain  of  the  European  figures 
of  Q.  dnjmeja  makes  it  more  than  probable  that  it  was  not  correctly  identified 
among  the  Bridge  Creek  material.  The  leaf  figured  by  Lesquereux  is 
referred  to  C.  pulchella,  and  Q.  drymeja  should  be  stricken  from  the  west- 
coast  flora,  at  least  so  far  as  it  depends  on  this  particular  specimen. 

It  was  at  first  thought  best  to  separate  the  small  leaves  represented  in 
fig.  7  of  PI.  LXXXVI  and  figs.  2  and  3  of  PI.  LXXXVII,  as  a  distinct 
species,  but  the  only  difference  is  one  of  size,  and  in  the  large  series  at  hand 
this  breaks  down.  All  gradations  from  the  smallest  to  the  largest  may  be 
found,  which  is  quite  in  accord  with  the  well-known  differences  in  size  of 
leaves  to  be  found  on  living  Castanea. 

Habitat:  Fossil  Forest  Ridge,  Y^ellowstone  National  Park,  bed  No.  7, 
altitude  about  7,250  feet;  collected  by  Lester  F.  Ward  and  F.  H.  Knowlton, 
August  16-20,  1887.     Y'ellowstone  River,  one-half  mile  below  mouth  of  Elk 

'Ciet.  aud  Tert.  Fl.,  j).  246,  PI.  LIT,  figs.  1,  3-7. 

-Fl.  Fuss.  Arct.,  Vol.  II  (Fl.  Foss.  Mask.),  p.  32,  PI.  VII,  figs.  1-3. 

^Cret.  aud  Tert.  FL,  p.  245,  PI.  LIV,  tig.  4. 


704     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Creek,  bluff  300  feet  above  stream;  collected  by  F.  H.  Knowlton,  August 
27,  1888.  Junction  Butte  Fossil  Forest,  altitude  about  7,-450  feet;  collected 
by  Lester  F.  Ward  and  F.  H.  Knowlton,  August  25,  1887. 

QUEECUS    GROSSIDENTATA  n.  sp. 
PL  LXXXVII,  fig.  7. 

Leaf  large,  coriaceous,  broadly  lanceolate  (base  destroyed),  apex 
acuminate;  margin  strongly  toothed,  the  teeth  sharp,  upward  pointing; 
midrib  perfectly  straight;  secondaries  about  8  or  9  j^airs,  alternate,  at 
an  angle  of  45°,  craspedodi-ome,  slightly  arching  upward,  ending  in  the 
large  teeth;  nervilles  strong,  at  right  angles  approximately  to  the  midrib, 
mainly  percurrent,  but  occasionally  forked  or  broken,  finer  nervation  not 
retained. 

Unfortunately  this  fine  species  is  re])resented  by  the  single  specimen 
figured,  and  this,  it  may  be  seen,  lacks  the  basal  portion.  The  part  retained 
is  10  cm.  long  and  4.5  cm.  wide.  It  was  probaljly  14  or  15  cm.  in  length 
when  perfect.  It  has  the  margin  strongly  toothed,  the  teeth  with  long, 
rounded  or  sharp  points,  each  of  which  is  entered  by  a  secondary. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  5;  collected  by  Ward  and 
Knowlton,  August  19,  1887. 

QuEKCus  coNsiMiLis?  Newby. 

PL  LXXXVII,  tig.  C. 

Qiiercus  consimilis  Newby.:  Proc.  U.  S.  Nat.  Mus.,  VoL  V,  p.  505,  18S2  [1883]. 
Quercus  hreicerl  Lx. :  Cret.  and  Tert.  ii'L,  p.  240,  PL  LIV,  figs.  5-8. 

This  is  only  a  fragment  of  the  base  of  a  leaf.  It  does  not  agree 
absolutely  with  the  figures  of  Lesquereux,  but  rather  than  make  it  a  new 
species  I  have  referred  it  provisionally  as  above. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  top  of  bluft';   collected  by  F.  H.  Knowlton,  August,  1888. 

Quercus?  magnifolia  n.  sp. 
PL  LXXXVIII,  fig.  1. 

Leaf  large,  of  firm  texture,  long,  broadlj'  obovate,  narrowed  to  the  base, 
rounded-obtuse    at   apex;    margin    at  base    entire,    remainder  of    margin 


FOSSIL  FLOEA.  705 

destroyed,  but  probably  toothed  or  lobed;  midrib  thick,  straig-ht;  seconda- 
ries about  18  pairs,  aheriiate,  at  various  angU^s,  curving-  upward,  apparently 
cauiptodronie;  tiner  nervation  entirelv  eti'aeetl. 

The  figured  specimen  is  1!)  cm.  in  length,  and  was  probably  at  least  22 
cm.  in  length  when  entire.  It  is  about  7  cm.  broad  in  the  widest  part,  which 
is  above  the  middle  of  the  leaf.  Unfortunately  tlie  margin,  with  the  excep- 
tion of  a  small  portion  near  the  base,  is  destroyed,  and  consequently  it  is 
impossible  to  properly  characterize  this  leaf.  There  is,  however,  a  little 
evidence  to  show  that  the  margin  was  not  entire  for  the  whole  distance,  but 
this  is  too  vague  to  be  of  much  value. 

I  have  referred  this  leaf  provisionally  to  the  genus  Quercus,  from  its 
resemblance  to  certain  living  forms,  but  it  will  be  necessary  to  see  additional 
material  before  the  correctness  of  this  view  can  be  tested. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  top  of  bluff;  collected  by  F.  H.  Knowdton,  August,  1888. 

Quercus  furoinervis  Americana  Kn. 

PI.  LXXXVIII,  fig.  5. 

Quercus  furcinervis  americana  Kn.:  Bull.  U.  S.  Geol,  Surv.  No.  152,  p.  192,  1898. 
Quercus  furcinervis  Kossm.    Lesquereiix:  Cret.  and  Tert.  Fl.,  p.  2-14,  PI.  LIV,  tigs.  1,  2. 

The  specimen  here  figured  is  certainly  the  same  as  that  figured  by 
Lesquereux  (loc.  cit.,  PL  LIV,  fig.  1)  for  this  species. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  5;  collected  by  Ward  and 
Kuowlton,  August  19,  1887. 

Quercus  weedii  n.  sp. 

PI.  LXXXVII,  fig.  4. 

Leaves  membranaceous,  ovate,  rounded  at  base,  acuminate  at  apex, 
margin  strongly,  irregularly  toothed,  teeth  minutely  spiny-pointed;  nerva- 
tion pinnate;  midrib  straight;  secondaries  about  8  pairs,  alternate,  at 
an  angle  of  about  45°,  fiexuose,  craspedodrome,  entering  the  teeth  or 
forking  near  the  margin  and  the  branches  passing  into  the  teeth,  or  with 
strong  nervilles  crossing  between  2  secondaries  and  sending  a  branch  to 
the   intermediate    teeth;    nervilles    numerous,    strong,    at   various    angles, 

HON  XXXII,  PT  11 45 


706     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

percurrent  or  forked  and  broken;  finer  nervation  beautifully  preserved, 
forming  quite  regular,  large  areolte. 

This  beautiful  species  is  represented  by  a  considerable  number  of  more 
or  less  perfect  leaves,  the  best  of  which  is  figured.  This  figured  example 
is  11  cm.  in  length  and  nearly  6  cm.  in  width.  Others  are  only  7  cm.  long 
and  3.5  cm.  wide.     None  larger  than  the  one  figured  were  obtained. 

One  of  the  marked  features  of  this  species  is  the  number  of  teeth, 
there  being  quite  regularly  twice  as  many  as  the  number  of  secondaries. 
These  intermediate  teeth  are  usually  a  little  smaller  than  the  others,  and 
are  supplied  with  a  branch  from  the  middle  of  a  strong  nerville,  which 
crosses  between  2  secondaries  at  some  distance  below  the  margin.  This 
character  is  so  constant  and  so  peculiar  that  it  may  even  be  of  generic 
value,  but  for  the  present  the  species  may  be  retained  in  the  genus  Quercus. 

This  species  has  a  more  or  less  close  resemblance  to  a  number  of 
described  fossil  forms.  It  is,  for  example,  somewhat  like  Quercus  viburni- 
folia  Lx.,^  from  Golden,  Colorado,  Black  Buttes,  Wyoming,  etc.  This  is 
more  wedge-shaped  at  base,  has  more  irregular  teeth,  which  are  supplied 
by  branches  from  the  forking  secondaries.  Quercus  gronlandica  Heer  ^  as 
figured  from  Spitzbergen  also  belongs  to  this  group,  but  is  a  much  larger 
leaf,  with  relatively  smaller  teeth  and  forked  secondaries. 

The  very  nuich  larger  leaf  figured  l)y  Newberry  as  a  young  form  or 
variety  of  Plcdanus  liaydenii  Newbyl,  and  coming  from  the  Fort  Union 
beds  at  the  mouth  of  the  Yellowstone,  also  belongs  near  this  group.  It  is 
impossible  to  see  any  generic,  or  even  specific,  diff'erences  between  this 
figure  of  P.  limjdenii  and  Heer's  figure  above  referred  to  of  Quercus 
gronlandica.     They  must  certainly  be  the  same. 

All  of  the  species  mentioned  seem  to  be  very  close  to  the  one  under 
consideration,  but  they  diff'er  constantly  by  the  manner  of  the  supply  of 
nerves  to  the  secondary  teeth. 

I  have  named  this  species  in  honor  of  Mr.  Walter  Harvey  Weed,  who 
collected  the  best  specimen  observed. 

Habitat:  Fossil  Forest  Ridge,  middle  stratum;  collected  by  W.  H. 
Weed.  Bed  No.  6,  "Platanus  bed;"  collected  by  Ward  and  Kuowlton, 
August  19,  1887. 

I  Tert.  Fl.,  p.  159,  PI.  XX,  fig.  11. 

=  F1.  Fobs.  Arct.,  Vol.  II,  Mioc.  Fl.  Spitzb.  (K.  Veteusk.  Akad.  Handl.,  Vol.  VIII,  No.  7),  V\.  XII,  fig.  5. 

siUustratlous  Cret.  and  Tert.  Fl.,  PI.  XXI. 


FOSSIL  FLORA.  707 

QuEKcrs  sp. 
PI.  LXXXIX,  fig.  7. 

This  is  a  tragment  ot"  the  base  of  what  appears  to  have  been  a  lavge, 
thick  leaf.  It  lias  a  thick  midrib,  and  alternate,  thin,  parallel,  straight 
secondaries,  which  arise  at  an  angle  of  about  45°.  None  of  the  finer 
nervation  is  preserved. 

This  has  some  resemblance  to  the  basal  portion  of  what  has  been 
described  as  Q.  cidveri  (p.  708),  but  it  was  several  times  larger  than  this 
and  lacks  the  marginal  toothing.     They  come  from  the  same  beds. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  base  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

QuERCus  OLAFSENi  Heer. 

Qnercus  olafseni  Heer:  Fl.  Foss.  Arct.,  Vol.  I,  p.  109,  PI.  XLVI,  fig.  10.     Lesquereux: 
Cret.  and  Tert.  FL,  p.  22i,  PI.  XL VIII,  fig.  i;  p.  245,  PI.  LIV,  fig.  3. 

There  are  a  number  of  examples  of  this  species,  some  of  which  are 
very  well  preserved.  They  are,  with  the  exception  of  some  minor  details, 
identical  with  the  figures  given  by  Heer  and  Lesquereux.  Thus  only 
occasionally  are  they  doubly  dentate,  and  the  secondaries  rarely  branch. 
They  are  undoubtedly  the  same  as  the  leaves  figured  by  Lesquerevix. 

This  species  was  reported  by  Lesquereux  from  the  Bad  Lauds  of 
Dakota  (Fort  Union  group),  and  from  Table  Mountain,  California 
(Miocene?). 

Habitat:  Yellowstone  River,  one-half  mde  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August  27,  1888. 

QuERCUS    YANCEYI    U.  Sp. 
PI.  LXXXIX,  fig.  2. 

Leaf  of  firm  texture,  broadly  lanceolate,  somewhat  wedge-shaped  at 
base  and  acuminate  at  apex,  with  undulate  toothed  margin;  midrib  strong, 
straight;  secondaries  9  or  10  pairs,  alternate,  remote,  emerging  at  a  low 
angle,  curving  upward,  the  lower  ones  arching  along  the  border,  upper 
ones  entering  the  teeth  or  often  arching  along  and  joining  the  one  next 
above;  nervilles  few,  irregular,  broken;  finer  nervation  forming  irregular 
areolae. 


708  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  leaf  figured  is  the  only  one  of  this  species  observed.  It  is  10  cm. 
long  and  17  mm.  wide  in  the  broadest  part,  which  is  about  the  middle. 
The  entire  leaf,  witli  the  exception  of  a  fragment  at  the  base,  is  preserved. 
The  margin  is  entire  for  the  lower  third,  then  it  is  undulate-toothed,  the 
teeth  being  rounded  or  rarely  with  a  minute  sharp  point.  In  the  lower 
part  the  secondaries  arch  and  join,  while  those  above  either  enter  the  teeth 
or  join  by  a  long  loop  and  send  a  branch  from  the  outside  to  the  teeth. 
The  finer  nervation  is  well  preserved,  forming  irregular  meshes. 

This  beautiful  species  does  not  seem  to  be  very  closely  related  to  any 
fossil  oak  with  which  I  am  familiar.  Perhaps  its  nearest  relative  is  Q. 
laurifolia  Newby.,^  from  "burned  shales,  over  lignite  beds.  Fort  Berthold, 
Dakota,"  the  age  of  which  is  not  well  indicated,  but  is  certainly  Tertiary. 
It  has  only  very  faintly  undulate-toothed  margins,  and  the  secondaries  are 
at  a  more  acute  angfle  than  in  the  one  under  discussion. 

I  have  named  this  species  in  honor  of  Mr.  John  Yancey,  proprietor  of 
the  stage  station,  and  the  namer  of  the  fossil  forest  near  by. 

Habitat:  Yancey  Fossil  Forest;  slope  near  the  standing  trunks;  col- 
lected by  Lester  F.  Ward  and  F.  H.  Kuowlton,  August  10,  1887. 

QUERCUS    CULVERI    n.    sp. 
PL  LXXXVII,  (ig.  5. 

Leaf  small,  of  thick,  firm  texture,  approximately  oblong  in  general 
outline,  obscurely  3-lobed;  margin  strongly,  in-egularly  toothed;  teeth 
obtuse  or  rounded,  pointing  outward,  separated  by  broad,  shallow  sinuses; 
petiole  slender;  midrib  rather  slender,  nearly  straight;  secondaries  6 
pairs,  subopposite,  emerging  at  an  angle  of  about  45°,  or  the  2  lower 
pairs  only  25°,  all  nearly  straight  and  entering  the  teeth ;  third  pair  of 
secondaries  longest,  entering  the  lateral  lobes,  with  branches  on  the  lower 
side  which  pass  to  smaller  teeth;  nervilles  strong,  apparently  broken ;  finer 
nervation  not  preserved. 

This  beautiful  species  is  represented  only  by  the  specimen  figured.  It 
is  a  small  leaf,  being  about  7.5  cm.  long,  including  the  petiole,  which  does 
not  seem  to  be  entirely  preserved,  and  5  cm.  broad  bewteen  the  lateral 

'  Proc.  U.  S.  Nat.  Mus.,  1882,  p.  50.5;  Plates  ined.,  PI.  LIX,  fig.  5. 


FOSSIL  FLOKA.  701> 

lobes.  As  already  stated,  the  leaf  is  ol)srurely  ()l)l(»iig  in  g'eneral  outline, 
beinp:  sli<rhtly  wedgx'-shajied  at  base  and  having  the  strongest  teeth  or 
lateral  lo])es  at  about  two-thirds  of  the  distance  from  tlie  base.  The  apex 
is  not  preserved,  but  judging  from  the  contour  it  must  have  been  rather 
obtuse.  The  teeth  of  the  margin  are  also  rather  obtuse.  The  nervation  is 
strongly  craspedodrome,  tlie  secondaries  or  branches  all  entering  the  teeth. 
Oidy  a  few  nervilles  are  preserved  and  those  appear  broken.  None  of  the 
ultimate  nervation  has  been  preserved. 

This  species  is  quite  unlike  any  American  fossil  species  with  whicli  I 
am  familiar.  Among  living  species  it  approaches  quite  closely  to  occasional 
leaves  of  Q.  prinoides  Willd.,  of  the  eastern  United  States.  The  living 
leaves  incline  to  be  more  wedge-shaped  at  base  and  to  have  stronger  teeth 
separated  by  deeper  sinuses.  It  is  hardly  probable  tliat  the  resemblance  is 
close  enough  to  warrant  the  assumption  that  Q.  prinoides  has  actually 
descended  from  this  fossil  form. 

I  take  pleasure  in  having  named  this  fine  species  in  honor  of  Prof. 
George  E.  Culver,  some  time  professor  of  geology  in  the  University  of  South 
Dakota,  who  assisted  me  in  making  the  collection  of  plants  in  the  Yellow- 
stone National  Park. 

Habitat:  Bank  of  Yellowstone  River,  one-half  mile  below  the  mouth 
of  Elk  Creek ;  top  of  bluff  300  feet  above  stream,  in  white,  coarse-grained 
tuff;  collected  August  28,  1888,  by  F.  H.  Knowlton  and  G.  E.  Culver. 

QUERCUS    HESPERIA    n.  Sp. 

Leaf  of  firm  texture,  broadly  lanceolate  in  outline,  passing  from  about 
the  middle  down  into  a  long  wedge-shaped  base,  rather  abruptly  pointed  at 
apex;  margin  with  few  (8  to  10)  strong,  sharp,  upward-pointing  teeth; 
midrib  strong;  secondaries  10  to  12  pairs,  alternate,  straight  or  slightlj" 
curving,  ending  directly  in  the  teeth;  intermediate  secondaries  frequent, 
aboiit  midwa}'  between  the  secondaries,  disappearing  about  halfway  between 
midrib  and  margin;  nervilles  irregular,  producing  large,  coarse  areolation; 
finer  nervation  similar. 

The  specimen  upon  which  this  species  is  founded  is  nearly  perfect, 
lacking  only  the  tip.  It  is  6  cm.  long  and  a  little  more  than  2  cm.  wide. 
The  lower  half  of  the  leaf  is  regularly  wedge-shaped  and  the  upper  portion  is 


710     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

apparently  rather  abruptly  pointed.  The  teeth  are  strong  and  sharp-pointed, 
with  rounded  sinuses. 

This  species  seems  to  be  allied  to  Q.  hoiveniana  Lx.,'  from  California,  but 
differs  essentially  in  having  much  larger,  sharper  teeth  and  straight 
secondaries.  It  is  also  allied  to  Q.  yanceyi  which  has  undulate  or  slightly 
toothed  margin  and  fewer,  more  curved  secondaries.  It  somewhat 
resembles  a  leaf  that  has  been  described  as  Hicoria  culveri,  which,  however, 
differs  in  the  teeth,  and  in  having  a  camptodrome  instead  of  a  craspedodrome 
nervation. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
at  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Dryopyllum  longipetiolatum  n.  sp. 
PL  LXXXVIIl,  figs.  6,  7. 

Leaves  lanceolate,  long  wedge-shaped  at  base,  long  narrowly  acuminate 
at  apex,  margin  regularly  undulate-toothed,  the  teeth  sharp,  upward  point- 
ing, separated  by  rather  shallow  sinuses  ;  petiole  very  long,  slender ;  midrib 
thick,  straight;  secondaries  numerous,  alternate,  12  pairs  or  more,  at  a  low 
angle  in  the  lower  part,  more  acute  above,  slightly  curving  outward  in 
passing  to  the  margin,  all  ending  in  the  teeth ;  nervilles  at  right  angles  to 
the  secondaries,  obscure  but  apparently  mainly  percurrent ;  finer  nervation 
destroyed. 

This  species  is  represented  by  a  number  of  specimens,  none  of  which 
are  complete  in  a  single  example,  but  by  combining  several  a  good  idea  of 
the  species  is  given.  The  length  appears  to  have  been  about  20  cm.  and 
the  Avidtli  in  the  middle  4  cm.  The  petiole  is  long,  being  2.5  cm.,  and  pos- 
sibly not  all  preserved.  In  the  larger  leaves  the  secondaries  are  quite 
remote  and  distinctly  alternate.     They  arch  slightly  in  passing  to  the  teeth. 

The  leaves  of  this  species  were  at  first  confounded  with  leaves  of 
Castanea  imkliella,  with  which  they  occur  in  the  same  beds,  but  they  differ 
in  the  longer  petiole,  the  smaller  teeth,  and  in  the  irregular,  arching 
secondaries,  with  an  occasional  intermediate  secondary  between.  The 
teeth  of  the  upper  third  of  the  leaf  are  also  of  a  different  character. 

'  Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  No.  2,  p.  6,  PI.  II,  figs.  5,  6. 


FOSSIL  FLOUA.  711 

Anioii'''  s])ecies  of  Dry()i)liylluiu  this  species  has  some  resemblance  to 
D.  (tquumarum  WanP  from  Black  Buttes,  Wyoming.  The  latter  differs  in 
being  broadest  below  the  middle,  undulate  or  sinuate  toothed,  and  in  having 
more  numerous,  often  camptodrome,  secondaries.  D.  suhfalcatum  Lx.,^  from 
Point  of  Rocks  and  Hodges  Pass,  Wyoming,  also  has  some  resemblance, 
but  is  nuxch  smaller,  with  more  numerous  close  secondaries. 

Habitat :  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  7, 
"  Castanea  bed ;"  collected  by  Lester  F.  Ward  and  F.  H.  Kuowlton,  August 
16-20,  1887. 

ULMACEiE. 

Ulmus  pseudo-fulva!  Lx. 
PI.  LXXXVm,  flg.  2. 

Ulmus  pseudo-fulva  Lx. :  Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  p.  16,  PI.  IV,  fig.  3,  1878. 

The  fragment  figured  is  all  that  has  been  found  of  this  form,  and  it  is 
doubtfully  referred  to  this  species. 

Habitat:  Lamar  River,  between  Cache  andCalfee  creeks,  Yejlowstone 
National  Park;  collected  by  F.  H.  Knowlton,  August,  1888. 

Ulmus  minima?  Ward. 

Ulmus  minima  Ward:  Types  of  the  Laramie  FL,  p.  45, PI.  XXII,  figs.  3,  4. 

A  single  small  broken  specimen  is  referred  doubtfully  to  this  species. 
It  is  of  about  the  same  size,  but  has  the  secondaries  at  a  little  lower  anarle, 
and  has  the  nervilles  well  preserved.  They  are  strong  and  percurrent. 
The  margin  is  toothed,  but  the  teeth  are  not  well  preserved. 

This  leaf  is  found  on  the  same  piece  of  matrix  with  Ficus  tUmfolial 
Al.  Br. 

Habitat:  Mountain  back  of  Yancey s,  near  the  fossil  trees;  collected  by 
F.  H.  Knowlton,  August,  1888. 

'  Types  of  the  Laramie  Fl.,  p.  26.  PI.  X,  figs.  2-4. 

^Cf.  D.  hruneri  Ward,  now  referred  to  D.  suhfalcatum:  Types  of  the  Laramie  Fl.,  p.  27,  PI.  X, 
figs.  5-8. 


712     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Ulmus  rhaminfolia?  Ward. 
Ulmus  rhaminfoKa  Ward:  Types  of  the  Laramie  FL,  p.  45,  PL  XXIII,  fig.  5. 

This  species  is  also  represented  by  a  single,  much  broken  leaf,  with  only 
a  small  portion  of  the  margin  preserved.  It  has  the  size  and  nervation  of 
Professor  Ward's  species,  and  is  with  hardly  any  doubt  the  same. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Ulmus,  fruits  of. 
PI.  LXXXVIII,  figs.  3,  4. 

As  it  is  impossible  to  determine  the  species  of  Ulmus  to  which  these 
fruits  belong,  or  properly  to  characterize  them,  I  have  preferred  to  leave 
them  imnaraed  specifically. 

Habitat:  Yellowstone  River  one-half  mile  below  mouth  of  Elk  Creek, 
top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Planera  longifolia  Lx. 

Planera  longifolia  Lx.:  Tert.  Fl.,  p.  189,  PL  XXVII,  figs.  4-6;  Cret.  and  Tert.  FL, 
p.  161,  PI.  XXIX,  figs.  1-13. 

The  collection  contains  some  40  more  or  less  well-preserved  examples 
of  this  species,  which  agree  very  well  indeed  with  the  various  figures 
given  by  Lesquereux.  A  number  are  so  well  preserved  that  the  finer 
nervation  is  retained.  The  nervilles  are  numerous,  parallel,  and  mainly 
percurrent. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  3  (30  specimens);  bed  No.  5 
(10  specimens);   collected  by  Ward  and  Knowlton,  August,  1887. 

ITRTICACE;E. 

FiCUS    DEFORMATA  U.  Sp. 
PL  XGI,  fig.  2. 

Leaf  large,  thick,  long-obovate,  slightly  unequal-sided  at  base,  abruptly 
rounded  above  to  an  obtuse  apex  and  rather  abrupt!}'  narrowed  below; 
margin  entire,  conspicuously  indented  or  deformed  on  one  side,  the  margin 
of  indentation  rounded;  midi-ib  thick;  secondaries  thick,  10  or  12  pairs, 


FOSSIL  FLORA.  713 

alternate,  onicrfrino-  at  an  anp-lo  of  35"  to  4")°,  curving'  upward,  campto- 
dronie;   none  of  the  liner  nervation  ])rewerve(I. 

This  leaf  is  l^^.f)  cm  long  and  almost  8  cm.  wide  in  the  broadest  part, 
wliioh  is  high  above  the  middle  of  the  blade.  It  is  long-obovate,  obtuse  at 
apex,  and  very  bioadly  or  obtusel}'  wedge-shaped  at  base.  The  margin  is 
entire  except  for  a  curious  indentation  on  one  side,  Avhich  has  probably 
resulted  froin  an  injury  of  some  sort.  This  indentation  passes  nearly  to  the 
midrib  and  has  rounded  lobes.  The  secondaries  adjacent  to  this  are  also 
distorted,  being  much  curved.     The  finer  nervation  is  not  preserA'ed. 

It  is  possible  tliat  the  fragment  of  the  base  of  a  leaf  described  and 
figured  on  PL  LXXXIX,  fig.  7,  is  the  same  as  this  species,  but  it  is  obvi- 
ously impossible  to  be  certain  of  this.  It  is  also  undoubtedl)-  related  to, 
and  is  possibly  identical  with,  F.  asimirKvfoJia  Lx.,'  from  Placer  Count}', 
California.  This  has  the  same  shape  and  nervation,  but  for  obvious  reasons 
it  is  best  to  keep  them  separate,  at  least  until  additional  specimens  can  be 
obtained. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
base  of  blutf;  collected  by  F.  H.  Knowlton. 

FiCUS    UNGERI  Lx. 

PI.  XCI,  fig.  .3. 

Ficus  ungeri  Lx.:  Tert.  FL,  p.  195,  PL  XXX,  flg.  3;    Cret.  and  Tert.  FL,  p.  10.3,  PL 
XLIY,  figs.  1-3. 

Habitat:  Yellowstone  River,  1  mile  below  mouth  of  Elk  Creek,  west 
side;  and  about  same  distance  above  Hellroariug  Creek;  collected  by 
F.  H.  Knowlton,  August  4,  1888. 

Ficus  sp. 

PL  LXXXIX,  fig.  3. 

This  is  too  fragmentary  to  ])ermit  even  the  generic  determination,  but 
it  seems  to  belong  to  Ficus.  It  consists  of  the  base  of  a  thick  leaf  having 
a  thick  midrib,  with  rather  thin  parallel  secondaries  and  a  short  very  thick 
petiole. 

Habitat :  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
base  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

1  Cret.  and  Tert.  Fl.,  PI.  LVI,  fig.  3. 


714     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

FiCUS    SHASTENSIsf  Lx. 
Ficus  shantensis  Lx. :  Proc.  U.  S.  Nat.  Mus.,  Vol.  XI,  1888,  p.  28,  PI.  XI,  fig.  3. 

This  species  was  described  by  Lesquereux  from  Shasta  County,  Cali- 
fornia. It  was  said  to  be  6  cm.  long-  and  3.5  cm.  broad,  and  with  a  very 
thick  petiole.  The  Park  leaf  is  8  cm.  long  and  4.5  cm.  wide,  and  lacks  the 
petiole.  The  nervation  appears  identical,  but  I  have  hesitated  to  make  a 
positive  identification  on  such  scanty  material. 

Habitat:  Lamar  River,  between  Cache  and  Calfee  creeks,  on  the  same 
piece  of  matrix  as  Salix  angusta  and  Lygodium  kaulfusu ;  collected  by  F.  H. 
Knowlton,  August  27,  1888. 

Ficus  sordida  Lx. 
Ficus  sordida  Lx. :  Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  No.  2, 1878,  p.  17,  PI.  IV,  figs.  6, 7. 

A  single  fragment,  representing  the  lower  side  of  a  leaf  of  about  the 
same  size  and  nervation  as  fig.  7  of  Lesquereux's  plate. 

Habitat:  Specimen  Ridge,  Fossil  Forest,  "Platanusbed;"  collected  by 
Ward  and  Alderson,  August  25,  1887. 

Ficus  densifolia  n.  sp. 

PI.  LXXXIX,  fig.  1;  PI.  XC,  figs.  1,2;  PI.  XCI,  fig.  1. 

Leaves  large,  very  thick,  unequal-sided,  irregular  long-obovate, 
broadest  at  or  above  the  middle,  obtuse  above,  nan-owed  below  to  a 
rounded  truncate  or  sHghtly  heart-shaped  base;  margin  entire  or  very 
slightly  undulate;  petiole  not  preserved;  midrib  very  thick,  sHghtly 
flexuose;  secondaries  8  or  9  pairs,  lower  opposite  or  subopposite,  others 
alternate;  loAver  secondaries  thin,  nearly  at  a  right  angle  with  midrib, 
otliers  irregular,  remote,  at  various  angles,  much  arching  upward,  occa- 
sionally forked,  all  camptodrome,  and  joining  by  broad  loops;  middle 
secondaries  sometimes  branched  on  the  outside,  the  branches  joining  by 
broad  loops  near  the  margin;  nervilles  strongly  marked,  mainly  broken, 
producing  by  union  large  quadi-angular  areas;  finer  nervation  producing 
irregular  quadrangular  areas. 

This  fine  species  diff'ers  markedly  from  all  others  obtained  in  the 
Yellowstone  National  Park,  and  is  quite  unlike  any  American  form.  The 
smaller  leaves  are  13  or  14  cm.  long  and  5  or  6  cm.  broad,  while  the  larger 


FOSSIL  FLOUA.  715 

exampk's  are  fully  25  cm.  lonj:;'  and  nearly  or  ([uite  10  cm.  broad.  They 
are  broadly  obovate,  being-  broadest  usually  above  the  middle.  At  base 
the  leaves  are  narrowed  into  a  small  rounded,  truncate,  or  even  heart- 
shaped  part.  Above  they  appear  rather  abruptly  naiTOwed  into  an  obtuse 
apex. 

The  nervation  is  strongly  marked.  The  midrib  is  very  thick,  as  are 
most  of  the  secondaries,  especially  in  the  middle,  when  they  pass  to  the 
broad  portion  of  the  blade.  They  are  then  alternate,  thick,  and  sometimes 
forked,  and  not  rarely  branched  on  the  outside.  The  secondaries  and  their 
branches  are  arched  and  joined  by  broad  bows. 

Habitat:  Southeast  side  of  Crescent  Hill,  largest  specimen  (PI. 
LXXXIX,  tig.  1) ;  Yellowstone  River,  one-half  mile  below  mouth  of  Elk 
Creek,  one  peculiar,  somewhat  doubtful,  specimen;  also  one  from  base  of 
bluff  (PI.  XC,  fig.  1);  hill  above  Lost  Creek,  typical  specimen.  All  of  the 
above  collected  by  F.  U.  Knowlton,  August,  1888.  Specimen  Ridge,  Fossil 
Forest,  opposite  Slough  Creek,  "Platanus  bed"  and  bed  100  feet  above 
same;  specimens  numerous;  collected  by  Lester  F.  Ward  and  E.  C. 
Alderson,  August  25,  1887.  Fossil  Forest  Ridge,  bed  No.  5,  "Sahx  bed," 
one  broken  specimen;  collected  by  Ward  and  Knowlton,  August  9,  1887. 

FiCUS   HAGUEI  n.   s-p. 

PI.  XG,  fig-.  3. 

Leaf  thick,  broad,  rounded-ovate,  apparently  rounded  and  truncate  at 
base  and  rather  abruptly  acuminate  at  apex;  margin  entire;  midrib  thick, 
perfectly  straight;  leaf  palmately  3-ribbed  from  above  the  base,  appar- 
ently a  pair  of  thin  secondaries  originating  from  or  near  the  base  of  the 
lamina,  then  a  pair  of  very  strong  subalternate  ribs  or  secondaries,  at  an 
angle  of  about  45°,  which  arch  upward;  above  this  pair,  in  the  upper 
part  of  the  blade,  are  4  or  5  pairs  of  alternate  thinner  secondaries  at  a 
lower  angle;  all  of  the  secondaries  are  joined  some  distance  from  the 
margin  by  a  broad  loop,  with  another  series  of  smaller  loops  outside 
these,  at  least  in  the  lower  portion  of  the  leaf;  a  number  of  irregular  inter- 
mediate secondaries  occur  between  the  primary  secondaries;  nervilles  thin, 
irregular. 

The  specimen  figured  is  the  only  representative  of  this  strongly  char- 
acterized species.     It  unfortunately  lacks  both  base  and  apex,  but  the  por- 


716     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

tion  preserved  is  8  cm.  long  and  nearly  8  cm.  wide.  There  is,  of  course, 
no  means  of  knowing  the  configuration  of  base  and  apex,  but  from  all 
indications  it  is  probable  that  the  base  was  rounded-truncate  and  the  apex 
abruptly  acuminate.  It  is  well  characterized  by  secondaries,  of  which  the 
lower  prominent  pair  are  strongest  and  arch  up  and  join  by  a  broad  loop 
to  the  secondaries  above,  producing  a  palmately  ribbed  leaf 

I  am  uncertain  as  to  the  correctness  of  this  generic  reference,  but  it 
seems  to  apjjroach  closer  to  Ficus  than  any  other.  In  any  case,  it  is  so 
well  marked  that  it  can  be  readily  recognized.  It  does  not  appear  closely 
related  to  any  fossil  species  with  which  I  am  familiar,  but  among  living 
species  it  has  considerable  resemblance  to  F.  nodosa  Tey.  and  Binu.,  and 
F.  procera  R.,  both  from  British  India. 

The  species  is  named  in  honor  of  the  discoverer. 

Habitat:  Fossil  Forest  Ridge,  middle  stratum;  collected  hy  Xn\o\di 
Hague,  September  21,  1884. 

Ficus  tili^efoliaI  A1.  Br. 

A  fragment  of  the  basal  portion  of  a  large  leaf,  apparently  of  this 
species.  It  is,  for  example,  very  much  like  the  figure  given  by  Lesquereux,^ 
from  the  Auriferous  gravels  of  California. 

Habitat:  Hill  above  Yancey s  and  near  the  fossil  trees;  collected  by 
F.  H.  Knowlton,  August,  1888. 

Ficus  AsmiNiEFOLiA  Lx. 

Ficiis  asiminmfoUa  Lx.:  Cret.  and  Tert.  Fl.,  p.  2o0,  PI.  LVI,  tigs.  1-3. 

A  single  deformed  leaf,  which  agrees  in  nervation  with  this  species  and 
with  the  upper  portion  of  another  perfect  leaf 

Habitat:  Fossil  Forest  Ridge,  bed  No.  3,  "Magnolia  bed;"   collected 

by  Ward  and  Knowlton,  August,  1887.     Yellowstone  River,  one-half  mile 

below  mouth  of  Elk  Creek,  base  of  bluff;  collected  by  F.  H.  Knowlton, 

August,  1888. 

Aetocarpus?  quercoides  n.  sp. 

PL  XCII,  fig.  1. 

Leaf  large,  thick,  5  (7?)-lobed,  lower  lobes  large,  rounded;  upper 
lateral  lobes   smaller,  turning  upward,  of  about  the  same   size  at  apex  as 

'  Mem.  Mu8.  Comp.  Zool.,  Vol.,  VI.  No.  2,  p.  18,  PI.  IV,  fig.  8, 1878. 


FOSSIL  FLOUA.  717 

central  or  torininal  1(>1)0,  all  separated  l)y  broad,  ntunded  sinuses;  midrib 
very  thick  below  and  to  the  middle  of  the  leaf,  from  which  ])oint  it  raj)idly 
diminishes  to  the  apex;  secondaries  nnmeroiis,  alternate,  at  angle  of  30° 
to  45°,  about  4  in  each  lobe,  except  the  small  central  lobe,  the  njjper 
ones  passing-  to  tlie  apex  of  the  lobe,  the  other  curving  near  the  margin 
below  it;  short  secondaries  pass  up  to  and  arch  along  above  the  sinuses, 
occasionally  in  the  upper  part  forking  and  passing  on  both  sides;  nervilles 
strong,  percurrent,  nearly  at  right  angles  to  the  secondaries;  finer  nervation 
not  preserved. 

The  specimen  figvxred  is  the  only  one  obtained  of  this  remarkable  and 
highly  cliaracteristic  leaf.  It  is  not  ]jerfect,  yet  it  appears  to  represent 
practically  all  of  the  leaf.  The  part  preserved  is  14  cm.  long  and  9.5  cm. 
broad  between  the  upper  lobes.  It  was  probably  at  least  17  cm.  in  length, 
and  if  tliere  were  7  lobes  it  was  of  course  nmcli  larg-er.  It  was  probably 
12  to  14  cm.  broad  between  the  lower  lobes.  The  width  at  the  middle 
sinus  is  a  little  less  than  3  cm.  It  is  strongly  5-lobed,  and,  following  the 
analogy  of  Artocarpus  lessigiana  (Lx.)  Kn.,  may  have  been  7-lobed. 
There  is,  however,  no  evidence  that  it  had  more  than  5  lobes.  The 
lower  lobe  is  5.5  cm.  wide  at  a  distance  of  1.5  cm.  from  the  midrib, 
while  the  upj^er  lateral  lobe  is  fully  6  cm.  wide  at  the  same  distance  from 
the  midrib.  The  extreme  length  of  the  ujjper  lobe  is  less  than  5  cm.,  the 
apex  being  curved  around  and  up.  The  secondaries,  as  pointed  out  in  the 
diagnosis,  are  about  4  in  number  in  each  lobe.  They  are  about  1  cm. 
apart,  the  upper  one  only  entering  the  apex  of  the  lobe.  The  only  trace  of 
the  finer  nervation  consists  of  a  few  strictly  percurrent  nervilles. 

I  am  in  doubt  as  to  the  proper  generic  reference  of  this  leaf.  When  it 
was  collected  in  the  field,  the  conclusion  was  hastily  formed  that  it  was  an 
oak,  but  the  nervation  is  not  at  all  that  of  this  genus.  It  seems  to  have  rather 
a  moraceous  character,  but  I  have  not  been  entirely  successful  in  finding 
affinities.  It  has  some  resemblance  to  species  of  Ficus,  but  on  the  whole 
approaches  closest  to  Artocarpus.  Compared  with  living  species  it  is  of 
the  A.  incisa  type,  yet  of  course  difi'ers  in  marked  peculiarities,  having,  for 
example,  only  five  instead  of  many  lobes.  Among  fossil  species  this  undoubt- 
edly approaches  A.  lessigiana  (Lx.)  Kn.,^ found  in  the  Laramie  and  Denver 
formations  of  Colorado,  Wyoming,  etc.    The  Yellowstone  leaf  has  much  the 


'  Science,  Vol.  XXI,  p.  24. 


718     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

shape  and  thick  iiiidril)  of  the  other,  but  difters  essentially  in  having-  3 
or  4  secondaries  instead  of  1  in  each  lobe.  It  is,  however,  a  leaf  suf- 
ficiently well  characterized  to  permit  it  to  be  readily  recognized,  and  if 
material  is  hereafter  found  that  will  throw  additional  light  on  its  affinities, 
it  can  be  easily  transferred  to  its  proper  genus.  For  the  present  it  may 
remain  under  Artocarpus. 

Habitat:  Yellowstone  River,  one-half  mile  below  moutli  of  Elk  Creek; 
collected  by  F.  H.  Knowlton,  August,  1888. 

magnoliacej:. 

Magnolia  californica  ?  Lx. 

Magnolia  californica  Lx. :  Foss.  PI.  Aurif.  Gravels,  Meiu.  Mus.  Comp.  Zool.,  Vol.  VI, 
No.  2,  1878,  p.  25,  PI.  VI,  figs.  5-7. 

A  single  specimen,  of  which  only  the  upper  part  is  preserved.  It  has, 
so  far  as  can  be  made  out,  the  shape  and  nervation  of  this  species,  but  it  is 
so  much  broken  that  its  positive  identification  is  not  possible. 

Habitat:  Fossil  Forest  Ridge;   Hague's  No.  1960. 

Magnolia  spectabilis  n.  sp. 
PI.  XCIII,  figs.  1,2. 

Leaves  very  thick,  coriaceous;  broadly  elliptical-lanceolate  in  outline, 
with  regularly  rounded  base  and  rather  abrupt  obtusely  acuminate  apex; 
margin  perfectl}^  entire,  not  undulate;  midrib  thick,  straight;  secondaries 
about  18  or  20  pairs,  alternate,  regular  and  j^arallel  or  slightly  irregular 
on  emergence  from  the  midi-ib,  becoming  parallel  above;  secondaries  either 
forking  near  the  margin  or  arching  along  and  joining  the  one  next  above 
in  a  series  of  loops,  with  a  series  of  smaller  loops  outside;  intermediate 
secondaries  usually  numerous,  sometimes  passing  nearly  to  the  junction  of 
the  primary  ones,  or  becoming  lost  at  one-half  or  two-thirds  of  the  distance 
from  midrib  to  margin,  irregular  and  not  parallel  to  other  secondaries; 
nervilles  numerous,  irregular,  broken,  approximately  at  right  angles  to 
the  secondaries;  finer  nervation  beautifully  preserved,  forming  strongly 
marked  quadrangular  areolae. 

This  fine  species  is  represented  by  a  large  number  of  well-preserved 
specimens.     The  larger  leaves  are  fully  20  cm.  long  and  7  or  8  cm.  wide, 


FOSSIL  FLORA.  719 

and  some  of  the  smaller  ones  12  or  15  cm.  long  and  4  to  6  cm.  wide.  The 
leaves  are  thick  and  leathery,  and  evidently  belonged  to  an  evergreen 
species. 

It  is  altogether  probable  that  the  leaves  obtained  by  Mr.  W.  H.  Holmes 
in  1878  from  Amethyst  Mountain  and  identified  by  Lesquereux  as  MafjnoUa 
lanceolata  Lx.,'  really  belong  to  this  species.  As  nearly  as  can  be  made 
out  from  Holmes's  description  of  the  locality,"  it  is  the  same  as  that  which 
afibrded  the  specimens  under  discussion.  But  a  careful  comparison  of  these 
lumierous  leaves  with  the  figures  given  by  Lesquereux,  as  well  as  with 
specimens  from  the  Auriferous  gravels,  makes  it  certain  that  they  can  not 
belong  to  M.  lanceolata.  Magnolia  spectabilis  differs  in  being  broader,  more 
I'ouuded  at  base,  with  secondaries  more  curved  and  with  numerous  inter- 
mediate secondaries.  A  still  greater  point  of  difference  is  in  the  texture  of 
the  leaf.  Of  M.  lanceolata,  Lesquereux  says:^  "This  leaf  is  not  coriaceous, 
rather  of  a  thin  substance,"  while  M.  spectahilis  is  thick  and  distinctly  coria- 
ceous or  leathery.  The  finer  nervation  is  not  preserved  in  M.  lanceolata, 
so  it  is  not  possible  to  compare  that  point. 

From  further  evidence  it  appears  that  these  identical  specimens  were 
again  submitted  to  Lesquereux  in  1887,  and  he  then  identified  them  with 
M.  inr/lcfieldi  Heer,*  a  species  that  he  has  also  reported  from  Lassen  County, 
California,  Green  River  group,  etc.  It  is  certainly  much  more  closely 
related  to  this  than  to  M.  lanceolata,  as  maybe  seen  from  Heer's  figures^  and 
specimens  identified  with  it  from  California.  It  is  of  the  same  shape  and 
size  as  M.  spectahilis  and  is  described  as  being  coriaceous,  but  it  differs 
somewhat  in  having  the  secondaries  more  scattered,  apex  irregular,  etc. 
The  finer  nervation  also  differs.  They  are  undoubtedly  close,  but  seem  to 
be  sufficiently  distinct  for  specific  separation. 

Among  living  s]3ecies  the  affinity  of  31.  spectahilis  is  unquestionably 
with  M.  grandiflora  L.,  or  M.  fostida  Sargent,  as  it  is  now  called.  The  size, 
outline,  texture,  and  nervation  are  practically  the  same. 

According  to   Sargent,**  the   direct   ancestor  of  Magnolia  foetida  Avas 

'Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  p.  24,  PI.  VI,  fig.  4. 

^Twelfth  Ann.  Kept.  U.  S.  Geol.  and  Geog.  Surv.  Terr  ,  1878  (1883),  Pt.  11,  ji.  49. 

'Loc.  cit.,  p.  24. 

<Cf.  Proc.  U.  S.  Nat.  Mus.,  Vol.  X,  1887,  p.  46. 

i^Fl.  Foss.  Arct.,  Vol.  VII,  1883,  p.  121,  Pl.LXIX,  fig.  1;  PI.  LXXXV,  fig.  3;  PI.  LXXXVI,  fig.  9. 

'Silva  of  North  America,  Vol.  I,  p.  3. 


720     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

probably  M.  inglefieldi  as  exemplified  from  Greenland,  the  type  locality. 
As  already  pointed  out,  this  species  is  also  the  closest  relative  of  M.  spevtahilis, 
which  in  turn  is  closely  allied  to  M.  fcetida.  It  is  possible  that  31.  inglefieldi, 
the  earliest  arctic  representative,  was  pushed  down  by  the  invading  ice, 
occupying  under  a  slight  variation  (31.  spectabilis)  tJie  Yellowstone  National 
Park,  and  surviving  at  the  present  day  as  M.  fmtkla. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  3,  "Magnolia  bed;"  collected 
by  Ward  and  Knowlton,  August,  1887. 

Magnolia  mkrophylla  n.  sp. 

Leaf  thick,  elliptical-lanceolate  in  outline,  with  slightly  undulate  entire 
margin;  midrib  very  thick,  straight;  secondaries  4  or  5  pairs,  alternate, 
very  irregular,  at  an  angle  of  30°'  to  45°,  much  curved  upward,  forking 
near  the  margin,  the  fork  joined  by  the  branch  from  the  secondary  next 
below;  intermediate  secondaries  present,  irregular;  nervilles  irregular;  finer 
nervation  obscure. 

A  single  broken  fragment  is  the  only  example  of  this  species  observed. 
The  part  preserved  is  6  cm.  long  and  4  cm.  wide. 

This  leaf  was  associated  on  the  same  piece  of  matrix  with  31.  spectabilis, 
yet  differs  by  the  characters  enumerated. 

Habitat:  Fossil  Forest  Ridge,  b'xl  No.  3,  "Magnolia  bed;"  collected 
by  Ward  and  Knowlton,  August,  1887. 

Magnolia  culveri  n.  sp. 

PL  XCII,  fig.  5. 

Leaf  large,  membranaceous,  broadly  ovate,  truncate  at  base,  obtusely 
pointed  above;  petiole  short;  midrib  thin,  straight;  secondaries  6  or  7 
pairs,  alternate,  at  an  angle  of  40°  or  45°,  forking  some  distance  below  the 
maro-in,  camptodrome  by  broad  loops;  intermediate  secondaries  occasional, 
soon  lost  in  the  middle  area  between  the  secondaries;  nervilles  numerous, 
irregular,  thin,  broken;  finer  nervation  producing  large  irregularly  quad- 
rangular areas. 

The  specimen  figured,  which  is  that  best  preserved,  is  14  cm.  in  length, 
including  the  petiole,  but  lacks  the  apex.  It  must  have  been  some  15  cm. 
lono-  when  perfect.  It  is  broadest  just  below  the  middle,  where  it  is  8  cm. 
wide.     The  petiole  is  1  cm.  long  and  moderately  thick. 


FOSSIL  KLORA.  721 

This  fine  species  l)elon<i-s  certainly  to  the  g-emis  Ma<;-n()lia,  ;is  attested 
by  the  sha{)e  and  the  forking-,  caniptodrome  secondaries.  It  is,  liowever, 
quite  iinHke  any  of  the  other  species  found  in  the  YeUowstone  National 
Park.  Perhaps  its  closest  relation  is  J/,  californica  Lx.,^  from  the  Chalk 
Blutfs  of  California.  It  is  diti'erent  in  shape,  being  ovate  instead  of  broadly 
oval,  and  has  somewhat  difterent  secondaries.  The  large  quadrangular 
finer  nervation  is  similar  in  both. 

It  does  not  approach  very  closely  to  either  of  the  living  American 
species,  being  perhaps  closest  to  31.  acnminafa  L.,  the  well-known  cucumber 
tree.'  Tlie  shape  of  the  leaves  is  practically  the  same,  but  the  nervation 
differs  somewhat. 

I  have  named  this  species  in  honor  of  Prof.  George  E.  Culver,  who 
assisted  in  making  the  collection  from  this  place. 

Habitat:  East  bank  of  Lamar  River,  between  Cache  and  Calfee  creeks; 
collected  by  F.  H.  Knowlton  and  George  E.  Culver,  August,  1888. 

Magnolia  ?  pollardi  n.  sp. 
PL  LXXXI,  figs.  9,  10. 

Petals  of  firm  texture,  elliptical  or  elliptic-ovate  in  outline,  narrowed 
below,  rounded-obtuse  above;  nervation  of  numerous  apijroximately  par- 
allel nerves  about  2  mm.  apart. 

The  best  preserved  of  these  2  specimens  (tig.  9)  has  7.5  cm.  in  length 
preserved,  and  was  probably  fully  8.5  cm.  in  length  when  perfect.  It  is 
3  cm.  broad  in  the  middle,  and  is  narrowed  at  base  to  a  point  of  attach- 
ment some  5  or  6  mm.  broad.  The  upper  point  is  unfortunately  destroyed, 
but  it  seems  probable,  from  the  appearance  of  the  margin  and  nerves,  that 
it  was  obtuse.  The  nerves  arise  from  the  basal  part  and  run  approximately 
parallel,  spreading  slightly  in  the  middle  and  converging  toward  the  apex. 
In  the  middle  these  nerves  are  between  3  and  4  mm.  apart,  but  in  the  apex 
they  are  separated  by  only  about  2  mm.  There  is  some  evidence  of  inter- 
mediate nerves,  or  possibly  cross  veinlets,  but  these  are  so  indistinct  that 
a  positive  statement  concerning  them  can  not  be  made. 

The  other  specimen  (fig.  10)  is  a  trifle  over  5  cm.  in  length,  but  lacks 
both  upper  and  lower  parts.     It  was  probably  6.5  or  7  cm.  in  length  when 


■Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  No.  1,  p.  25,  PL  VI,  figs.  5,  7. 
=  Cf.  Sargent:  Silva  of  N.  A.,  Vol.  I,  Pis.  IV,  V. 
JION  XXXII,  PT  II 40 


722  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

perfect.  It  i.s  exactly  3  cm.  in  width  at  the  widest  portion,  which  is  a  httle 
aboA'e  the  middle.  There  is  no  indication  of  the  form  of  the  base,  as  it  is 
destroyed  The  apex  was  qnite  obviously  obtuse.  The  nerves  are  less 
distinctly  preserved  than  in  the  other  specimen,  but  by  careful  search  they 
can  be  made  out  as  shown  in  the  figure.  Beyond  these  nothing  can  be 
made  out. 

It  is  with  some  hesitation  that  these  specimens  are  desci'ibed  as  petals 
of  Magnolia.  They  were  at  first  supposed  to  be  spathe-like  growths  of 
some  monocotyledonous  plant,  and  their  identification  as  Magnolia  2)etals 
was  first  suggested  by  Mr.  C.  L.  Pollard,  of  the  United  States  National 
Museum,  in  whose  honor  I  take  pleasure  in  naming  the  species.  The 
probability  of  their  being  petals  of  a  large-flowered  Magnolia  is  greatly 
strengthened  by  the  fact  that  undoubted  Magnolia  leaves  in  abundance  are 
found  in  the  various  beds  of  the  Yellowstone  National  Park,  whereas  no 
n:ionocot5^1edouous  plant  has  been  found  to  which  these  apparently  could 
have  belonged.  There  is  a  facies  to  the  specimens  that  is  diflicult  to 
describe  and  wholly  impossible  to  show  in  a  figure,  which  is  very  sug- 
gestive of  Magnolia  petals.  The  manner  in  which  they  curve  and  narrow 
on  the  rock,  although  this  appearance  may  of  course  be  only  accidental, 
is  very  similar  to  the  petals  of  certain  large-flowered  forms — such,  for  exam- 
ple, aS'  M.  conspkua.  In  any  case  they  are  distinctive  forms  that  may  be 
readily  recognized,  and,  for  the  purposes  of  geologic  correlation,  are  of 
undoubted  value.  Several  botanists  to  whom  the  specimens  have  been 
submitted  agree  that  their  reference  to  Magnolia  is  fully  warranted,  and 
for  the  present  at  least  they  may  be  so  considered. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek  (fig.  10);  collected  by  F.  H.  Knowlton,  August,  1888.  Fossil  For- 
est Ridge,  opposite  Slough  Creek;  collected  by  Lester  F.  Ward,  August, 

1887. 

LAURACEiE. 

Laurus  primigenia?  Ung. 

PI.  XGI,  figs.  4,  5. 

Laurus  primigema  Ung.  Of.  Ward:  Types  of  the  Laramie  PL,  p.  47,  PI,  XXIII,  fig.  8. 

The  much  broken  specimens  are  the  only  ones  of  this  species  found. 

Their  identification  is  open  to  doubt,  yet  they  are  obviously  the  same  as 


FOSSIL  FLOHA.  723 

the  leaf  fi<>iirc(l  l)y  Pntfcssor  Ward  as  tliis  .s|)(H-i(.'.s  from  Carbon,  "Wyoniino-. 
]\[or('  iiiatcrial  will  l)e  in'ccssarv  Ijeforc  its  status  can  be  fixed  with  oertaiiitv. 
llal)itat:   Yellowstone   River,  half  a  mile  below  mouth  of  Elk  Creek, 
foot  of  bluff:   eolleeted  by  F.  H.  Knowlton,  August,  1888. 

LaURUS    PKRDITA    11.   SJ). 

I'l.  XCIV,  fig.s.  1-5. 

Leaves  coriaceous,  broadly  lanceolate,  wedg-e-shaped  at  base,  obtusely 
acuminate  at  apex;  margins  entire,  Ixit  very  slightly  undulate;  petiole 
short,  stout;  midril)  thick,  straiglu;  secondaries  7  or  8  pairs,  alternate, 
camptodrome,  arising,  at  an  angle  of  40°  or  45°  and  curving  upward  and 
archmg  along  near  the  margin  and  forming  numerous  broad  loops  or 
bows;  nervilles  numerous,  irregular,  mainly  forked,  ajjproximately  at  right 
angles  to  the  midrib;  finer  nervation  not  preserved. 

The  collection  contains  a  number  of  specimens  of  this  species,  none  of 
them,  however,  quite  perfect.  They  are  about  15  cm.  long  and  about 
4.5  cm.  ])road.  The  5  specimens  figured  show  well  the  character  of  the 
species.  They  are  broadly  lanceolate,  with  a  regularly  narrow-ed  base  and 
apparently  a  rather  obtuse  a}iex.  The  secondaries  are  about  7  pairs,  which 
arch  much  upward  and  along  the  l^orders.  The  nervilles  are  numerous, 
mainly  at  right  angles  to  the  midrib,  and  irregular  and  often  broken. 

This  species  has  some  resemblance  to  Laiinis  grandis  Lx.,^  from  the 
Auriferous  gravels  of  California,  differing  in  being  smaller,  narrower,  and 
not  so  obtuse  at  apex.  The  resemblance  is  close  enough,  however,  to  make 
it  reasonably  certain  that  the  2  species  are  quite  closely  related. 

Persea  pseudo-caroKneitsis  Lx.,2from  Table  Mountain,  California,  is  some- 
what similar,  but  difi'ers  in  being  broader,  more  obtuse,  and  in  having  finer 
nei'vation. 

Habitat:  Hill  above  Yanceys  and  near  the  standing  fossil  trees;  col- 
lected by  F.  H.  Knowlton,  August  28,  1888.  Near  same  locality;  collected 
by  George  M.  Wright,  September  24,  1885. 

'Cret.  and  Tert.  Fl.,  p.  251.  PI.  LVIII,  figs.  1,  3. 

^Mein.  Mus.  Comp.  Zoiil.,  Vol.  VI,  No.  1,  p.  19,  PI.  VII,  figs.  1,  2. 


724  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAKK. 

LaURUS    MONTANA    11.  Sp. 
PI.  XCV,  fig.  2. 

Leaves  larg-e,  evidently  coriaceous,  elliptical-lanceolate,  narrowed  grad- 
ually (!)  to  the  petiole  and  (?)  uj^ward  to  an  acuminate  apex  (!),  slightly 
unequal-sided  in  the  U2:)per  part ;  margin  entii'e;  midrib  thin,  straight;  second- 
aries 5  or  6  ]5airs,  alternate,  the  lower  at  a  A^ery  acute  angle,  upper  ones 
slightly  less  so,  all,  but  especially  the  lower  ones,  with  numerous  branches 
on  the  outside,  which  join  and  form  broad  loops  just  inside  the  margin; 
nervilles  strong, percurrent,  approximately  at  right  angles  to  the  secondaries; 
ultimate  nervation  not  [)reserved. 

The  leaf  by  which  this  fine  species  is  represented  unfortunately  lacks 
both  base  and  apex,  but  is  otherwise  well  preserved."  It  is  10  cm.  long  as 
now  preserved,  and  was,  when  entire,  probably  at  least  14  cm.  in  length. 
The  width  is  5.3  cm.  As  stated,  it  is  a  little  (3  inm.)  wider  on  one  side  of 
the  midrib  than  the  other,  making  it  slightly  unequal-sided.  The  nerva- 
tion is  peculiar,  c(insisting  of  about  5  pairs  of  secondai-ies,  of  which  the 
lower,  on  the  narrower  side  of  the  leaf,  l)egins  well  toward  the  base  and 
passes  up  to  the  middle  of  tlie  Ijlade,  with  numerous  branches  on  the  out- 
side at  right  angles  to  the  midrib.  The  lower  secondary  on  the  broad 
side  of  the  leaf  is  ver}'  thin  and  short,  and  anastomoses  with  a  branch 
from  the  lower  portion  of  the  second  secondary.  This  latter  is  strong,  and 
passes  above  the  middle  of  the  leaf,  and  has  only  4  or  5  branches  on  the 
outside,  all  being  at  an  acute  angle  with  the  midrib.  The  other  second- 
aries have  1  or  more  branches  on  outside,  and  also  a  number  of  strong 
nervilles. 

This  species  appears  to  be  related  to  some  of  the  forms  figured  by 
Lesquereux  as  Laiirus  grandis,^  from  California,  and  may  possibly  be  an 
anomalous  form  of  this  species.  It  is  larger,  more  rounded,  slightly  unequal- 
sided,  and  has  quite  different  nervation.  It  also  resembles  L.  califonuca  Lx.,^ 
from  the  same  place. 

Habitat:  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
base  of  liluff;  collected  by  F.  H.  Knowlton,  August,  1888. 


'Cret.  and  Tert.  Fl.,  PI.  LVIII,  fig.  3. 
'Op.  rit.,  PI.  LVIII,  tig.  8. 


FOSSIL  FLOKA.  725 

Laurus  princeps  Heer. 
PI.  XCV,  (ig. .}. 

Ltiiinis  2)nnceps  Heer.    Lesqixereux :  Cret.  and  Tert.  Fl.,  p.  2.")1,  PI.  LVIII,  fig.  2. 

Till'  tine  leaf  shown  in  the  plate  iis  absolutely  perfect.  It  has  the 
same  size,  shape,  and  nervation  as  tig.  2  of  Lesquereux's  plate  (loc.  cit.). 

Habitat:  Yellowstone  River,  one-half  mile  below  month  of  Elk  Creek, 
base  of  blntt';  collected  by  F.  H.  Knowlton,  Aug-nst,  1888. 

Laurus  californica  Lx. 

Laurus  californica  Lx.:  Ciet.  and  Tert.  Fl.,  p.  250,  PI.  LYII,  fig.  3;  PI.  LYIII,  figs. 
0-8. 

Habitat:  Fossil  Forest  Ridge,  beds  Nos.  3,  5,  and  G;  Specimen  Ridge, 
Fossil  Forest,  opposite  Slough  Creek;  collected  by  Ward  and  Knowlton, 
August,  1887.  Northeast  side  of  Crescent  Hill,  opposite  small  pond, 
altitude  7,500  feet;  collected  August  2,  1888,  by  F.  H.  Knowlton  and 
G.  E.  Culver. 

Laurus  grandis  Lx 

PI.  XCIII,  fig.  3;  PL  XCV,  fig.  1. 
Laurus  grandis  Lx. :  Cret.  aud  Tert.  FL,  p.  251,  PL  LVIII,  figs.  1,3. 

Habitat:  Fossil  Forest  Ridge,  beds  Nos.  3,  .5,  aud  7;  collected  by 
Ward  and  Knowlton,  August,  1887.  Specimen  Ridge,  Fossil  Forest,  head 
of  Crystal  Creek;  collected  by  Ward  and  Alderson,  August  25,  1887. 
Hill  above  Lost  Creek;  collected  by  George  M.  Wright,  September  24, 1885. 

Perse  A  pseudo-carolinensis  Lx. 

PL  XCV,  fig.  4. 

Persea  pseudo-carolinensis  Lx. :  Auriferous  Gravels  of  California,  Mem.  Mus.  Comp. 
ZooL,  Vol.  VI,  No.  1,  p.  19,  PI.  VII,  figs.  1,  2. 

The  specimen  figured,  which  is  the  best  one  found,  agrees  closely  with 
the  figure  of  this  species  given  by  Lesquereux  (loc.  cit.,  fig.  1). 

Habitat:  Specimen  Ridge,  Fossil  Forest,  head  of  Crystal  Creek;  col- 
lected by  Ward  and  Knowlton,  August  25,  1887.  East  bank  of  Lamar 
River,  between  Cache  and  Calfee  creeks;  collected  by  F.  H.  Knowlton, 
August  21,  1888. 


726     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

!MaLAPOENNA    LAMARENSIS   11.  sp. 
PI.  XOIII,  figs.  4,  5;  PI.  XCVI,  fig.  5. 

Leaves  thick,  coriaceous,  ovate-oblong,  tapering  downward  to  a  long 
wedge-shaped  base  and  upward  to  an  acuminate  or  obtusely  acuminate 
apex;  margin  entire;  midrib  thick,  straight;  nervation  pinnate,  consisting 
of  2  pairs  of"  opposite  thick  ribs  or  secondaries,  of  wdiich  the  lower  pair 
arise  near  the  base  and  pass  up  for  nearly  lialf  the  length  of  the  blade, 
while  the  other  arise  some  distance  up  and  pass  nearly  or  quite  to  the 
apex ;  several  pairs  of  small  secondaries  arise  from  the  michib  in  the  extreme 
upper  part  of  the  blade;  ribs  with  occasional  branches  on  the  outside; 
ner\nlles  apparently  percurreut. 

This  species  is  represented  by  several  specimens,  3  of  the  best  of 
which  are  figured.  Unfortunately  none  of  the  specimens  are  perfect.  The 
larger  and  best-preserved  specimen  has  9  cm.  retained,  and  must  have 
been  11  or  12  cm.  in  length  when  complete.  This  specimen  is  4  cm.  wide. 
Another  example  has  7  cm.  of  the  ujiper  portion  preserved  and  is  about 
4.5  cm.  wide.  The  small  one  figured  is  not  quite  4  cm.  in  length  and 
about  1.5  cm.  in  width. 

Among  living  species  21.  Jamaren.sls  very  much  resembles  Tetranthera 
(Litsea)  dealhata  R.  Br.,  from  Australia,  and  also  approaches  Litsea  glauca 
Seib.,  from  Japan — that  is,  it  approaches  these  living  species  closely  enough 
t(^  make  it  certain  that  the  generic  reference  is  correct.  Among  the  fossil 
species,  Tetyaidhya  prcecursoria  Lx.,^  from  the  Bad  Lands  of  Dakota,  is  quite 
suggestive.  This  species  is  somewhat  obovate  instead  of  ovate-oblong,  and 
has  about  4  pairs  of  secondaries,  which  do  not  differ  in  size  as  they  do  in 
M.  lamarensis. 

Habitat:  East  1)ank  of  Lamar  River,  between  Cache  and  Calfee  creeks; 
collected  by  F.  H.  Knowlton,  August  21,  1888.  Yellowstone  River,  one- 
half  mile  below  mouth  of  Elk' Creek;  collected  by  F.  H.  Kjiowlton, 
August  27,  1888. 

Litsea  cuneata  n.  sp. 

PI.  XCII,  figs.  2-4. 

Leaf  membranaceous,  broadly  lanceolate,  wedge-shaped  at  base  and 
narrowed  in  about  the  same  manner  at  apex;  midrib  very  thick,  straight; 

'  Cret.  and  Tert.  Fl.,  p.  228,  PI.  XLVIII,  fig.  2. 


FOSSIL  FLORA.  727 

st'coiidiirics  at  ;i  very  acutt'  iinj;-l(',  crnsjjcdodrome,  alteninto,  lowor  pair 
tliiniu'st,  those  above  niiu-li  tliicker,  lininchino-  on  the  outside,  branches  at 
an  acute  angle,  craspedodronie;  intermediate  secondaries  several,  generally 
lost  in  the  space  l)etween  the  secondaries;  nervilles  strong-,  at  various 
angles,  mainly  percurrent;  finer  nervation  irregular. 

No  perfect  example  of  this  species  has  been  found,  thc^  fragments 
figured  being  all  that  we  have  to  represent  it.  The  specimen  showing  the 
wedge-shaped  base  is  only  5  cm.  long,  ])ut  was  probably  10  or  12  cm.  in 
length  when  perfect.  It  is  4  cm.  wide.  The  larger  of  the  others  is  the 
wedge-shaped  apical  portion,  and  is  6  cm.  long,  with  the  jwobability  of  its 
ha\-ing  been  at  least  12  cm.  long.  The  small  specimen  was  probably 
hardly  more  than  8  or  9  cm.  in  length  when  perfect.  The  upper  portion 
appears  to  have  more  numerous  secondaries  than  the  lower  jDart.  They  are 
also  branched  on  the  outside. 

Habitat:  Yellowstone  Eiver,  1  mile  below  the  mouth  of  Elk  Creek; 
collected  by  F.  H.  Kuowlton,  August,  1 888. 

CiNNAMOiiuM  spp:ctaj5ile  Hecr. 
n.  xciY,  tig.  (i. 

Cinnamomum  spectahile  Heer:  Fl.  Tert.  tielv..  Vol.  11,  p.  91,  PI.  XCVI,  figs.  1-8. 

The  leaf  figured,  whicli  appears  to  be  the  only  one  obtained,  differs 
slightly  from  the  figures  of  the  European  form  to  which  it  is  referred.  The 
lower  pair  of  secondaries,  for  example,  are  nearer  the  base  of  the  leaf  than 
in  the  figures  given  Ijy  Heer,  l)ut,  granting  the  slight  difterences,  I  have 
hesitated  to  make  it  a  new  species. 

Habitat:  Tower  Creek,  Yellowstone  National  Park;  collected  by 
Arnold  Hague  (field  No.,  103G),  August  16,  1883. 

PLATANACE.E. 

Platanus  guillelm.e  Gopp. 
PI.  XGVI,  tig.  1;  PI.  XCVII,  fig.  5. 

This  species  is  very  abundant,  being  represented  by  over  125  more  or 

less  perfect  specimens.     Some  of  these — as,  for  example,  the  one  figured 

are  particularly  perfect.  They  differ  somewhat  in  size,  the  average  being 
about  7  or  8  cm.  broad  between  the  lobes  and  8  or  9  cm.  in  leno-th  An 
occasional  one  is  14  cm.  broad  and  about  the  same  leng-th. 


728     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Tliese  leaves  agree  well  with  the  usual  description  and  ligures  of  this 
sjiecies,  especially  as  given  by  Lesquereux^  from  Carbon,  Wyoming. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  1, 
the  lowest  bed,  rare;  bed  No.  5,  rare;  bed  No.  6,  the  "  Platanus  bed," 
most  abundant  locality,  over  75  speciinens  noted;  bed  No.  7,  rare;  collected 
by  Lester  F.  Ward  and  F.  H.  Knowlton,  August,  1887.  Ea.st  end  of  Fossil 
Forest  Mountain,  middle  bed,  775  feet  above  valley  beloAv;  specimens  rare; 
collected  by  Ward  and  Knowlton,  August  13  and  22, 1887.  Specimen  Ridge, 
opposite  Slough  Creek,  I'are;  collected  b}'  Ward  and  Knowlton,  August, 
1887.  Hague's  Yellowstone  National  Park  collections  (field  No.,  1960), 
Fossil  Forest  section,  very  abundant;  collected  by  G.  M.  Wright  and  Walter 
H.  Weed,  September  20,  1885.  Hague's  YelloAvstone  National  Park  col- 
lections (field  No.,  1217),  Fossil  Forest  section,  upper  stratum;  collected  by 
Arnold  Hague,  September  24,  1884.  Hague's  Yellowstone  National  Park 
collections  (field  No.,  1219),  rare;  collected  by  Arnold  Hague,  September 
24,  1884.  South  end  of  Crescent  Hill,  6  feet  lielow  "Platanus  bed;" 
collected  by  F.  H.  Knowlton,  August  9,  1888. 

Platanus  Montana  n.  sp. 
PI.  XC'VI,  figs.  2,  3. 

Leaves  membranaceous,  somewhat  roughened,  rounded-oblong  in 
shape,  decurrent  on  the  petiole,  rounded  above  or  acuminate,  possibly 
slightly  3-y)ointed ;  margiu  simplj-  undulate  toothed ;  nervation  obscui'ely 
palmate ;  petiole  stout ;  midril)  thick,  straight ;  secondaries  several  (about 
6)  pairs,  the  k)west  some  distance  above  the  Ijase  of  the  Ijlade,  emerging  at 
an  angle  of  about  SC^,  passing  nearly  straight  to  the  border  and  ending  in  a 
small  marginal  tooth,  with  several  branches  on  the  outside  approximately 
at  right  angles  to  the  midrib  and  ending  in  marginal  teeth;  second  pair  of 
secondaries  strong,  arising  at  an  angle  of  45°,  nuich  arching  upward  and 
ending  either  in  the  margiu  or  possibly  in  short  lobes,  with  several  strong 
forking  branches  on  the  outside,  the  terminations  ending  in  the  teeth  ;  other 
secondaries  also  occasionalh'  forked  on  the  outside;  nervilles  strong,  occasion- 
ally pereurreut,  but  mainly  forked  or  broken;  finer  nervation  quadrangular. 

This  species  is  based  on  a  number  of  more  or  less  fragmentary  leaves, 
tlie    best    of  which    are  figured.      Tlie  most  perfect   specimen    is  12    cm. 

'Tert.  Fl.,  p.  183,  PI.  XXV,  figs.  1-3. 


FOSSIL  FLOKA.  729 

loiiji'  iiiid   altdut  10  vu\.  hrojid.      It  was  |irol)al)ly,  when  living-,  at  least  If) 
cm.  long-. 

The  marked  feature  of  this  leaf  is  that  it  is  not  strictly  palmately 
nerved,  having-,  as  pointed  out  in  the  diag-nosis,  the  2  lower  j)airs  of 
secondaries  with  branches  on  the  outside  which  end  in  tlie  niaro-iual  teeth 
Otlierwise  it  is  hardly  to  be  disting-uished  from  Philanus  rmjnoldsii  Newby., 
as  iig-ured  by  Lesquerenx'  from  the  Denver,  beds  of  Golden,  Colorado. 
This  species  was  described  by  Newberry-  as  having  the  margin  doubly 
serrate,  but  a  number  of  specimens  refen-ed  to  it  by  Lesquereux  have  the 
margin  undulate,  dentate,  or  even  entire.  Newberry's  type  had  3  lobes  or 
points  in  the  upper  portion,  while  certain  of  Lesquereux's  specimens  ^vere 
rounded  and  entire  above. 

The  smaller  leaves  from  the  lower  Yellowstone  described  by  Professor 
Ward  under  the  name  of  Grewiopsis  popuUfoJiu,^  especially  fig.  4  of  his  plate, 
approach  the  leaves  under  discussion.  These,  as  he  has  already  pointed 
out,  are  suggestive  of  P.  raynoldsU.     They  can  hardly  belong  to  Grewiopsis. 

Whether  the  leaves  from  the  Yellowstone  National  Park  should  be 
regarded  as  new  to  science  or  referred  to  Plotanus  raynoldsU  is  an  open 
question.  They  agree  closely  enough  in  size,  shape,  and  marginal  dentition, 
but  differ  in  the  nervation.  It  is  possible  that  this  character  may  be  of 
sufficient  importance  to  keep  them  distinct,  and  also  to  exclude  them  from 
the  genus  Platanus,  but  for  the  present  at  least,  and  until  better  material 
can  be  obtained,  they  may  remain  as  above. 

Habitat:  East  slope  of  high  hill  about  three-fourths  of  a  mile  south 
from  Yanceys;   collected  by  George  M.  Wright,  September  4,  1885. 

LEdlTMINOSiE. 

Acacia  macrosperma  n.  sp. 
PI.  XCVIII,  fig.  8. 

Legume  large,  more  than  8  cm.  long  and  2.2  cm.  wide,  broad  linear, 
possibly  constricted,  -with  obtuse,  regularly  rounded  end;  apparently  sur- 
rounded by  a  wing  5  nun.  broad;  seeds  numerous,  large,  oblono-,  10  mm 
long,  6  mm.  broad. 


'  Tert.  Fl,,  PI.  XXVI,  fig.  4 ;  PI.  XXVII,  figs.  1-3.   ' 
■^  Later  Ext.  Fl.,  p.  69;  111.  Cret.  .and  Tert.,  PI.  XVIII. 
»  Types  of  the  Laramie  Fl.,  p.  90,  PI.  XL,  figs.  3-5. 


730     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

This  species  appears  quite  unlike  any  species  Ijefore  found  in  America, 
but  is  not  greatly  unlike  A  DiicrojihijUa  Heer  from  the  Swiss  Tertiary.  The 
latter  species  is  not  quite  as  broad  as  A.  macrosperma,  and  has  not  the  end 
preserved.     The  seeds  are  about  the  same  size  in  both. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  7,  "Castanea  bed;"  collected 
l)y  Ward  and  Knowlton,  August  16-20,  1887. 

Acacia  lamarensis  n.  sp. 
PL  XOVllI,  tig.  (i. 

Legume  linear,  broad,  more  than  7  cm.  long,  and  1.7  cm.  Inroad;  end 
pointed;  apparently  with  marginal  wing  2  or  3  mm.  wide;  seeds  oval,  10 
nun.  long,  8  nun.  wide. 

This  may  jjossibly  be  the  same  as  A.  macrosperma,  but  it  appears  to 
differ  essentially  in  being  narrower  and  in  having  an  acuminate  instead  of 
an  obtuse  termination.  The  apparent  wing  and  the  seeds  are  much  the 
same  in  bt)th. 

Habitat:  Lamar  River,  between  Cache  and  Calfee  creeks;  collected  by 
Knowlton  and  Culver,  xlugust  21,  1888. 

Acacia,  wardii  n.  sp. 
PL  XGVIII,  tig.  7. 

Legume  narrow,  linear,  constricted,  (3  cm.  long,  9  mm.  wide  in  the 
broadest  portion  and  5  mm.  wide  at  the  constricted  point;  point  of  attach- 
ment reduced  to  a  slight  extension,  opposite  extremity  with  a  decided  curved 
beak;  seeds  apparently  present,  but  obscure. 

This  species  differs  markedly  from  the  others  just  described,  and  also,  so 
far  as  I  know,  from  any  heretofore  found. 

Haljitat:  Fossil  Forest  Ridge,  bed  No.  4,  "Aralia  bed;"  collected  by 
Ward  and  Knowlton,  August  16-20,  1887. 

Leguminosites  lesquereuxiana  Kn. 

PI.  LXXXIX,  tig.  4. 

Leiiiiminosites  lesquereuxiana  Kn.:  Bull.  U.  S.  Geol.  Surv.  No.  l.")2,  131,  1898, 
Leiiuminosites  vassioides  Lx.:  Tert.  Fl.,  p.  300,  PI.  LIX,  tigs.  l-i. 

Habitat:  Northeast  side  of  Crescent  Hill  opposite  small  jjond;  col- 
lected by  F.  H.  KnoAvlton  and  G.  E.  Culver,  August  2,  1888. 


FOSSIL  FLORA.  731 

LeGUMINOSITES    LAMAREXSIS  11.  sp. 
PL  LXXXIX,  figs.  5,  6. 

Leaflets  thin,  <)l)loiiji'-laii('e()l<ite,  voiinded-truneate  at  base,  long  acumi- 
nate at  apex;  midrib  stron<>-,  pcrt'i^etly  strai<>-ht;  seeoudaries  about  0  pairs, 
alternate,  at  an  angle  of  45°,  slightly  curving  upward;  remainder  of  nerva- 
tion not  retained. 

This  little  leaflet  is  6  cm.  in  length  and  17  mm.  in  width.  It  is  very 
regularl}-  rounded,  almost  truncate  at  base,  and  apparently  regularly  nar- 
rowed above  into  an  acuminate  apex.  The  petiole,  if  there  was  one,  is  not 
jireserved.  The  secondaries  are  alternate  and  camjjtodrome,  and  about 
8  or  9  pairs. 

The  nearest  related  species  is  Legmninosites  lesqiiereuxiana,^  from  the 
Green  River  beds  of  Green  River,  Wyoming,  and  also  Spring  Canyon, 
Montana.  This  differs  in  being  larger,  broader,  and  more  oblong-ovate 
than  the  one  under  discussion.  The  relationship  is  evidently  close,  and 
perhaps  more  material  would  show  closer  aflfinity  than  I  have  recognized. 

This  species  also  resembles  some  of  the  species  of  Leguminosites  from 
the  Tertiary  of  Switzerland,  as,  for  example,  L.  j)roserinn(B  Heei-.^  There 
can  be  no  question  as  to  the  correctness  of  the  refei'ence  to  this  genus. 

Habitat:  East  bank  of  Lamar  River,  between  Cache  and  Calfee  creeks; 
collected  by  F.  H.  Knowlton,  August,  1888. 

ANACARDIACE.E. 

Rhus  mixta?  Lx. 

Rims  mixta  Lx. :  Mem.  Mus.  Comp.  Zool.,  Vol.  VI,  No.  2,  p.  30,  PI.  IX,  fig.  13. 

A  single  small  and  somewhat  fragmentary  specimen.  It  resembles  the 
smaller  of  the  two  specimens  figured  by  Lesquereux. 

Habitat:  East  bank  of  Lamar  River,  between  Cache^and  Calfee  creeks; 
collected  by  F.  H.  Knowlton,  August  21,  1888. 


'Tert.  Fl.,  p.  300,  PI.  LIX,  egs.  1-4. 

^Tl.  Tert.  Helv.,  Vol.  Ill,  PI.  CXXXVIII,  figs.  50-55. 


732  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

CELASTRACE^. 

Celastrus  culveri  n.  sp. 
PI.  XCVII,  flg.  4. 

Leaves  membranaceous,  ovate-lanceolate,  apparently  rather  abruptly 
rounded  at  the  base,  but  gradually  narrowed  above  to  an  obtuseh'  acuminate 
apex;  inarg-hi  with  rather  remote,  small,  sharp,  outward-pointing  teeth; 
midrib  thick  below,  much  thinner  above;  secondaries  about  10  pairs,  alter- 
nate at  an  angle  of  35°  or  more,  much  curved  upward,  camptodrome 
very  near  the  margin,  with  branches  outside  entering  the  small,  weak  teeth; 
intermediate  secondaries  occasional,  thin,  disappearing  before  reaching  half 
the  distance  to  the  margin;  nervilles  percurrent;  finer  nervation  obscure. 

This  species  is  represented  b}-  2  well-preserved  leaves,  both,  unfor- 
tunately, representing  the  upper  portion  only.  The  longest  specimen  is 
10  cm.  in  length,  which  is  probably  not  far  from  its  original  full  length.  It 
is  a  little  over  5  cm.  broad  at  a  point  which  seems  to  be  some  distance 
below  the  middle.  Judging  from  the  contour  near  the  base,  it  seems  prob- 
able that  it  was  either  truncate  or,  possibly,  heart-shaped  at  base.  The 
teeth  of  the  margin  are  peculiar,  being  scattered,  small,  sharp,  and  outward 
pointing. 

This  species  appears  to  find  its  nearest  relative  in  some  described  fi-om 
the  Fort  Union  group  along  the  lower  Yellowstone.  Thus  it  resembles 
Celastrus  curvinervis  Ward^  in  shape  and  nervation,  but  difters  considerably 
in  size  and  wholly  in  the  teeth.  Celastrus  ovatus  Ward'-  has  somewhat  the 
same  shape,  but  difters  considerably  in  nervation  and  in  the  teeth.  Several 
of  the  other  species  described  by  Professor  Ward^  also  resemble  this  in 
one  or  more  particulars,  but  none  closely  enough  for  specific  identity. 

I  take  pleasure  in  naming  this  fine  species  in  honor  of  Prof.  G.  E. 
Culver,  who  assisted  in  collecting  at  this  place. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton  and  G.  E.  Culver, 
August,  1888. 

'Types  of  the  Laramie  Fl.,  p.  82,  PI.  XXXVI,  figs.  3,  4. 
^Op.  cit.,  p.  81,  PI.  XXXVI,  tig.  1. 
30p.  cit.,  Pl.XXXV. 


FOSSIL  FLORA.  *  733 

Celastrus  in^quahs  n.  sp. 
PI.  XCVIII,  fig.  3. 

Leaf  of  firm  texture,  ellii)tieiil-()bov;ito  in  outline,  stron<ily  unequal- 
sided,  rounded,  obtuse  above,  and  narrowed  lielow  into  an  apparently 
winged  j^t'tiole;  margin  strongly  sinuate-dentate  from  above  the  lower 
third  or  half  of  the  blade;  midrib  thin,  approximately  straight;  secondaries 
10  or  12  pairs,  lower  pairs  opposite,  others  alternate,  two  lower  pairs, 
and  about  6  secondaries  on  the  larger  side  of  the  blade  at  right  angles  to 
the  midrib,  those  on  narrow  side  of  blade  and  in  upper  portion  of  other 
side  from  right  angle  to  45°  or  more,  all  camptodrome,  arching  upward 
abruptly  near  the  margin  and  apparently  joining,  sending  branches  from 
the  outside  to  the  teeth  and  other  parts  of  the  margin;  nervilles  and  finer 
ner\-ation  obsolete. 

This  species,  as  exemplified  by  the  specimen  figured,  is  very  peculiar. 
It  is  7  cm.  long  and  a  little  more  than  4.5  cm.  wide.  It  is  abruptly  obtuse 
at  apex  and  appears  to  be  expanded  at  base  into  a  winged  petiole. 

The  margin  in  the  lower  portion  is  quite  entire,  while  above  it  is 
strongly  sinuate-toothed.  The  nervation  is  markedly  peculiar.  The  lower 
secondaries  are  at  right  angles  with  the  midrib,  as  are  several  more  on  the 
broader  margin,  while  those  on  the  narrow  side  of  the  blade  all  arise  at 
a  less  angle  and  curve  abruptly  near  the  margin.  Those  in  the  extreme 
tip  of  the  blade  cuj-ve  very  much  after  the  manner  of  Cornus.  All  send 
branches  from  the  outside  to  the  teeth.  The  finer  nervation  is  not 
preserved. 

This  species  is  wholly  unlike  any  with  which  I  am  familiar.  It 
possesses  the  character  described  by  Professor  Ward^  as  especially 
characteristic  of  the  American  fossil  forms  of  this  genus,  namely,  the 
arching  of  the  secondary  nerves  near  the  extremities,  with  short  subsidiary 
nerves  to  the  marginal  teeth.  Its  unequal-sidedness,  winged  petiole, 
and  sinuate  teeth  above  the  middle  of  the  blade  seem  to  still  further 
characterize  it. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  base  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

'  Types  of  the  Laramie  Fl.,  p.  78. 


734  GEOLOGY  OF  THE  YELLOWSTOls^E  NATIONAL  PARK. 

Celastrus  ellipticus  n.  sp. 

PI.  XCVII,  fig.  3. 

Leaf  of  firm  texture,  nearly  regularly  elliptical  in  outline,  abruptly 
rounded  above  to  an  obtuse  apex  and  below  to  an  almost  truncately  rounded 
base  which  is  slightly  decurrent  along  a  short  petiole;  margin  irregularly 
sinuate-toothed  from  a  short  distance  above  the  base;  midrilj  rather  thick, 
passing  straight  to  the  apex;  secondaries  about  15  pairs,  alternate  or  sub- 
opposite,  at  an  even  angle  of  about  35°,  straight;  distal  termination  of 
secondaries  unknown;  nervilles  and  finer  nervation  obsolete. 

This  perfect  leaf  is  7  cm.  long  and  4.;")  cm.  broad.  It  is  very  slightly 
unequal-sided,  the  difference  being,  however,  hardly  3  mm.  It  is  very  regu- 
larly elliptical,  with  a  sinuate  dentate  margin,  Avhich  begins  about  one-fourth 
the  length  of  the  leaf  from  the  base,  the  lower  portion  being  entire.  The 
nervation  is  very  regular,  consisting  of  about  15  pairs  of  secondaries,  which 
emerge  at  an  angle  of  about  85°  and  run  straight  toward  the  margin,  but 
tlie  manner  of  the  termination  at  the  margin  can  not  be  made  out,  from 
lack  of  preservation.     It  is  probable  that  they   arch  abruptly  near  the 

maro-iu  and  send  secondary  nervilles  to  the  teeth.     None  of  the  nervilles  or 

finer  nervation  can  be  made  out. 

It  is  possible  that  this  species  is  closely  related  to  C.  wteqiialis,  just 

described,  as  they  come  from  the  same  beds,  but  it  seems  hardly  proliable. 

This  latter  species,  as  already  pointed  out,  is  very  unequal-sided,  with  large 

sinuate  teeth,  and  peculiar  an-angement  of  secondaries.     C.  elUpHcus,  on  the 

other  hand,  is  almost  regular  in  shape,  has  twice  as  many  and  smaller 

sinuate  teeth,  and  regular  secondaries. 

This  species  does  not  approach  closely  to  any  described  species  of 

Celastrus  with  which  I  am  familiar. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 

Creek,  at  base  of  bluff;  collected  by  F.  H.  Knowltou,  August,  1888. 

El^odendron  polymorphum  Ward. 
PL  XCVII,  fig.  1. 

EUcodendron  2>olymorj)hum  Ward :  Types  of  tbe  Laramie  FL,  p.  84,  PL  XXXVIII, 
figs.  1-7. 

The  fine  specimen  figured  is  referred  with  some  doubt  to  this  species. 
It  has  much  the  same  shape,  serration,  and  type  of  nervation  as  jE.  jyoly- 


FOSSIL  FLOHA.  735 

morphum,  but  differs  in  being  imich  lai-ficer  and  in  liaving  more  nunierdiis 
and  c'l(»ser  secondaries.  It  is  undoubtedly  close  to  this  sj)ecies,  and  rather 
than  make  it  a  new  species  I  have  referred  it  to  this. 

Habitat:  Yancey  Fossil  Forest,  near  the  standing  trunks;  collected 
by  F.  H.  Knowlton,  August,  1H8.S. 

ACERACE^. 

Acer  vivarium  n.  sp. 
PI.  XCVIII,  tig.  4. 

Leaf  membranaceous,  palmately  3-lobed,  narrowed  below  to  a  wedge- 
shaped  base,  sinuses  rounded,  middle  lobe  lanceolate-acuminate,  as  long 
or  longer  than  the  body  of  the  blade  below  the  sinuses;  lateral  lobes 
at  an  acute  angle  (points  not  preserved);  margins  remotely  toothed  with 
small,  sharp,  upward-pointing  teeth;  midrib,  or  central  rib,  strong,  straight, 
slightly  stronger  than  the  lateral  ribs,  wdiich  arise  from  the  midrib  just 
above  the  base  of  the  blade  at  an  angle  of  about  70^  and  pass  up  straight 
to  the  points  of  the  lateral  lobes  or  curve  slightly  outward;  lateral  ribs 
with  several  pairs  of  secondar}-  branches,  those  on  the  outside  beginning 
just  above  the  base  of  the  blade  and  passing  straight  or  with  a  slight 
upward  cui've  to  or  entering  the  teeth;  secondaries  on  the  upper  or  inside, 
beginning-  below  the  sinus,  which  the  lowest  one  enters,  the  others  probably 
entering  the  teeth;  middle  lobe  with  about  6  pairs  of  alternate  second- 
aries arising  at  an  angle  of  70°  or  75°,  and  passing'  up  nearlj'  straight,  to 
end  in  the  teeth  or  fork  just  belo^^'  the  teeth,  one  branch  entering  and  the 
other  going  upward  near  the  margin  to  the  one  abo\-e;  ner^dlles  numerous, 
mainly  percurrent;  finer  nervation  beautifully  preserved,  forming  quad- 
rangular areolae. 

The  example  figured  is  the  only  one  observed  of  this  species.  It  is 
about  10  cm.  long  and  6  cm.  broad.  The  central  lobe  is  about  5  cm.  long 
and  a  little  more  than  2  cm.  wide.  The  lateral  lobes  appear  to  have  been 
about  2  cm.  wide  and  of  an  unknown  length. 

This  leaf  belongs  to  the  Acer  trilobatum  group,  so  many  forms  of  which 
were  described  by  Heer  from  the  Swiss  Tertiary.  In  shape  it  is  most  like  A. 
trUohatimi productwn,^  but  differs  in  having  only  very  small,  sharp  teeth.    It  is 

1  Fl.  Tert.,  Helv.,  Vol.  Ill,  PI.  CXV,  figs.  6-12. 


736  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

also  somewhat  like  A.  trilohatam  ir'wuspidatnm  Heer,  as  figured  by  Professor 
Ward  from  the  Fort  Union ^  gi'oup,  differing  in  being  much  more  wedge- 
shaped  at  base,  and  in  the  angle  of  the  lateral  ribs  and  secondaries. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  3,  "Magnolia  bed;"  collected 
by  Ward  and  Knowltou,  August,  1887. 

Acer,  fruit  of 
PL  XOVIII,  fig.  5. 

The  collection  coutaiias  several  of  these  fruits,  the  best  of  which  is 
figured.  While  they  are  very  definite  and  clearly  belong  to  Acer,  they  are 
not  usually  regarded  as  being  sufficiently  distinctive'  for  specific  reference. 
A  number  have  been  figured  and  named  also,  but  I  have  preferred  not  to 
name  these.  They  may  possibly  belong  to  the  preceding  species,  but  of 
this  there  is  no  proof. 

Habitat:  Crescent  Hill  above  Yanceys;  collected  by  W.  H.  Weed, 
September  28,  1885. 

SAPINDACEiE. 

Sapindus  affinis  Newby. 

PL  CII,  figs.  1-3. 

Sapindus  affinis  Newby, :  Later  Extinct  Floras,  p.  .31;  IlL  Cret.  aud  Tert.  PL,  PL  XXV, 
fig.  i. 

The  material  upon  which  this  determination  is  based  is  amjjle,  as  it 
consists  of  fully  100  specimens,  all  more  or  less  well  preserved.  These 
sjiecimens  differ  so  much  in  size  that  it  was  at  first  thought  that  at  least  2 
species  must  be  represented,  but  after  a  careful  study  it  has  been  found 
impossible  to  draw  any  satisfactory  line  between  them.  There  are  all 
gradations  of  size  from  the  little  slender  leaflets,  hardly  4  cm.  long,  to  the 
large  ones,  fully  10  cm.  long. 

In  the  only  published  figures  of  this  species  by  Newberry  the  nerva- 
tion is  not  shown,  but  the  National  Museum  contains  the  original  New- 
berry material,  and  on  studying  this  it  is  found  that  the  nervation  agrees 
perfectly  with  the  specimens  from  the  Yellowstone  National  Park.     It  may 

•  Types  of  the  Laramie  Fl.,  PI.  XXIX,  fig.  3. 


FOSSIL  FLORA.  737 

also  1)0  noted  that  Newberry's  material  does  not  show  the  leaflets  as  peti- 
oled,  but  in  the  description  of  S.  dj/inis  he  says,  "leaflets  *  *  *  sessile 
or  short-petioled."  Many  of  the  detached  leaflets  in  his  material,  named  in 
his  handwritnig,  are  distinctly  short-petioled,  in  which  particular  the  Park 
specimens  ao;i-ee.  Some  have,  it  is  true,  very  short  petioles,  yet  all  seem 
to  have  them. 

In  only  two  cases  have  leaflets  been  found  in  this  collection  attached 
to  the  rachis,  and  these  have  both  been  flg-ured. 

Habitat:  Yellowstone  Kiver,  one-half  mile  below  the  mouth  of  Elk 
Creek;  found  throughout  the  section,  and  most  abundant  at  the  bottom; 
collected  by  F.  H.  Kuowlton,  August,  1888. 

?  Sapindus  alatus  Ward. 
Sajnndus  alatus  Ward:  Types  of  the  Laramie  FL,  p.  6S,  PI.  XXXI,  figs.  3  4. 

This  specimen  is  the  only  one  that  I  venture  to  refer  to  this  species. 
It  was  found  in  the  same  beds  with  the  abundant  .S*.  affinis  Newby.,  and 
possibly  may  be  an  abnormal  or  unusual  leaflet  of  that  species.  It  is,  how- 
ever, more  regular,  and  has  the  thick  or  winged  petiole  of  S.  alatus. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  Yellowstone  National  Park;  top  of  bluff,  300  feet  above  the  river; 
collected  by  F.  H.  Knowlton,  August,  1888. 

Sapindus  grandifoliolus  Ward. 

PI.  XCIX,  tigs.  1,  2;  PI.  CII,  flg.  4. 

Sapindus  (jrandifoliQlus  Ward:  Types  of  the  Laramie  FI.,  p.  67,  P]   XXX   flffs  3-5- 
PI.  XXXI,  tigs.  1-2. 

Several  small  doubtful  leaves  are  referred  to  this  species.  One  in 
particular  has  some  resemblance  to  leaves  of  Juglans  rugosa  Lx.,  but  seems 
to  be  closer  to  the  Sapindus  grandiJoUolus  of  Ward. 

Habitat:  Fossil  Forest  Eidge,  bed  No.  6,  "Platanus  bed;"  collected 
by  Ward  and  Knowlton,  August,  1887.  Also  found  on  the  south  side  of 
Stinkingwater  Valley,  on  a  high  blufl"  east  of  mouth  of  Crag  Creek,  col- 
lected by  F;  P.  King  for  Arnold  Hague,  September  4,  1897. 

MON  XXXII,  PT  II 47 


738  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

SaPINDUS    GRANDIFOLIOLDIDES    11.  sp. 
PI.  C,  fig.  2. 

Leaflets  large,  of  firm  texture,  ovate-lanceolate,  unequal-sided,  rounded 
at  base  to  a  Avell-marked  winged  petiole,  apex  acute,  slightly  falcate; 
midrib  of  moderate  strength,  straight;  secondaries  about  7  or  8  pairs, 
strongly  alternate^  emerging  at  a  low  angle  and  soon  curving  up  and 
ijassins-  aloiiff  near  the  border;  the  secondaries  on  the  narrower  side  of 
the  leaflet  emerge  at  a  greater  angle  (30'^  to  45°)  than  on  the  opposite 
side;  finer  nervation  not  preserved. 

The  specimen  figured  is  absolutely  perfect  so  far  as  outline  and 
principal  nervation  go.  It  is  just  10  em.  long  and  3.7  cm.  wide  in  the 
broadest  portion,  which  is  a  little  below  the  middle.  The  margin  is 
slightly  undulate,  almost  toothed  in  one  part. 

This  species  so  closely  resembles  Sap'mdiis  (jrandifoJioJus  WaitP  from  the 
Fort  Union  group,  that  I  have  named  \i  grandifoUohkJes.  It  difters,  however, 
from  the  latter  in  lieiiig  more  markedly  iiijequilateral  and  in  having  a 
winged  petiole.     It  also  has  fewer  secondaries  than  S.  (jrandifoUolus. 

This  species  is  also  related  to  S.  oUusifoUus  Lx.,^  found  in  the  Fort 
Union  group.  From  this  it  differs  in  having  half  the  number  of  second- 
aries and  a  A\-inged  petiole,  otherwise  being  much  the  same. 

Professor  Ward's  S.  (dati(S^  from  the  same  place  as  S.  grandifoUolus  has 
a  winged  petiole,  but  difters  in  being  much  smaller  and  in  having  a  broken, 
loose  nervation.  It  is  possible,  however,  that  if  more  material  could  be 
obtained  it  could  be  referred  to  one  or  the  other  of  these  evidently  related 
forms. 

Habitat:  Northeast  side  of  hill  above  Lost  Creek,  bed  No.  1,  collected 
by  F.  H.  Knowlton,  August  8,  1888. 

Sapindus  wardii  11.  sp. 

PI.  XCVIII,  figs.  1,  2;  PI.  XCIX.  tig.  ,5. 

Leaflet  coriaceous,  broadl)'  lanceolate,  rounded  wedge-shaped  at  base, 
with  long  acuminate  falcate  apex;  margin  perfectlj"  entire;  midrib  thick. 


'  Types  of  the  Laramie  Fl.,  p.  67,  PI.  XXX,  figs.  3-5  (1887). 
=  Cret.  aud  Tert.  Fl.,  p.  23.5,  PI.  XLVIII,  figs.  5-7  (1883). 
30p.  cit.,  p.  68,  PI.  XXXI.  fig.  3,  4  (1887). 


FOSSIL  FLORA.  739 

passiiifi'  tliroui-li  tlu'  middle  of  tlu-  l)lii(le;  st'C'oiularies  about  8  pairs,  alter- 
nate, strongly  eainptodrome,  i'oriuiiig-  broad  loops  at  a  marked  distance 
from  the  margin,  occasionally  with  a  series  of  smaller  loops  outside;  inter- 
mediate secondaries  occasional;  nervilles  few,  percurrent;  finer  nervation 
forming-  large  quadrangular  meshes. 

The  specimens  figured  are  the  only  ones  observed  of  this  species.  The 
best  preserved  is  a  little  over  10  cm.  in  length  and  4  cm.  broad.  It  is 
marked  by  the  Lmg,  slender,  and  falcate  apex,  and  the  peculiar  looped 
secondaries,  which  are  joined  tar  inside  the  margin.  One  side  of  the  basal 
portion  of  the  leaflet  is  missing,  but  from  the  direction  of  the  secondaries 
it  is  probable  that  it  was  somewhat  unequal-sided. 

Fig.  1,  PI.  XOVIII,  Avhich  lacks  both  base  and  apex,  must  have  been 
at  least  13  cm.  in  length,  and  was  probably  longer.  The  other  (fig.  2,  PL 
XCVIII)  was  about  the  size  of  the  best-preserved  example. 

These  leaflets  very  closely  resemble  Fraxinus  affinis  Newby.,^  from 
Bridge  Creek,  Oregon.  This  has  the  same  type  of  nervation,  but  is  much 
smaller,  very  slightly  unequal-sided,  and  with  more  numerous  and  more 
regular  looped  secondaries.     The  finer  nervation  is  identical  in  each. 

There  is  some  doubt  as  to  the  correctness  of  the  reference  of  New- 
berry's leaf  to  the  genus  Fraxinus.  This  much  resembles  the  genus 
Sapindus  and  may  possibly  belong  to  it.  Sapindus  gramUfoUolm  Ward^ 
from  the  Fort  Union  group,  for  example,  has  much  resemblance  in  general 
character  to  these  leaves.  It  would  seem  that  they  should  all  be'' in  the 
same  genus.  However,  the  leaflet  under  consideration  is  undoubtedly 
closely  allied  to  what  Ward  has  called  Sapindus,  and  for  the  present  they 
may  remain  there. 

I  have  named  this  characteristic  species  in  honor  of  Prof  Lester  F. 
Ward,  who  was  present  when  it  Avas  collected. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  5;  collected  bv  Lester  F.  Ward 
and  F.  H.  Knowlton,  August  16-19,  1887.     Yellowstone  River,  one-half 
mde  below  mouth  of  Elk  Creek;   collected  by  F.  H.  Knowlton,  Auo-ust 
1888.  "  '        =      ' 


'  U.  S.  Nat.  Mus.,  Vol.  V,  1882,  p.  510;  Plates  (ined),  PI.  XLIX,  fig.  3. 
=  Types  of  tbe  Laramie  Fl.,  p.  67,  PI.  XXX,  figs.  4,  5. 


740  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

RHAMNACE.E. 

Rhamnus  rectinervis  Heer. 

Rhatnnus  rectinerris  Heer:  Fl.  Tert.  Helv.,  Vol.  Ill,  p.  SO,  PI.  CXXV,  figs.  2,  6.    Les- 
quereux:  Tert.  Fl.,  p.  279,  PI.  LII,  flgs.  12-15. 

This  species  was  first  detected  in  the  Park  by  Lesquerevix,^  and  the 
present  collection  contains  a  number  of  specimens  that  may  be  similarly 
referred.  They  are  all  entire,  in  which  respect  they  resemble  fig.  14  of 
Lesquereux's  plate  (loc.  cit.). 

Habitat:  Fossil  Forest  Ridge,  bed  No.  3,  "Magnoha  bed;"  bed  No.  7, 
"Castanea  bed;"  collected  by  Ward  and  Knowlton,  August,  1887. 

Paliurus  colombi  Heer. 
PI.  CI,  tig.  7. 
Paliurus  colombi  Heer.    Lesquereux:  Tert.  Fl.,  p.  273,  PI.  L,  flgs.  13-17  (1878). 

The  little  specimen  figured  appears  to  be  the  only  one  obtained  in  the 
area  under  discussion.  It  is  of  the  same  size  and  shape  as  many  of  the 
figures  of  this  species,  but  seems  to  difi"er  slightly  in  having  2  strong  sec- 
ondaries on  one  side  of  the  midrib!  It,  however,  approaches  certain  of  the 
figures  given  by  Heer"  of  arctic  examples  of  this  species. 

Habitat:  Head  of  Tower  Creek;  collected  by  W.  H.  Weed,  Septem- 
ber 25,  1885. 

ZlZYPHUS    SERRULATA    Ward. 
PI.  (JI,  figs.  4,  5. 

Ziziiphus  serrulata  Ward :  Types  of  the  Laramie  Fl.,  p.   73,  PI.  XXXIII,  figs.  3,  4 

(1887). 

The  two  figm-ed  examples  agree  very  closely  with  the  figures  given  by 
Professor  Ward.  They  both  have  teeth  well  marked,  and  tlms  agree  with 
fig.  4  (loc.  cit.).  .  They  are  not  quite  so  well  preserved  as  the  types,  and  do 
not  show  the  finer  nervation,  but  there  can  be  no  doubt  as  to  their  identity. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 


I  Hayden's  Anu.  Rept.,  1878,  Pt.  II,  p.  49. 
■^  Fl.  Foss  Arct.,  Vol.  I,  PI.  XIX,  tig.  3. 


FOSSIL  FLORA.  741 

yiTA(;p].E. 

CiSSUS    HAGUEI  U.  sp. 
PI.  GI,  fifi'.  2. 

Leaf  membranaceous,  qiia(lrau<>ular-ovate,  truncate  or  jjossibly  slig-litly 
heart-shaped  at  base  and  acuminate  at  apex,  Lateral  h)bes  sliort,  ol)tuse; 
margin  toothed,  the  teeth  ki\v,  obtuse  or  somewhat  acute;  nervation 
pahnate,  midrib  thin,  iierfectly  straight,  hiteral  ribs  of  same  strength  as 
midrib,  arising  at  an  angle  of  45°,  passing  directly  to  and  terminating 
in  the  obtuse  lateral  lobes;  ribs  with  4  or  5  branches  on  the  outside, 
which  terminate  in  marginal  teeth;  secondaries  about  4  pairs,  alternate, 
at  same  angle  as  the  ribs  and  terminating  in  the  teeth;  nervilles  thin, 
sparse,  percurrent  or  often  broken. 

This  fine  leaf  is  8.5  cm.  long,  5.2  cm.  broad  between  the  loljes  and  6.5 
cm.  broad  in  the  widest  part,  which  is  onh^  a  short  distance  above  the  base. 
In  outline  it  is  what  may  be  called  quadrangular-ovate — that  is,  between 
ovate  and  square.  It  is  palmately  3-ribbed,  the  lateral  ribs  being  at  an 
angle  of  about  45°  and  of  the  same  strength  as  the  midrib.  They  pass 
straight  to  and  terminate  in  the  sliort  lateral  lobes,  and  have  4  or  5  out- 
side branches  which  also  terminate  in  the  marginal  teeth. 

The  relation  of  this  species  is  undoubtedly  with  Cisms  ^mrroticefoUa 
Lx.,^  from  the  Green  River  group.  This  latter  species  differs  in  being 
relatively  longer,  without  especiallj'  marked  lateral  lobes,  with  larger,  more 
obtuse  teeth,  and  unforked  outer  branches  of  the  lateral  ribs.  There  are 
also  more  secondaries  in  the  upper  part  of  the  leaf.  These,  however,  are 
but  slight  differences,  and  are  possibly  only  such  as  might  be  expected  in 
individual  variation.  But  as  only  one  example  has  been  found  in  the 
Yellowstone  National  Park,  thei'e  is  no  means  of  knowing  what  maybe 
allowed  for  individual  variation,  so  I  have  preferred  to  keep  them  separate. 

I  take  pleasure  in  naming  this  species  in  honor  of  JMr.  Arnold  Hague, 
who  collected  it. 

Habitat:  Fossil  Forest  Ridge,  middle  stratum;  collected  by  Arnold 
Hague,  September  24,  1884. 

'  Tert.  Fl.,  p.  239,  PI.  XLII,  fig.  1. 


742  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

sterclliacej:. 

Pterospermites  haguei  n.  sp. 
PI.  XOIX,  flg.  4. 

Leaf  of  finn  texture,  broadly  oblong  in  outline,  slightly  iiifequilateral, 
truncate  at  base,  obtusely  pointed  at  apex;  margin,  except  at  base,  irregu- 
larly serrate,  the  teeth  small,  sharp,  upward  pointing;  midrib  strong, 
flexuose;  secondaries  6  pairs,  alternate,  at  an  angle  of  about  45°,  flexuose, 
craspedodrome,  or  subcamptodrome,  with  branches  outside  entering  the 
teeth;  lower  pair  of  secondaries  forming  a  series  of  broad  loops;  nei'villes 
strong,  mainly  broken;  finer  nervation  not  preserved. 

The  figured  specimen  of  this  species  is  11  cm.  long  and  nearly  7  cm. 
broad.  As  stated,  it  is  quite  regularly  broad-oblong  in  shape,  with  sparsely 
toothed  margins  except  near  the  base.  The  lower  pair  of  secondaries  form 
a  series  of  broad  loops,  while  the  upper  ones  are  mainly  craspedodrome. 

This  species  is  evidently  quite  closely  related  to  P.  minor  Ward^  from 
the  Fort  Union  group  near  the  mouth  of  the  Yellowstone.  Fig.  2  (loo.  cit.) 
is  especially  like  this  species,  but  differs  in  being  hardly  half  the  size  and 
in  being  markedly  heart-shaped  at  the  base.  It  perhaps  should  be  referred 
to  this  species  except  for  the  fact  that  the  other  2  leaves  included  by 
Professor  Ward  are  so  very  difi'erent  that  they  can  hardly  be  allied  to  the 
one  under  discussion. 

Habitat:  Fossil  Forest  Ridge;  collected  by  Arnold  Hague  (No.  1219). 

CKEDNERIACE.E. 

Credneria?  pachyphylla  n.  sp. 

PI.  CI,  tig.  0. 

Leaf  large,  thick,  round-ovate,  rounded  and  truncate  or  very  slightly 
hpart-shaped  at  base,  abruptly  acuminate  at  apex;  margin  apparently 
coarsely  sinuate-toothed;  petiole  long  (4.5  cm.),  thick  (4  mm.);  midrib 
thick,  passing  to  the  apex;  secondaries  6  or  7  pairs,  the  3  lower  pairs  (of 
which  the  very  lowest  is  slender  and  near  the  margin)  opposite  and  arising 
from  almost  the  same  })oint  at  the  base  of  the  blade,  others  alternate,  all 

1  Types  of  the  Laramie  Fl.,  p.  95,  PI.  XLII,  fig.  1-3. 


FOSSIL  FLORA.  743 

seemingly  craspedddroine,  occasionally  In-aiicliino-  iicnr  the  margin;  finer 
nervation  not  preserved. 

The  specimen  figured  is  the  only  one  that  has  lieen  found.  It  is  14 
cm.  long  without  the  petiole,  which  is  -il)  cm.  in  length.  Both  sides  of  the 
leaf  are  destroyed,  but  it  was  probably  about  10  cm.  wide. 

Habitat :  Yellowstone  River,  one-half  mile  below  mouth  of  Elk  Creek, 
bluff  about  40  feet  above  the  river ;  collected  by  F.  H.  Knowlton,  August 
27,  1888. 

TILIACEiE, 

TlLI.\    POPULIFOLIA    Lx. 

TiU<(  populi/olia  Lx.:  Cret.  and  Tert.  Fl.,  p.  179,  PI.  XXXIV,  figs.  S,  9. 

A  single  large,  fairly  well  preserved  .specimen  is  all  that  has  been 
found  of  this  species  It  is  referred  with  very  little  doubt  to  Lesquereux's 
species,  which  was  before  known  only  from  Florissant,  Colorado.  It  is  a 
little  less  heart-shaped  at  base  than  fig.  8  (loc.  cit.)  of  Lesquereux's  plate, 
but  in  the  discu-ssion  of  this  species  Lesquereux  describes  it  as  "round  or 
subcordate  at  base."  The  teeth  are  of  precisely  the  same  character,  being 
only  slightly  smaller.  The  thick  petiole  and  fine  palmate  nervation  are 
identical,  as  is  the  other  secondary  nervation. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August  27,  1888. 

GrEWIOPSIS  ■?    ALDERSONI    n.  sp. 

Leaves  of  .firm  texture,  broadly  obovate,  truncate  or  slightly  heart- 
shaped  at  base,  obtusely  acuminate  above;  margin  entire  at  base,  slightly 
undulate-toothed  above;  midrib  thick,  straight;  nervation  pinnate;  second- 
ai'ies  about  6.  pairs,  alternate,  at  an  angle  of  4.5°,  caniptodrome;  lowest 
pair  subopposite,  ari.sing  some  distance  above  the  base  of  the  blade,  with 
3  or  4  tertiary  branches  from  the  outside  which  are  camptodrome  and 
arch  well  inside  the  margin;  upper  secondaries  occasionally  forked  near 
the  margin;  nervilles  strong,  percurrent. 

I  refer  several  specimens  to  this  somewhat  doubtful  species.  Neither 
of  them  are  perfect,  but  as  far  as  can  be  made  out  the  average  length 
appears  to  have  been  about  9  cm.  and  the  width  about  6  cm. 

It  is  doubtful  if  these  leaves  belong  to  the  genus  Grewiopsis,  but  at 


744  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAllK. 

present  I  am  unable  to  suggest  a  closer  affinity.  They  have  the  same  size, 
shape,  and  approximately  the  same  nervation  as  G.  platanifoJia  Ward,^  from 
the  Fort  Union  group,  differing,  however,  in  not  having  a  toothed  margin. 
Professor  Ward  writes  that  the  specimen  upon  which  his  species  was 
founded  is  quite  obscure,  and  it  is  possible  that  they  may  really  be  nearer 
alike  than  appears  from  the  drawings.  Additional  material  is  needed  to 
tix  their  status. 

I  have  ventured  to  call  this  a  new  species,  and  have  named  it  in  honor 
of  Mr.  E.  C  Alderson,  who  accompanied  the  expedition  on  which  it  Avas 
obtained  and  assisted  in  making  the  collections. 

Habitat:  Specimen  Ridge,  opposite  mouth  of  Slough  Creek  and  near 
head  of  Crystal  Ci'eek;  collected  by  Ward  and  Knowlton,  August,  1887. 

ARALIACE/E. 

Aralia  wkightii  n.  sp. 
PL  01,  tig.  1. 

Leaf  firm,  coriaceous,  narrow  in  general  outline,  palmately  3  (possi 
bly  5)  lobed;  central  lobe  largest,  long,  ovate-lanceolate,  slender-pointed; 
lateral  lobes  slender-lanceolate,  half  the  length  of  the  central  lobe;  all 
margins  perfectly  entire ;  basal  portion  of  leaf  unknown ;  primary  nervation 
palmate;  middle  lobe  with  a  pair  of  opposite  nerves  nearly  at  right  angles 
to  the  midrib,  which  pass  to  the  sinus,  those  above  with  about  10  jiairs  of 
alternate  camptodrome  secondaries,  which  are  much  curved  upward  and 
arched  along  near  the  margin;  intermediate  secondaries  occasional;  lateral 
lobes  with  a  sti'ong  midrib  and  about  8  pairs  of  alternate  or  subopposite 
much-arched  camptodrome  secondaries;  finer  nervation  consisting  of  very 
fine  quadi-angular  areolation. 

This  very  peculiar  species  is  unfortunately  represented  by  only  the 
fragmentary  leaf  figured.  Tlie  basal  portion  is  entirely  destroyed  and 
it  is  therefore  impossible  to  determine  whether  there  were  5  or  only  3 
lobes.  There  is  some  evidence  in  favor  of  its  having  been  5-lobed.  The 
sinuses  separating  the  lobes  are  somewhat  rounded.  The  central  lobe  is 
very  much  the  larger.  From  the  sinus  it  has  6  cm.  preserved  and  must 
have  been  8  cm.  or  more  in  length  when  entire.     In  the  broadest  part. 


>  Types  of  the  Laramie  Fl.,  p.  89,  PI.  XL,  fig.  1. 


FOSSIL  FLORA.  745 

wliicli  is  al)out  one-fouith  of  its  loiigtli  fn)in  the  sinus,  it  is  2.5  cm.  broad. 
The  hiteral  htbes  are  about  3.5  cm.  long,  not  enlarged  upward.  At  base 
they  are  1  cm.  l)road,  from  whicli  point  the}-  taper  gradually  to  a  slender 
acuminate  apex.  The  nervation  has  been  described  in  the  diagnosis,  and 
may  also  be  clearly  made  out  from  tlie  e.xcellent  fio-ure. 

It  is  hardly  possible  to  compare  this  species  with  described  forms,  from 
the  fact  that  it  is  so  fragmentary  that  the  i)erfect  form  can  not  be  made 
out.  The  characters  of  the  larger  middle  lobe  and  the  ^-ery  much  smaller 
lateral  lobes  seem  to  be  so  marked  that  it  is  strongl)-  separated  from  any 
described  species.  Aralia  angustiloha  Lx.,'  from  the  Chalk  Bluffs  of  Cali- 
fornia, i)erliaps  is  closest  to  this  species,  yet  it  differs  markedly.  It  will  be 
necessary  to  wait  for  additional  inaterial  before  its  exact  character  can  be 
made  out. 

I  have  named  this  species  in  honor  of  Mr.  George  M.  AVright,  one  of 
the  collectors  of  this  and  many  other  valuable  specimeias  in  the  Yellowstone 
National  Park. 

Habitat:  Fossil  Forest  (No.  22c  of  section);  collected  by  "Wright  and 
Weed,  September  20,  1885. 

Aralia  notata  Lx. 
PL  C,  tig.  1. 

Aralia  notata  Lx.:  Tert.  FL,  p.  237,   PI.    XXXIX,  figs.  2-4.     Ward:  Types  of  the 

Laramie  FL,  p.  (iO,  PL  XXVII,  fig.  1. 
Flatanus  duhia  Lx. :  Hayiieu's  Auu.  Kept.  1873  (1874),  p.  40G. 

The  collection?,  contain  about  50  .specimens  that  evidently  belong  to 
this  species.  None  of  them  are  absolutely  perfect,  yet  the  general  character 
can  be  made  out.  They  come  from  three  localities,  one  of  wliich,  the 
Yellowstone  below  Elk  Creek,  was  given  as  a  type  locality  by  Lesquereux." 

There  appears  to  have  been  a  tendency  among  later  writers  to  regard 
this  as  the  same  as  Newberry's  PJatanus  nohilis^  from  the  Fort  Union  group, 
which  indeed  it  much  resembles.  They  were  both  very  large  species,  not 
often  preserved  entire,  but  they  seem  to  differ  essentially.  On  this  point 
Lesquereux  says:   "This  species  (A.  xotata)  seems  very  closely  allied  to 

'Mem.  Mus.  Comp.  Zocil.,  Vol.  VI,  No.  2,  PI.  V,  figs.  4,  5. 

''Tert.Fl.,  p.  237. 

^L.iter  Extinct  Flora,  p.  67. 


746     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAEK. 

Platamts  nobUls  Xewby.;  I  should  not  hesitate  to  consider  it  as  identical,  but 
for  the  cliaracter  of  the  lateral  nerves,  which  are  described  by  the  author  as 
straight,  and  terminating  in  the  teeth  of  the  margin.  In  this  species  the 
borders  are  entire  and  the  lateral  nerves  camptodrome.  The  difference  may 
be  merely  casual,  for  one  of  the  specimens  from  Troublesome  Creek  has 
the  close  secondarj^  veins  camptodrome  along  the  borders  of  the  inner  side 
of  the  lobes,  while  on  the  outer  side  the  borders  are  obscurely  cut  by  a 
few  sjnall  teeth,  into  which  the  veins  enter  as  craspedodrome.  C)ther  speci- 
mens, thus  of  Elk  and  Yellow  creeks,^  have  the  characters  of  F.  nobilis." 

It  would  thus  ajDpear  that  Lesquereux  himself  inclined  to  regard  the 
Park  specimens  as  being  referable  to  Platanus  nohUis,  Ijut  in  the  50  or  more 
specimens  that  I  have  studied  from  this  place  I  have  not  found  one  showing 
the  teeth  and  craspedodrome  nervation  of  P.  nohilis.  They  all  have  the 
distincth'  camptodrome  nerves,  as  shown  in  Lesquereux's  figures.  I  have 
therefore  decided  to  keep  theni  under  Aralia. 

The  further  question  of  the  correctness  of  this  generic  reference,  or 
rather  of  the  relation  of  thin  Ayalia  iiotafa  to  the  genus  Platanus,  will  not 
now  betaken  up.  Janko  has  said"  that  Platanus  nobilis  "non  est  Platanus," 
while  on  the  other  hand  Professor  Ward  has  suggested^  that  several  of  the 
so-called  species  of  Aralia  may  have  to  be  united  into  a  group,  under  the 
name  of  Protoplatanus,  representing  the  ancestors  of  Platanus.  A  small 
specimen  of  this  species,  obtained  by  Prof  J.  P.  Iddings  from  a  gulch  north- 
east of  the  peak  west  of  Dunraven,  is  exceptionally  well  preserved,  at  least 
as  regards  the  finer  nervation.  This  is  very  regularl)^  square,  being  only 
about  0.25  mm.  in  size.  The  leaf  appears  to  have  been  rather  thick,  possibly 
coriaceous. 

No  other  specimen  that  I  have  seen  has  this  finer  nervation  so  well 
preserved. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No. 
7,  "Castanea  bed",  about  25  specimens;  collected  by  Lester  F.  Ward 
and  F.  H.  Knowhon,  August  16-20,  1887.  Southeast  end  of  hill  above 
(north)  Lost  Creek,  bed  No.  4,  2  leaves;  collected  by  F.  H.  Knowlton, 
Au<>ust  8,  1SS8.     Yellowstone   River,  one-half  mile  below  mouth  of  Elk 


'  Probably  Elk  Creek  on  Yellowstone  River,     F.  H.  K. 
'Abstammuiifj;  il.  Platanen,  Englers  bot.  Jahrb.,  Vol.  XI,  1889,  p.  456. 
■T.v|)is  of  the  Laramie  Fl.,  j).  63. 


FOSSIL  FLOKA.  747 

Creek,  top  of  bluff;  collected  by  F.  IT  Knowltoii,  Au<>-ust27, 1888.  Ande- 
sitic  breccia,  near  <>-ulcli  northwest  of  peak  west  of  Dunraven;  collected  by 
J.  P.  Idding-s,  September  12,  18S3.  Also  found  on  Overlook  Mountain,  in 
breccia,  at  an  altitude  of  10,070  feet;  (collected  by  Arnold  Haf>-ue,  Aug-ust 
6,  1897.  Southern  spur  of  Chaos  Mountain,  at  an  altitude  of  10,100  feet; 
collected  by  Arnold  Hague,  August  11,  1897.  South  side  of  Stinkingwater 
Valley,  on  high  bluff  east  of  mouth  of  Crag  Creek;  collected  by  Arnold 
Hague,  September  4,  1807. 

Aralia  serkulata  n.  sp. 
PI.  CI,  fig.  3. 

Leaf  apparentl}'  subcoriaceous,  palmately  3-lobed,  middle  lobe  longest, 
ovate,  obtuse;  lateral  lobes  short,  pointing  upward;  borders  sharply  serru- 
late, with  small,  sharp,  upward-pointing  teeth;  secondaries  numerous,  close, 
alternate,  at  an  angle  of  25°  to  40°,  curving  upward  and  entering  the  teeth, 
or  sometimes  camptotli'ome  with  outside  branches  to  the  teeth,  usually  1 
tooth  between  the  2  entered  by  two  contiguous  secondaries,  which  is  sup- 
plied with  a  branch  from  the  middle  of  a  percurrent  nerville,  which  crosses 
just  below  it;  nervilles  numerous,  mainly  percurrent  and  approximately  at 
right  angles  to  the  secondaries;  finer  nervation  quadrangular. 

This  fine  and  apparently  characteristic  species  depends  upon  the  single 
example  figured.  It  lacks  the  entire  lower  portion  of  the  leaf,  but  2  lobes 
are  entirely  preserved,  and  a  large  portion  of  the  other.  The  central  lobe 
is  4.5  cm.  long  to  the  sinus,  and  the  lateral  one  about  1  cm.  higher  than  the 
sinus.     The  distance  between  the  lateral  lobes  is  8.5  cm. 

This  species  has  exactly  the  same  size  and  shape  as  many  of  the 
3-lobed  specimens  of  Aralia  notata  Lx.,^  foimd  in  the  same  beds. 

The  main  difference  is  in  the  sharply  serrate  margins,  the  teeth  extend- 
ing even  down  to  and  through  the  sinus,  and  in  the  secondaries  or  branches 
from  them  entering  the  teeth.  Occasionally,  as  indicated  under  the  diag- 
nosis, some  of  the  secondaries  are  camptodrome,  as  all  are  in  ^1.  notata,  with 
outside  branches  passing  to  the  teeth.  These  species  are  evidently  closely 
related  and  may  possibly  be  the  same,  although  probably  not,  for  in  100 
specimens  of  A.  notata  not  one  was  found  that  possessed  these  teeth. 

As  pointed  out  under  the  discussion  of  Aralia  notata  (see  ante,  p.  745), 


>Cf.  Lesquereux,  Tert.  Fl.,  PI.  XXXIX,  figs.  2,  3.     Ward;  Types  of  Laramie  Fl.,  PI.  XXVII,fig.  1. 


748     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

there  was  some  tendency  to  refer  it  to  Platanus  nobilis  Newby.,  which  is 
sometimes  slightly  toothed.  The  teeth  of  the  species  under  discussion  are 
distinctly  aralioid,  and  not  at  all  like  those  of  P.  vohilis. 

Aralia  serrulata  is  distantly  related  to  A.  digitata  Ward/  from  the 
Fort  Union  beds.  This  latter  sjjecies  is  3-lobed,  or,  more  often,  5-lobed, 
with  the  lobes  enlarged  upward,  and  serrate  with  shallow  teeth  only 
near  the  apex.  A.  macroi)liyUa  Newby.,'  from  the  Green  River  group  of 
Wyoming,  has  the  lobes  serrate,  but  the  teeth  are  large,  coarse,  and  often 
scattered,  and,  moreover,  the  leaf  is  twice  the  size  of  this  and  always 
S-lolied. 

A  number  of  species  of  Aralia  have  been  described  from  California, 
but  none  of  them  agree  Avith  A.  serrulata. 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluff;  collected  by  F.  H.  Knowlton,  August,  1888. 

Aealia  whitneyi  Lx. 

PI.  XCIX,  fig.  3. 

Aralia  whitneyi  Lx. :  Foss.  PI.  Aurif.  Gravels,  Mem.  Mus.  Comp.  Zool.,  Vol.  VI.,  No. 
li,  1878,  p.  20,  PL  V,  fig.  1.     Haydeu's  Aun.  Rept.  1878,  Pt.  II,  p.  W. 

This  fine  species  was  described  b}^  Lesquereux  from  the  Auriferous 
gravels  of  Chalk  Blutf,  Nevada  County,  California,  and  was  also  recognized 
by  him  in  material  collected  by  Mr.  W.  H.  Holmes  on  Fossil  Forest  Ridge' 
in  1878.  The  specimens  here  referred  to  this  species  come  from  probably 
the  same  locality  as  that  wliich  afforded  Holmes  material.  They  are,  with 
one  exception,  larger  leaves  than  described  in  the  type.  None  of  the 
specimens  are  perfect,  and  hence  it  is  difficult  to  determine  the  exact  size, 
but  they  must  have  been  15  to  20  cm.  long  and  probably  broader. 

The  small  specimen  mentioned  is  referred  with  some  hesitation  to  this 
species.  It  is  only  about  9  cm.  broad  and  7  cm.  long,  but  otherwise  hardly 
differs. 

Habitat:  Fossil  Forest  Ridge,  Yellowstone  National  Park,  bed  No.  4, 
"Ai-alia  bed,"  small  leaf  only;  bed  No.  7,  "Platanus  bed;"  Specimen 
Ridge,  Fossil  Forest,  opposite  Slough  Creek,  and  near  head  of  Crystal 
Creek,  "Platanus  bed;"  several  large  fine  leaves. 


I  Types  of  the  Laramie  Fl.,  p.  62,  PI.  XXVIII,  fig.  1. 

=  Proc.  U.  S.  Nat.  Mus.,  1882,  p.  513;  Plates  (iueil.),  PI.  LXVII,  fig.  1;  PI.  LXVIII,  fig.  1. 

'Cf.  Haydeu's  Anu.  Kept.,  1878,  Pt.  II,  p.  79. 


FOSSIL  FLORA.  741) 

Aralia  sp. 

This  tViifjinent  is  the  only  one  of  this  type  oljserveil,  and  is  too  ixior 
to  admit  of  satisfactory  identification  or  characterization  if  it  be  new.  It 
consists  of  a  portion  of  what  appears  to  be  the  central  lol)e  and  2  lateral 
lol)es  of  a  3-lobed  form.  The  sinnses  are  rounded  and  the  middle  lobe  is 
enlaro-ed  above,  with  the  marf^-ins  entire.  A  secondary  nerve  passes  up  to 
the  sinuses,  and  the  lobe  has  about  5  or  6  pairs  of  alternate  much  arched 
camptodrome  secondaries.     It  is  quite  unlike  any  other  form  observed,  so  far 

as  can  be  made  out. 

Habitat:  Hague's  Yellowstone  Park  collection,  Fossil  Forest  section. 
No.  22c;  collected  by  Wright  and  Weed,  September  20,  1885  (field  No., 

1959). 

CORNACEiE. 

CoKNUS  Newberryi  Hollick. 

PI.  cm,  fig.  6. 

Cormis  Newberryi  Hollick,  in  Knowltou:  Bull.  U.  S.  Geol.  Surv.  No.  152,  p.  77,  1898. 
Cornus  acuminata  Newby :  Later  Extinct  Floras,  etc.,  Ann.  Lye.  Nat.  Hist.  New  York, 
Vol.  IX,  1868,  p.  71;  111.  Cret.  and  Tert.  PL,  PI.  XX,  figs.  2-4;  Plates  (ined), 
PI.  XXXVII,  figs.  2-4. 

Represented  by  a  number  of  well-preserved  leaves,  agreeing  well  with 
NewbeiTy's  figures  and  description. 

Habitat:  Yellowstone  River,  one-half  mile  and  also  1  mile  below  mouth 
of  Elk  Creek,  at  top  of  bluff;  collected  by  F.  H.  Knowlton.  Also  found 
on  south  side  of  Stinkingwater  Valley  on  high  bluff  east  of  the  mouth  of 
Crag  Creek;  collected  by  Arnold  Hague,  September  4,  1897. 

Cornus  wrightii  n.  sp. 

PI.  cm,  figs.  4,  5. 

Leaves  of  firm  texture,  elliptical-lanceolate,  nan-owed  below  and 
apparently  slightly  decurrent,  rather  obtuse  at  apex;  margin  perfectly 
entire;  midrib  rather. thin,  slightly  flexuose;  secondaries  4  or  5  pairs,  lower 
pair  opposite,  others  alternate,  at  various  angles,  curving  along  the  margin 
and  in  the  upper  part,  turning  by  a  broad  bow  to  the  apex;  nervilles  few, 
approximately  at  right  angles  to  the  midrib;  finer  nervation  not  preserved. 


750  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Several  specimeus  of  this  interesting  species  are  known.  The  most 
perfect  one  is  figured,  and  is  7  cm.  in  length,  and  yet  lacks  a  small  portion 
of  both  base  and  apex.  It  is  a  little  more  than  2.5  cm.  broad.  It  is  quite 
regularly  elliptical-lanceolate  in  shape,  with  a  rounded,  rather  obtuse  apex 
and  a  more  narrowed  base.     The  secondaries  appear  to  be  luiiformly  of 

4  pairs,  those  in  the  upper  portion  of  the  leaf  arching  around  and  entering 
the  point. 

This  species  has  some  resemblance  to  tlie  preceding  species,  which 
differs,  however,  in  being  much  larger  and  in  having  an  acuminate  apex  and 
numerous  (8  or  9)  secondaries.     They  can  not  be  identical. 

It  differs  from  Cornus  ovalis  Lx.,^  from  Table  Mountain,  California,  in 
shape  and  nervation,  this  species  being  oval,  with  obtuse  base  and  apex. 

Among  living  species  this  has  considerable  afiinity  with  G.  imniculata 
I'Her.,  especially  with  cei'tain  of  the  narrow-leaved  forms. 

I  have  named  this  species  in  honor  of  Mr.  George  M.  Wriglit,  one  of 
the  collectors. 

Habitat:  Fossil  Forest  section,  Hague's  Yellowstone  Park  collection, 
No.  22c  of  section;   collected  by  Wright  and  Weed,  September  20,  1885. 

ERICACEiE. 

AeCTOSTAPHYLOS    ELLIPTICA   U.  Sp. 
PI.  XCVII,  lig.  2. 

Leaf  very  thick,  leathery;  elliptical  in  shape,  obtuse  above,  slightly 
wedge-shaped  at  base;    midrib  thick,  slightly  flexous;   secondaries  about 

5  pairs,  alternate,  lower  ones  short,  at  a  low  angle,  upper  ones  at  an  angle 
of  about  45°,  soon  curving  upward  and  arching  about  near  the  margin  to 
join  the  one  next  above;  nervilles  strong,  percurrent;  finer  nervation 
obsolete. 

This  fine  little  leaf  is  almost  perfect.  It  is  4.5  cm.  in  length  and  1 8  mm. 
in  width.  The  petiole  is  about  3  mm.  long  and  is  ver}'  thick,  as  is  the 
flexuous  midrib.  The  secondaries  are  also  strong,  the  upper  ones  arching 
and  joining  in  the  upper  part  of  the  leaf 

This  leaf  is  very  thick,  showing  that  it  was  of  firm,  leathery  texture. 
It  is  e\'idently  related  to  the  bearberry  {Arctostaphjlos  uva-ursi)  in  shape, 


'  Mem.  MuB.  Comp.  Zool.,  Vol.  VI,  No.  1,  p.  23,  PI.  VI,  tigs.  1,  2. 


FOSSIL  FLORA.  751 

texture  of  the  leaf,  and  nervation.      Tt  ditfers  in  l)Hin<i'  almost  twice  the  f^ize 
of  the  livin<>-  form  and  in  having-  coarse  nervation.      It  has  also  a  short  petiole. 
Habitat:   Yellowstone  Uiver,  one-half  mile  helow  mouth  of  Elk  Creek; 
collected  by  F.  II.  Knowlton. 

EBEXACE.E. 

DiOSPYROS    HKACHYSEPALA    Al.  Br. 

J)iosp!/ri)s  hrachysepala  Al.  Br.     Ward:  Types  of  the  Laramie  Fl.,  p.  104,  PI.  XLIX, 
figs.  1,  -2. 

A  tinely  preserved  leaf,  almost  identically  the  same  as  Ward's  fig.  2, 
except  that  the  secondaries  are  a  little  closer  together. 

Habitat:  Fossil  Forest  Ridge,  bed  No.  4,  "Araliabed;"  collected  b}' 
Ward  and  Knowlton,  August,  1887. 

DlOSPYRO.'^  LAMARENSIS  n.  sp. 
PI.  XCV,  tigs,  o,  6;  PL  XCVI,  tig.  4. 

Leaf  membranaceous,  regularly  elliptical  or  ovate-elliptical,  equally 
rounded  at  base  and  apex,  or  slightly  broader  at  base;  petiole  not  preserved, 
apparently  with  a  slight  wing;  midrib  thin,  straight;  secondaries  7  or  8 
pairs,  alternate,  thin,  camptodrome,  arising  at  an  angle  of  45°  or  50°,  pass- 
ing straight  toward  the  borders,  near  which  they  arch  and  join  by  loops  to 
the  secondary  next  above;  intermediate  secondaries  occasional,  thin,  usually 
joining  the  secondary  next  below;  finer  nervation  consisting  of  numerous 
irregular  nervilles,  jiroducing  irregularly  quadrangular  areola?. 

This  species  is  about  5  cm.  long  and  a  little  more  than  3  cm.  wide,  and 
is  quite  regularly  elliptical  in  shape.  As  stated,  the  petiole  is  not  preserved, 
but  judging  from  the  base  of  the  blade  it  seems  probable  that  it  Avas 
slightly  winged.  The  lower  pair  of  secondaries  arise  from  the  very  base  of 
the  blade  and  are  very  thin;  the  others  are  all  alternate  and  camptodrome. 
One  of  the  other  leaves  figured  is  approximately  of  the  same  shape,  but 
has  slightly  more  indication  of  having  had  a  winged  petiole.  It  is  rounded 
at  base  and  has  a  loose  nervation,  as  in  the  other. 

This  species  is  closely  related  and  possiblj-  identical  with  Diospyros 
".opeana  Lx.,^  from  Florissant,  Colorado.     This  latter  sjjecies  differs  in  being 


'Tert.  Fl.,  p.  232,  PI.  XL,  fig.  11;  Cret.  .-inil  Tert.  Fl.,  p.  175,  PI.  XXXIV,  fig.  3. 


752     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

more  or  less  distinctly  wedge-sliaped  at  base,  and  is  obovate  rather  than 
elliptical  in  shape.     The  nervation  is  similar  in  both. 

I),  lamarensis  is  also  like  certain  leaves  of  B.  hrachysepala  Al.  Br.,  from 
Florissant  and  the  Fort  Union  group  of  Montana.^  The  leavesj  from  the 
Fort  Union  group  are  rather  larger,  and  have  the  secondaries  at  a  different 
angle  and  are  without  the  peculiar  finer  nervation.  It  seems  best,  however, 
to  keep  them  distinct,  at  least  for  the  present. 

Hal^tat:  Lamar  River,  between  Cache  and  Calfee  creeks;  collected  by 
F.  H.  Knowlton,  August,  1888.  Fossil  Forest;  collected  by  Arnold  Hague, 
September  24,  1884. 

DiOSPYKOS    HAGUEI  n.  Sp. 
PI.  G,  flg.  3. 

Leaf  coriaceous,  elhptical,  entire,  obtuse  at  apex  and  base;  petiole 
tliick;  midrib  thick,  flexuose;  secondaries  about  6  pairs,  alternate,  very 
irregular,  the  pair  at  the  base  of  the  blade  thin,  vanishing  near  the  margin, 
next  pair  strongest,  passing  to  the  upper  part,  camptodrome,  branching 
on  the  outside  and  forming  broad  loops  well  inside  the  margin;  upper 
secondaries  smaller,  camptodrome,  forming  broad  loops;  nervilles  sparse, 
strong,  percurrent ;  finer  nervation  obsolete. 

This  species  rests  on  the  tine,  nearly  perfect  leaf  figured.  It  is  7  cm. 
long,  including  the  petiole,  which  is  1 4  nmi.  long  and  2  nun  thick.  The 
blade  is  nearly  regularly  elliptical  in  shape  and  3.3  cm.  broad.  The  nerva- 
tion is  peculiar,  as  may  be  drawn  from  the  description  and  figure.  All  of  the 
secondaries  except  the  lower  pair  are  camptodrome,  forming  by  union  Avith 
the  one  next  above  a  series  of  broad  loops  some  distance  inside  the  margin. 

This  type  of  nervation  is  peculiar  and  is  clearly  that  of  Diospyros.  It 
approaches  quite  closely  to  certain  small-leaved  forms  of  D.  virginiana  L. 
Among  fossil  forms  it  somewhat  resembles  Diospyros  ohtusa  Ward,^  from 
Sevenmile  Creek,  Montana,  in  the  Fort  Union  group.  The  latter  species 
is  of  approximately  the  same  size  and  shape,  but  differs  in  the  details  of 
nervation.     It  is,  however,  quite  close. 

I  have  named  this  species  in  honor  of  Mr.  Arnold  Hague,  of  the  United 
States  Geological  Survey. 

'Cf.  Lesquereux  Cret.  ami  Tert.  Fl.,  PI.  XXXIV,  fig.  1,  2;  Ward,  Types  of  the  Laramie  Fl., 
PI.  XLIX,  fig.  1,2. 

■  Types  of  the  I.aramie  Fl.,  p.  105,  PI.  XLIX,  fig.  5. 


FOSSIL  FLORA,  753 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  base  of  blut!";  collected  by  F.  H.  Ivuowlton,  Augu.st,  1888. 

OLEACEiE. 

—  Fraxinus  WKiGHTii  n.  sp. 

PL  XC,  fig.  4. 

Leaflet  small,  membranaceous  in  texture,  oblong  in  outline,  unequal- 
sided,  wedge-shaped  at  base,  obtuse  at  apex;  margin  with  few  irregular 
scarcely  pointed  teeth;  midrib  strong,  slightly  flexuose;  secondaries  about 
7  pairs,  alternate,  at  various  angles,  flexuose,  camptodrome  or  subcras- 
pedodrome,  mostly  arching  and  joining  by  bows  some  distance  inside  the 
margin,  sometimes  entering  the  teeth,  and  usually  with  outside  branches 
to  the  minute,  often  obtuse,  teeth;  nervilles  numerous,  irregular,  all  forked 
or  broken ;  finer  nervation  producing  irregular  quadrangular  meshes. 

The  specimen  figured,  which  was  the  only  one  found,  is  4  em.  long 
and  2.2  cm.  wide.  It  is  decidedly  inasquilateral,  with  a  wedge-shaped  base, 
and  undulate-toothed  margin.  The  nervation  is  camptodrome,  with  the 
secondaries  arched  and  joined  by  broad  bows  well  inside  the  margin,  or 
occasionally  with  a  secondary  entering  a  tooth,  thus  becoming  craspedo- 
drome.  The  finer  nervation  is  beautifully  preserved,  producing  very 
irregularly  quadrangular  jneshes 

The  relation  of  this  species  is  undoubtedly  with  Fraxinus  heerii  Lx.,^ 
from  Florissant,  Colorado.  Lesquereux's  species  differs  in  being  much 
larger  and  narrower,  with  merely  undulate  margin.  The  nervation  is 
strictly  camptodrome,  but  otherwise  identical. 

I  have  named  the  species  in  honor  of  Mr.  George  M.  Wright,  by  whom 
it  was  collected. 

Habitat:  Yellowstone  River,  below  Elk  Creek,  top  of  bluff";  collected 
by  Greorge  M.  Wright,  September  9,  1885., 

Phyllites  crassikolia  n.  sp. 
PI.  CII,  fig.  5;  PI.  cm,  fig.  1. 

Leaves  very  large,  thick,  apparently  radely  oval  or  orbicular  in  out- 
line ;  base  rounded  or  slightly  heart-shaped,  upper  portion  rounded  (?);  margin 


•  Cret.  and  Tert.  Fl.,  p.  169,  PI.  XXXIII,  figs.  5,  6. 
HON  XXXII,  PT  II 48 


754  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAlfK. 

entire  or  undulate  ;  petiole  usually  ver}'  thick  (7  mm.  in  diameter) ;  midrib 
thick  (5  mm.),  straight,  splitting  above  into  2  equal  branches;  secondaries 
thick,  straight,  alternate  or  subopposite,  often  forking,  craspedodrome  or 
subcamptodrome,  the  secondaries  or  their  branches  united  by  broad  loops 
with  branches  from  the  outside  to  the  margin;  nervilles  very  numerous, 
strong,  mainly  percurrent,  yet  often  forked  or  broken;  finer  nervation,  pro- 
ducing large,  mahdy  irregular,  quadrangular  areolse. 

This  species  is  based  on  a  number  of  fragments  that  are  insufficient  to 
show  the  true  character.  Two  of  the  largest  are  figured,  showing  what  is 
assumed  to  be  the  base  and  upper  portions.  The  largest  is  13  cm.  long  and 
about  10  cm.  wide,  but  this  could  have  been  only  a  fragment  of  the  original 
size.  This  specimen  (fig.  6  of  PI.  CII)  is  peculiar  in  that  the  midrib  splits  in 
the  upper  ])ortion  into  2  equal  branches,  both  of  which  are  again  branched 
on  the  outside.  This  leaf  appears  also  to  have  been  2-lobed  at  the  apex, 
all  of  which  may  be  abnormal  and  due  to  an  injurj^  to  the  midrib.  The 
nervation  in  the  uj)j)er  portion  quite  markedly  camptodrome. 

The  lower  portion  that  I  have  assumed  to  belong  to  this  species  has  an 
exceedingly  thick  i)etiole,  of  which  only  a  fragment  is  preserved,  and  also 
a  thick  midril).  They  appear  so  different  that  it  seems  hardly  probable 
that  they  can  be  identical,  but  rather  than  multiply  unsatisfactory  species 
they  may  remain  as  above  until  additional  material  can  be  obtained.  None 
of  the  margin  except  the  very  base  is  preserved. 

On  account  of  the  fragmentary  nature  of  these  leaves,  I  am  unable  to 
determine  with  satisfaction  the  proper  genus  to  which  they  should  be 
referred.  In  this  uncertaint}'  I  have  placed  them  provisionally  under 
Phyllites. 

Habitat:  Cliff  on  west  end  of  Fossil  Forest  Ridge;  Fossil  Forest  Ridge, 
near  head  of  Crystal  Creek,  various  beds;  collected  by  Ward  and  Knowl- 
ton,  August,  1887,  and  by  W.  H.  Weed,  September  20,  1885. 

Carpouthes  orseus  Lx. 
Carpolithes  ossem  Lx.:  Ann.  Kept.  U.  S.  Geol.  and  Geo^-.  Surv.  Terr.,  404, 1872  (1873). 

A  very  doubtful  species,  of  wliich  the  type  is  lost  and  the  species 
not  since  obtained. 

Habitat:  "Elk  Creek,  near  Yellowstone  River;  A.  C  Peale,  Joseph 
Savage,  and  O.  C.  Sloane." 


l-'OSSIL  FLORA.  755 

CaKPITES    I'EOUNCULATUS    11.  sp 

PI.  cm,  fig.  3. 

Fruit  round,  apparently  4  or  5  celled;  pedicel  sliort,  tliick. 

This  fragmentary  fruit  is  hardly  worthy  of  description,  for  it  nun'  he 
so  deformed  by  pressure  that  it  can  not  be  recognized  again. 

Among  the  described  fruits  of  this  heterogeneous  class  C.  viburni  Lx.,' 
from  Black  Buttes,  Wyoming,  is  perhaps  closest,  but  proljablv  the  resem- 
blance is  onlv  superficial 

Habitat:  Yellowstone  River,  one-half  mile  below  the  mouth  of  Elk 
Creek,  top  of  bluif  (with  Ulmus  fruits);  collected  by  F.  H.  Kuowlton, 
August,  1888. 

FOSSIL  FORESTS. 

The  fossil  forests  of  the  Yellowstone  National  Park  are,  be3"ond 
question,  the  most  remarkable  of  their  kind  that  have  thus  far  been  dis- 
covered in  any  part  of  the  world.  Isolated  jiieces  or  stumps  of  fossil  wood 
are  of  common  occun-euce,  being  found  in  almost  all  quarters  of  the  globe, 
from  near  the  point  farthest  north  that  was  reached  b}'  the  Greely  Ai'ctic 
Expedition  to  southern  South  America ;  from  Spitzbergen  and  Nova  Zembla 
to  South  Africa  and  Australia,  and  geologically  from  the  Devonian  to  beds 
in  process  of  formation  at  the  present  da}'.  lu  many  localities  there  are 
aggregations  of  logs  and  stumps  that  are  worthy  to  be  dignified  by  the 
name  of  fossil  forests;  as,  for  example,  in  Chalcedony  Park,  near  Holbrook, 
Arizona;  near  Calistogu,  California,  and  in  the  vicinit}-  of  Cairo,  Egypt. 
But  in  all  of  these  places,  so  far  as  known,  all  or  most  of  the  trunks  are 
prostrated  and  lie  scattered  about  in  the  greatest  confusion.  In  some  cases 
there  is  evidence  that  the  logs  Avere  transported  by  currents  before  being  fos- 
silized. The  fossil  forests  of  the  Yellowstone  National  Park  and  vicinity,  on 
the  other  hand,  are  not  only  more  extensive  in  area,  but  the  trees  are  almost 
all  standing  upright  in  the  exact  positions  in  which  the}'  grew  originallv. 
Many  of  these  trunks,  standing  on  the  slopes  and  steeper  hillsides,  rise  to  a 
height  of  20  or  30  feet,  and  are  covered  with  lichens  and  blackened  and 
discolored  by  frost  and  rain.  At  a  short  distance  it  is  hard  to  distinguish 
them  fi'om  the  near-by  living  relatives.     The  following  account  bv  Prof 


'Tert.  Fl.,  p.  305,  PI.  LX,  fig.  26. 


756  GEOLOGY  OF  THE  YELLOVVSTOXE  NATIONAL  PARK. 

W.  H.  Holmes,  the  discoverer  of  these  fossil  forests,  shows  the  impression 
first  made  by  the  siglit  of  them : 

As  we  ride  up  the  trail  that  meauders  the  smooth  river  bottom,  we  have  but 
to  turu  our  attention  to  the  cliU's  ou  the  right  hand  to  discover  a  multitude  of  the 
bleached  trunks  of  the  ancient  forests.  In  the  steeper  middle  portion  of  the  moun- 
tain face,  rows  of  upright  trunks  stand  out  on  the  ledges  like  the  columns  of  a  ruined 
temple.  On  the  more  gentle  slopes,  farther  down,  but  where  it  is  still  too  steep  to 
support  vegetation,  save  a  few  pines,  the  petrified  trunks  fairly  cover  the  surface, 
and  were  at  first  supposed  by  us  to  be  the  shattered  remains  of  a  recent  forest.' 

Fossil  trees  or  fragments  of  wood  of  gi'eater  or  less  size  are  found  in 
many  parts  of  the  Park,  hut  their  distribution  is  mainly  confined  to  the 
northern  and  northeastern  portions.  The  forests  of  standing  trees  are  all 
found  in  the  vicinity  of  the  Lamar  River,  the  most  striking  being  exposed 
on  the  slopes  and  cliffs  of  Amethyst  Mountain  and  Specimen  Ridge.  Nearly 
all  of  these  forests  are  easily  accessible  from  the  well-traveled  road  between 
the  Mammoth  Hot  Springs  and  the  town  of  Cooke,  Montana. 

As  the  visitor  enters  the  area  drained  by  the  Lamar  River  and  by 
the  smaller  streams  running  into  the  Yellowstone  below  the  Grand  Canyon, 
evidences  of  proximity  to  the  fossil  forests  are  soon  at  hand.  In  the  bed 
"of  every  stream  pieces  of  wood,  often  of  considerable  size,  may  be  found. 
These  pieces  have  in  many  cases  been  carried  miles  from  their  original 
source  by  the  torrents  incident  to  the  melting  of  the  snows  in  spring.  In 
this  way  the  pieces  of  wood  have  become  rounded  and  worn  and  at  remote 
distances  are  changed  into  smooth,  rounded  pebbles. 

The  first  forest  to  be  visited  is  near  Yanceys,  and  is  known  as  Yanceys 
Fossil  Forest.  It  is  located  about  1  mile  south  of  the  hotel,  on  the  middle 
slope  of  a  hill  that  rises  about  1,000  feet  above  the  little  valley.  It  is 
reached  by  an  easy  trail,  and  as  one  approaches,  a  number  of  trunks  are 
observed  standing  upright  among  the  stumps  and  trunks  of  living  trees, 
and  so  much  resembling  them  that  a  near  view  is  necessary  to  convince  the 
visitor  that  they  are  really  fossil  trunks.  Only  two  rise  to  a  considerable 
height  above  the  surface.  The  larger  one  is  about  15  feet  high  and  13  feet 
in  circumference;  the  other  is  a  little  smaller.  The  roots  are  not  exposed, 
so  that  it  is  impossible  to  determine  the  position  of  the  part  in  view.  Its 
original  length  can  not,  of  course,  be  ascei'tained.     It  is  also  impossible  to 

'  U.  S.  Geol.  and  Geog.  Survey  of  the  Terr.,  Hayden's  Twelfth  Anuiial  Report,  1878  (1883),  p.  48. 


FOSSIL  FLOKA.  757 

determine  the  original  (liain(;ter,  as  the  bark  is  in  no  case  preserved.  The 
standing  trees  are  both  conifers,  and  belong  to  the  genus  Cupressinoxylon. 

Above  these  standing  trunks  many  others  are  visible,  but  the  disinte- 
grating forces  of  nature  keep  them  at  about  the  same  level  as  that  of  the 
surrounding  rock,  from  the  fact  that  they  tend  to  break  up  easily  into  small 
fragments.  Some  of  these  trunks  rise  only  a  few  inches,  while  others  ai-e 
nearly  covered  by  the  shifting  debris.  They  vary  in  size  from  1  to  4  feet 
in  diameter,  and  are  so  perfectly  preserved  that  the  annual  rings  can  be 
easily  counted.  The  internal  structiu'e  is  also  in  most  cases  nearly  as 
perfect  as  though  the  tree  were  living.  The  cells  still  retain  their  delicate 
markings,  and  often  their  perfect  form. 

There  are  numerous  fossil  leaves  found  in  the  rocks  about  the  bases  of 
these  trees,  but  none  apparently  corresponding  to  the  ti-unks;  that  is,  the 
trunks  are  all  coniferous,  while  the  leaves  are  dicotyledonous;  but  from  the 
nature  of  the  case  a  coniferous  trunk  is  much  more  readily  preserved  than 
a  dicotyledonous  one. 

The  next  forest  that  claims  attention  is  the  one  mentioned  by  Mr. 
Holmes,  and  is  the  one  most  frequently  visited  by  observers.  It  is  known 
locally  as  the  Fossil  Forest,  and  is  exposed  on  the  northern  slope  of  Amethyst 
Mountain,  opposite  the  mouth  of  Soda  Butte  Creek.  The  trunks  may  be 
easily  seen  from  the  road  along  the  Lamar  River  and  quite  a  mile  away. 
They  stand  upright — as  Holmes  has  said,  like  the  pillars  of  some  ancient 
temple — and  a  closer  view  shows  that  there  is  a  succession  of  these  forests, 
one  above  the  other,  through  the  entire  2,000  feet  of  this  mountain.  That 
is  to  say,  in  early  Tertiary  time  a  magnificent  forest  flourished  in  this  region, 
which  was  buried  under  the  dtjbris  ejected  from  volcanoes  of  greater  or 
less  size  that  are  supposed  to  have  existed  in  this  vicinity.  The  trees  were 
suiTounded  by  silica-charged  waters  and  were  turned  to  stone.  The  area 
on  which  they  gi'ew  was  probably  undergoing  a  very  gradual  submergence 
and  the  trees  were  slowly  entombed.  This  is  shown  by  the  fact  that  the 
trees  are  in  an  upright  position  and  were  not  broken  by  the  incoming- 
material  which  covered  them. 

After  the  first  forest  was  entombed,  quiet  was  restored  for  a  sufficient 
length  of  time  for  a  second  forest  to  grow  above  it.  Then  volcanic  acti^dty 
was  renewed,  and  the  second  forest  was  buried  and  silicified  as  the  first  had 
been.     This  process  was  repeated  until  2,000  feet  of  volcanic  material  had 


758     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

been  accumulated  ami  not  fewer  than  fifteen  forests  were  entombed.  Then 
the  volcanoes  ceased  their  activity  and  final  quiet  was  restored.  Probably 
an  upward  tendency  was  given  to  the  area,  but  it  must  have  been  very 
gradual  and  not  attended  by  the  distortion  which  so  frequently  accompanies 
mountain  l^uilding.  The  disintegrating  action  of  frost  and  rain  immediately 
set  in  aiid  has  carved  out  this  mountain,  in  the  heart  of  which  may  be 
read  the  story  of  its  origin. 

In  the  foothills  and  several  hundred  feet  above  the  valley  there  is  a  per- 
pendicular wall  of  breccia,  which  in  some  places  attains  a  height  of  nearly 
100  feet.  The  fossil  trunks  may  be  seen  in  this  wall  in  many  places,  all  of 
them  standing  upright  in  the  positions  in  which  they  grew.  Their  upright 
position  proves  that  if  there  have  been  changes  of  level  they  have  been 
gradual  and  in  the  same  plane,  as  otherwise  the  trunks  would  be  variously 
inclined.  Some  of  these  trunks,  which  are  from  2  to  4  feet  in  diameter 
and  20  to  40  feet  in  height,  are  so  far  weathered  out  of  the  rock  as  to 
appear  just  ready  to  fall,  while  others  are  only  slightly  exposed.  Niches 
mark  the  places  from  which  others  have  already  fallen,  and  the  foot  of  the 
cliff  is  piled  high  with  fragments  of  various  sizes. 

Above  this  cliff  the  fossil  trunks  appear  in  great  numbers  and  in  regular 
succession.  As  they  are  perfectly  silicified  the)'^  are  more  resistant  than  the 
surrounding  matrix,  and  consequently  stand  out  above  it.  In  most  cases 
they  are  only  a  few  inches  above  the  surface,  but  occasionally  one  rises  as 
high  as  5  or  6  feet. 

The  largest  trunk  observed  in  the  Park  is  found  in  this  locality.  It  is 
a  little  over  10  feet  in  diameter,  which  includes  a  portion  of  the  bark.  It 
is  very  much  broken  down,  especially  in  the  interior,  a  condition  which 
very  probably  prevailed  before  fossilization.  It  projects  about  6  feet  above 
the  surface. 

The  most  remarkable  of  all  the  forests,  however,  is  located  on  the  west- 
ern end  of  Specimen  Ridge,  about  1  mile  southeast  of  Junction  Butte  and 
opposite  the  mouth  of  Slough  Creek.  It  was  first  brought  to  the  notice,  of 
the  scientific  world  by  Mr.  E.  C.  Alderson  and  the  writer,  who  discovered 
it  in  August,  1887.  It  is  found  on  the  higher  portion  of  the  ridge,  and  is 
several  acres  in  extent.  The  trees  are  exposed  at  various  heights  on  a 
verjr  steep  hillside,  and  the  remarkable  feature  is  that  most  of  them  project 
well  above  the  surface. 


FOSSIL  FLOKA.  '  759 

One  of  the  largest  and  best-preserved  trees  stands  at  the  very  summit 
of  the  slope.  It  is  26  i  feet  in  circumfereuce  without  the  bark,  and  i-ises 
about  12  feet  in  heig-ht.  The  portion  of  this  huge  trunk  preserved  is  the 
base,  and  below  ground  it  becomes  somewhat  enlarged  and  passes  into 
the  roots,  which  are  as  large  as  the  trunks  of  ordinary  trees.  The  roots 
are  embedded  in  the  solid  rock,  as  shown  in  the  figure  (see  PI.  CIV). 

This  trunk  is  a  true  Sequoia,  and  is  so  closely  allied  to  the  modern 
redwood  (^Sequoia  sempervirens)  of  California  as  to  be  hardly  distinguishable 
from  it.  It  would  be  interesting  to  learn  the  height  this  tree  attained,  l)ut 
it  seems  safe  to  assume,  from  what  we  know  of  its  living  representative, 
that  it  must  have  been  -more  than  a  hundred  feet  high. 

Just  below  the  large  trunk,  on  the  steep  hillside,  are  two  more  stand- 
ing trees  (see  PI.  CVI),  which  we  may  imagine  to  have  formed  the  doorposts 
of  the  "ancient  temple"  of  which  Holmes  speaks.  They  stand  about  20 
feet  apart  and  rise  about  25  feet  in  height.  They  are  both  about  2  feet  in 
diameter  and  are  also  without  the  bark. 

In  other  parts  of  the  area  there  are  standing  trees  which  attain  a 
height  of  12  to  20  feet  They  are  all  under  2  feet  in  diameter.  In  a  few 
cases  the  bark  is  also  preserved.  It  is  hardly  ever  more  than  3  inches  in 
thickness. 

Scattered  about  over  the  area  are  a  great  many  trunks  that  rise  only  a 
few  inches  above  the  surface.  These  vary  in  diameter  from  2  to  5  feet. 
They  are  often  hollow  in  the  center  and  have  the  cavity  lined  with  brilliant 
amethyst  crystals. 

•  One  of  the  larger  trees  appears  to  have  been  prostrated  before  it  was 
fossilized  (see  PI.  CVIII).  It  is  about  4  feet  in  diameter  and  is  exposed  for 
a  length  of  40  feet.  There  is  nothing  to  indicate  the  portion  of  the  trunk 
in  its  relation  to  roots  and  branches,  but  neither  shows  on  the  exposed  part. 
There  is  no  appreciable  diminution  in  diameter,  and  consequently  it  must 
have  been  a  very  tall  trunk. 

The  matrix  about  the  bases  of  these  trees,  as  well  as  those  in  the  Fossil 
Forest,  contains  numerous  impressions  of  leaves,  branches,  and  fruits.  In 
the  Fossil  Forest  there  are  at  least  6  horizons  at  which  plant  remains  occur. 
These  are  separated  by  a  few  inches,  or  in  some  cases  by  many  feet.  In 
the  forest  last  described,  which  may  be  called  the  Junction  Butte  Forest, 
there  are  only  2  or  3  plant  horizons. 


760  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Most  of  the  trunks  in  all  three  of  the  described  forests  are  coniferous, 
but  occasionally  a  dicotyledonous  trunk  is  found,  showing  that  the  forest 
was  to  some  extent  a  mixed  one.  It  is  of  course  more  than  probable  that 
the  leaves  found  in  the  matrix  about  the  bases  of  the  trees  were  at  one 
time  attached  to  them,  but  as  the}^  have  never  been  found  in  association,  it 
is  manifestly  impossible  to  correlate  them. 

The  next  fossil  forest  in  rank  of  size  is,  perhaps,  the  one  found  on 
Cache  Creek,  about  7  miles  above  its  mouth.  It  is  exposed  on  the  south 
bank  oi  the  creek,  and  covers  several  acres.  The  trunks  are  scattered 
from  bottom  to  top  of  the  slopes,  through  a  height  of  probably  800  feet 
Most  of  the  trunks  are  upright,  although  there  is  only  now  and  then  one 
projecting  more  than  2  or  3  feet  above  the  surface.  The  largest  one 
observed  was  6  feet  in  height  and  about  4  feet  in  diameter.  While  most  of 
the  trunks  appear  to  the  naked  eye  to  be  coniferous,  there  are  a  number 
that  are  obviously  dicotyledonous.  It  is  certain,  however,  that  the  conifers 
were  the  predominant  element  in  this  as  in  the  other  fossil  forests. 

The  slopes  of  The  Thunderer,  the  mountain  so  prominently  in  view 
from  Soda  Butte  on  the  south,  have  also  numerous  fossil  trunks.  They  are 
mainly  upright,  but  onlj"  a  very  few  are  more  than  2  feet  above  the  surface. 
There  were  no  remarkably  large  trunks  observed,  the  average  diameter 
being  less  than  2  feet. 

Mount  Norris,  which  is  hardly  to  be  separated  from  The  Thunderer, 
has  a  fossil  forest  of  small  extent.  The  trees  are  of  about  the  same  size 
and  characteristics  as  those  on  the  larger  mountain. 

Forests  of  greater  or  less  extent,  composed  mainly  of  upright  trunks, 
are  exposed  on  Baronett  Peak,  Bison  Peak,  Abiathar  Peak,  Crescent  Hill, 
and  Miller  Creek.  In  fact,  there  is  hardly  a  square  mile  of  the  area  of  this 
northeastern  portion  of  the  Park  without  its  fossil  forest — scattered  trunks 
or  erratic  fragments. 

The  vast  area  to  the  east  of  the  Yellowstone  Lake  has  never  been 
explored  thoroughly  from  the  paleobotanical  side,  but  enough  is  known  to 
be  certain  of  the  presence  of  more  or  less  fossil  wood.  The  stream  beds 
contain  occasional  fragments,  which  is  a  sufficient  indication  that  trunks 
of  trees  must  be  near  at  hand. 


FOSSIL  FLOUA.  761 

DESCRIPTION  OF  8PKC1ES. 

Sequoia  iMAgnifica  n.  sp. 
Pis.  CIV,  OV,  CX,  GXI,  CXVII,  figs.  1-6. 

Diagnosis. — Truuks  ot'tc'U  of  great  size,  6  to  10  feet  in  diameter,  30  feet 
high  as  now  preserved,  bark  when  present  5  or  6  inches  in  thickness; 
annual  rings  very  distinct,  2  to  3  nun,  broad;  fall  wood  reduced  to  narrow 
bands  of  3  to  If)  rows  of  thick-walled  cells;  cells  of  spring  and  summer 
wood  large,  hexagonal  or  often  elongated;  resin  tubes  numerous,  composed 
of  short  cells;  medullary  rays  numerous,  of  a  single  series  or  occasionally 
with  a  partial  double  series  of  superimposed  cells;  wood  cells  with  one  or 
two  rows  of  small  circular  pits. 

Transverse  section. — In  tliis  scctiou  (Pls.  CX,  CXI)  the  structure  appears 
beautifully  preserved.  The  rings  are  rather  narrow,  being  only  2  or  3  mm. 
broad,  or  often  only  1  mm.  They  are  verj'  sharply  deraarked,  even  to  the 
naked  eye.  Under  the  microscope  the  rings  are  found  to  consist  of  a  band 
of  thick- walled  cells  that  is  never  more  than  15  rows  of  cells  deep  and 
often  is  reduced  to  2  or  3  rows.  The  cells  composing  the  spring  and  summer 
wood  are  of  uniform  size  and  inclined  to  be  hexagonal  in  shape.  Those  of 
the  fall  wood  are,  of  course,  compressed. 

The  resin  cells  are  numerous  and  may  be  readily  distinguished  by 
the  dark  contents.     They  occiu*  mainly  in  the  spring  and  summer  wood. 

The  medullary  rays  seen  in  this  section  are  long,  straight,  and  sepa- 
rated by  usually  about  3  rows  of  wood  cells. 

Radial  section. — Tliis  scctiou  (PI.  CXVI,  figs.  2-3)  Is  the  least  satisfactory 
of  all.  The  wood  cells  show  well  under  the  microscope,  but  their  mai'kings 
are  very  obscure.  By  prolonged  search  it  is  made  out  that  the  pits  are  in 
1  row,  or  sometimes  2  parallel  rows.  They  are  small,  as  far  as  can  be  made 
out,  and  are  too  obscure  for  satisfactory  measurement. 

The  rays  are  composed  of  long,  unmarked  cells. 

Tangential  section. — This  scctiou  (Scc  PI.  CXYI,  fig.  1)  is  Very  satisfactory. 
The  wood  cells  are  long  and  unmarked.  The  resin  ducts  are  numerous, 
but  scattered,  the  cells  being  twice  or  three  times  as  long  as  wide.  In 
many  cases  they  are  filled  with  or  contain  masses  of  dark  material,  repre- 
senting the  resin  now  turned  to  a  carbonaceous  mass. 


762  GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

The  meduUaiy  rays  are  composed  of  1,  or  in  some  cases  of  a  par- 
tially double,  series  of  2  to  about  25  superimposed  cells.  They  are  large 
and  quite  thick  walled.  The  average  number  of  cells  iu  each  ray  is 
about  12. 

This  species  is  closely  related  to  the  living  Sequoia  sempervirens  Endl., 
more  closely  than  any  other  fossil  species  with  which  I  am  familiar.  They 
are  hardly  to  be  separated  by  any  well-defined  characters.  The  living- 
wood  has  the  same  clearly  marked  annual  rings^  resin  cells,  partially  double 
rays,  and  pits  on  the  wood  cells.  The  medullary  rays  in  the  living  wood 
are  provided  with  numerous  round  pores  or  markings.  These  seem  to  be 
absent  from  the  fossil  specimens,  but,  as  already  related  under  the  diagnosis, 
the  fossil  is  not  well  preserved  in  the  radial  section  and  they  may  have 
been  present  there  when  it  was  living.  The  dimensions  of  the  various 
elements  are  much  the  same  in  the  living'  and  fossil  specimens,  thus  leaving 
no  doubt  as  to  their  close  affinity. 

In  size  of  trunks  these  species  are  also  similar.  The  largest  trunks 
observed  in  the  Yellowstone  National  Park  belong  to  S.  magnlfica.  They 
range  in  size  from  4  to  10  feet  in  diameter,  one  of  the  largest  being  shown 
on  PI.  CV.  This  is  26J  feet  in  circumference  and  stands  upright  on  the 
hillside.  It  is  12  feet  high,  and  I'epresents  the  base  of  the  trunk,  as  the 
large  roots  are  well  preserved.  Their  height  is  of  course  unknown,  but  one 
was  fortunately  prostrated  before  fossilization  (PI.  CVIII),  and  is  40  feet 
long,  with  no  apparent  diminution  in  diameter.  It  is  altogether  likely  that 
they  may  have  been  equal  in  height  to  some  of  the  living  representatives. 

I  have  thought  best  to  give  this  fossil  species  a  name  different  from 
that  of  the  living  tree,  notwithstanding  the  fact  that  they  are  evidently  so 
closely  related.  The  fossil  comes  from  a  locality  remote  geographically 
from  the  living  redwood,  and,  moreover,  from  a  horizon  that,  although  com- 
paratively recent,  is  so  ancient  as  to  make  it  extremely  improbable  that 
the  type  has  actually  been  living  for  so  long  a  period.  There  can,  however, 
he  no  doubt  that  the  living  redwood  is  the  direct  descendant  of  this 
remarkable  tree  that  was  once  so  abundant  in  the  Yellowstone  National 
Park. 

Habitat:  Specimen  Ridge,  Fossil  Forest  at  head  of  Crystal  Creek, 
Fossil  Forest  on  Cache  Creek,  etc.;  collected  by  F.  H.  Knowlton,  August, 
1887-August,  1888. 


FOSSIL  FLORA.  763 

PiTYOXYLON   ALDERSONI    U.    sp. 
Pis.  CVr,  CXII,  CXIII,  CXVIII,  tigs.  S,  i;  PI.  OXIX,  fig.  2. 

Diagnosis. — Tvuiiks  of  Ijirye  size,  3  to  5  feet  in  diameter;  annual  rings 
very  distinct,  often  8  or  9  mm.  broad,  very  sharply  demarked;  resin  ducts 
numerous,  large,  scattered,  occurring  in  late  summer  and  fall  wood;  wood 
cells  long,  with  a  single  irregular  row  of  medium-sized  pits;  medullary  rays 
in  a  single  series,  or  occasionally  with  divided  cells;  rays  from  2  to  25 
cells  high,  the  average  being  about  10  or  12  cells. 

Transverse  section. — The  anuual  Hugs  are  very  distinct,  being  plainly  dis- 
cernible to  the  naked  eye.  Some  of  the  broadest  rings  are  fully  9  mm. 
wide,  and  none  are  less  than  6  mm.  The  demarcation  between  fall  and 
spring  wood  is  very  pronounced  (see  fig.  4  of  PI.  CXVIII  and  2  of  PI. 
CXIX),  the  cells  of  fall  being  small,  compressed,  and  thick-walled,  while 
those  of  the  early  spring  v\'ood  are  very  large,  and,  of  course,  thin-walled. 

The  cells  of  the  spring  and  summer  wood  continue  for  a  width  of 
5  mm.,  but  little,  if  any,  diminished  in  size.  Then  they  become  slightly 
smaller  and  thicker-walled  and  pass  gradually  into  the  fall  wood. 

The  resin  ducts  ai'e  very  large.  They  are  not  found  in  the  summer 
wood,  but  occur  irregularly  in  the  early  fall  and  late  fall  wood. 

The  medullary  I'ays,  as  observed  in  this  section,  are  straight  and 
separated  by  from  3  to  8  or  10  rows  of  wood  cells.  The  individual  cells 
are  apparently  long. 

Radial  section. — Notwitlistaudiug  the  fact  that  the  wood  seems  to  be  per- 
fectly preserved,  it  does  not  reveal  the  structure  well  in  this  section.  The 
wood  cells  are  seen  to  be  sharp-pointed  where  they  join.  They  are,  of 
course,  broad  in  the  spring  and  summer  wood,  and  very  narrow  and  thick- 
walled  in  the  fall  wood.  It  is  very  difficult  to  make  out  the  pits,  but  in 
exceptionally  well  preserved  portions  a  few  may  be  faintly  seen.  They 
are  scattered,  but  in  a  single  series.  They  are  so  obscure  that  no  satis- 
factory measurements  can  be  made. 

The  medullary  rays  in  this  section  are  long,  thick-walled,  and  without 
markiiigs,  so  far  as  can  be  made  out. 

Tangential  section. — Tlils  sectiou  is  Very  plain.  The  medullary  rays  are 
numerous  and  in  a  single  series,  although  occasionally  a  ray  may  be  observed 
in  which  there  are  2  series  of  cells  for  a  short  distance.     In  such  cases  the 


764  GEOLOGY  OF  THE  YELLOWSTONE  jSTATIONAL  PARK. 

cells  are  always  smaller  than  the  ordinary  ray  cells.  The  number  of 
cells  making  up  each  ray  ranges  from  2  to  30  or  more,  but  the  average 
number  is  about  8  to  15. 

The  rays  in  which  there  is  a  resin  duct  are  rather  rare.  The  duct  is 
large,  taking  up  all  the  width  of  the  ray.  The  remainder  of  the  ray  is  3 
rows  of  cells  high  in  the  middle  and  is  reduced  to  1  at  the  extremities. 

The  wood  cells  show  clearly  in  this  section.  They  are  not  provided 
with  pits  or  other  markings. 

Habitat:  Specimen  Ridge,  Fossil  Forest,  near  head  of  Crystal  Creek; 
collected  by  F.  H.  Knowlton,  August,  1887.  Yancey  Fossil  Forest;  col- 
lected by  F.  H.  Knowlton,  August,  1887. 

PiTYOXYLON    AMETHYSTINUM   11.  Sp.^ 
Pis.  GVII,  GVIII,  OXIV,  CXV,  CXVIII,  figs.  1,  2. 

Diagnosis. — Truiiks  of  siuall  or  medium  size ;  annual  rings  sharply 
demarked,  3  to  8  mm.  broad;  resin  ducts  numerous,  scattered,  but  mainly 
ill  fall  wood;  wood  cells  long,  sharp-pointed,  provided  with  a  single  row  of 
scattered,  small,  somewhat  irregular  pits;  medullary  rays  numerous,  in  a 
single  series  of  '2  to  12  cells,  the  average  being  about  5  or  6. 

Transverse  section. — Mucli  likc  tlic  precodiiig  spccles,  exccpt  that  the  rings 
are  narrower,  the  cells  of  spring  and  summer  wood  are  smaller,  and  the 
late  fall  cells  have  thinner  walls.  The  resin  ducts  are  also  much  the  same, 
being  in  general  only  a  little  smaller.  A  few  are  found  in  the  summer 
wood,  but  most  of  them  are  in  the  fall  wood.  The  rays  are  not  nearly  so 
numerous  as  in  the  last  species.  They  are  often  separated  by  as  many  as 
25  rows  of  wood  cells. 

Radial  section. — TliB  radial  section  of  nearly  all  woods  from  the  Yellow- 
stone National  Park  is  more  or  less  obscure.  The  one  under  consideration 
is  no  exception  to  this  rule,  and  it  is  only  after  considerable  search  that  the 
pits  can  be  determined.     They  are  hi  a  single  row  (see  PI.  CXVIII,  fig.  1) 

'  In  1888  Dr.  .1.  Felix,  of  Berlin,  visited,  and  collected  fossil  wood  in,  the  Yellowstone  National 
Park.  The  results  of  his  work  were  published  in  Zeitschrift  der  Ueutschen  geologischen  Gesellschaft, 
for  1896.  He  described  six  species  of  fossil  wood,  of  wliieh  number  I  have  recognized  four.  The 
following  two  species  were  not  tignred,  and  as  the  locality  whence  they  came  is  more  or  less  in  doubt 
I  have  not  included  them  in  the  systematic  enumeration.  They  are  as  follows :  Piti/oxylon  faUax  and 
Cupressinoxyton  eulreton.  They  may  be  identical  with  certain  of  the  species  I  have  described,  bnt  of 
this  I  am  uncertain. 


FOSSIL  FLORA.  7G5 

ami  lire  rather  small.  They  are  so  obscure  that  it  is  impossible  to  make 
trustworthy  uieasurements. 

The  uiedullary  rays,  as  seen  in  this  section,  are  composed  of  long-,  thin- 
walled  cells,  and  so  fur  as  can  be  determined  the}'  are  without  pits  or  other 
markinys. 

Tangential  section. — This  soctiou  (I'l.  CXVIII,  fig.  2)  sliows  the  structuro 
very  plainl}".  The  medullary  rays  are  abundant  and  always  in  a  single 
series,  except  the  large  compound  ones.  The  number  of  cells  in  each  ray 
varies  fi'om  2  to  10  or  12,  the  average  number  being  about  6.  The  com- 
pound rays  inclosing  the  resin  ducts  are  rather  small,  with  three  rows  of 
cells  in  the  middle  portion.  No  markings  can  be  made  out  on  the  wood 
cells  in  this  section. 

This  species  is  very  closely  allied  to  the  one  preceding,  and  should 
perhaps  be  referred  to  it.  The  main  points  of  difference  are  the  following: 
Narrower  annual  rings;  smaller  resin  ducts,  that  are  occasionally  found  in 
tlie  summer  wood;  smaller  wood  cells  throughout;  smaller  and  shorter 
compound  medullary  rays;  ordinary  rays  always  in  a  single  series  of  2  to 
12  cells  (average  6)  instead  of  from  2  to  30  or  more  (average  12). 

Habitat:  Specimen  Ridge,  Fossil  Forrest,  near  head  of  Crystal  Creek; 
collected  by  F.  H.  Knowlton,  August,  1887. 

Laurinoxylox  pulchrum  n.  sp. 
Pis.  CXVI,  CXIX,  figs.  3-5;  PI.  CXX,  fig.  1. 

Transverse  section. — Auuual  Hug  vcry  distluct  to  the  naked  eye,  2  to  4  mm. 
broad.  The  demarcation  between  the  rings  results  from  10  or  12  layers 
of  thicker- walled  cells,  representing  the  late  fall  wood,  and  from  the  greater 
abundance  of  ducts  in  the  immediately  following  spring  wood. 

The  wood  cells  are  small  and  arranged  in  serial  rows  except  in  the 
vicinity  of  the  ducts,  where  they  are  somewhat  irregular  (see  fig.  1  of  PI. 
CXX).  Surrounding  the  ducts,  and  sometimes  filling  the  remainder  of  the 
space  between  rays,  the  cells  are  larger  and  not  so  completely  seriated. 
The  ordinary  wood  cells  are  about  0.01  mm.  in  diameter,  and  those  near  the 
ducts  0.015  or  0.02  mm.  There  is  an  occasional  row  of  the  larg-e-sized 
wood  cells  along  a  ray,  as  in  fig.  1  of  PI.  CXX. 

The  ducts  are  very  plainly  shown  in  this  section.  At  least  half  of 
them  are  single  and  nearly  or  quite  circular  in  section.     Of  the  remainder, 


766  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PAHK. 

most  are  double,  while  occasionally  there  are  3  iu  a  row  or  series,  and 
exceptionally  as  many  as  4.  The  number  in  a  square  millimeter  is  only 
from  4  to  6.  The  smallest  of  the  single  ducts  range  in  diameter  from 
0.03  to  0.06  mm.  The  largest  observed  are  0.21  mm.  in  long  diameter 
and  0.16  mm.  iu  short  diameter.  The  largest  double  duct — that  is,  when 
there  are  two  tog-ether — is  0.31  mm.  The  largest  of  the  series  of  3  is  0.36 
mm.,  and  the  largest  of  the  few  in  series  of  4  is  0.44  mm.  The  average 
diameter  of  large  and  small  ducts  is  probably  about  0.12  mm. 

The  medullary  rays  are  1  to  3  cells  wide,  and  run  irregularly  among 
the  ducts.     They  are  about  0.01  nun.  broad. 

Radial  section. — The  wood  cells  are  long,  slender,  and  apparently  sharp- 
pointed.  There  is  evidence  also  that  some  of  these  are  divided  up  into 
short  cells  by  square  divisions. 

The  medullary  rays  forn:i  plates  of  short,  rather  thin-walled  cells. 
They  are  from  0.02  to  0.04  mm.  in  diameter  and  from  0.05  to  0  09  mm.  in 
length.  They  do  not  appear  to  be  marked,  yet  there  is  some  evidence  that 
there  were  minute  j)its;  but  the  specimens  are  not  well  enough  preserved 
to  be  cei'tain  of  this. 

The  ducts  shown  in  longitudinal  section  (PI.  CXIX,  fig.  3)  are  very 
pronounced.  The  individual  cells  are  from  0  10  to  0.20  mm.,  or  some- 
times more,  in  length.  The  walls  ere  covered  with  small  round  pits,  which 
occasionally  pass  into  regular  scalariform  markings  (see  figs.  4  and  5  of 
PI.  CXIX.)  Each  duct  is  surrounded  by  a  mass  of  tissue  from  2  to  6  or  8 
layers  of  cells  thick,  of  which  mention  was  made  under  the  discussion  of 
the  transverse  section.  The  individual  cells  of  this  sheath  are  of  about  the 
same  size  and  appearance  as  the  large  cells  of  the  medullary  rays. 

Tangential  section. — The  fiuc  pliotomicrograpliic  reproductions  of  this  section 
(PI.  CXVI)  give  a  far  better  idea  of  the  structure  than  any  desci'iption  can. 
The  medullary  rays,  it  will  be  observed,  are  very  numerous  (about  3  to 
each  square  millimeter).  They  are  from  1  to,  exceptionally,  4  layers  of 
cells  broad  and  about  12  layers  high,  the  extremes  being  5  and  20. 

This  plate  shows  admirably  the  ducts  and  related  tissue.  The  one  in 
the  center  of  the  plate  shows  well  the  manner  of  division,  although  the 
magnification  is  hardly  sufficient  to  show  the  pits  or  markings. 

This  species  is  one  of  the  handsomest  with  which  I  am  familiar.  It 
has  affinities  with  a  number  of  described  forms,  as,  for  example,  Laurus 


FOSSIL  FLOHA.  767 

triseriata  Caspary,'  from  the  Tertiary  of  Prussia.  From  this  it  differs 
in  the  arrangement  of  (luets  and  in  rays,  and  somewhat  in  the  markings. 
It  is  also  evidently  allied  to  the  two  forms  from  the  Tertiary  of  Arkansas, 
Laurinoxi/loii  hnmnen  Kn.^  and  L.  h'Sfjiwreiwiaiia  Kn.^ 

The  genus  Laurus  was  evidently  abundant  in  this  flora,  and  it  is  to  be 
expected  that  the  trunks  would  be  occasionally  preserved.  It  is  of  course 
probable  that  this  wood  may  belong  to  a  species  that  has  also  been  described 
from  the  leaves,  but  there  is  manifestly  no  means  of  connecting  them. 

Habitat:  Specimen  Ridge  Forest,  near  head  of  Crystal  Creek,  Yellow- 
stone National  Park,  a  prostrate  log;  collected  by  F.  H.  Knowlton.  August 
25,  1887. 

Perseoxylon  akomaticum  Felix. 

Perseo,rylon  aromaticum  Felix:  Untersucbiiag  liber  fossile  Holzer,  v.  Stiick:  Zeitsclir. 

d.  Deutscli.  geol.  Gesell.,  Jahr.  1806,  p.  254,  1S!)(J. 
Laurinoxylon  aromaticum  Felix :  Die  Holzopole  Unganis,  p.  27,  PI.  I,  tig.  7 ;  II,  fig.  7, 9. 

This  species  was  detected  by  Felix  in  his  visit  to  tlie  Yellowstone 
National  Park  in  1888.     I  did  not  meet  with  it. 

Habitat:  Vicinity  of  Yanceys,  Yelhiwstone  National  Park.  Collected 
by  J.  Felix,  1888. 

Plataninium  haydeni  Felix. 

PI.  OXX,  flgs.  3-5. 

Plataninium  haydeni  Felix:  Uutersuchung  ilber  fossile  Holzer,  v.  Stiick:  Zeitsclir.  d. 
Deutsch.  geol.  Gesell.  Jabr.  1890,  p.  251,  1890. 

Transv;rse  section. — The  aunual  Hugs  are  faint,  yet  they  niay  be  seen  with 
the  naked  eye.  I'hey  are  about  2  mm.  broad.  The  medullary  rays  are 
very  distinct  in  the  weathered  specimen. 

Under  the  microscope  the  structure  is  shown  to  be  well  preserved. 
The  wood  cells  ai'e  not  arranged 'in  radial  rows,  but  are  quite  irregularly 
placed.  They  are  large  (0.01  to  0.03  mm.)  and  angular,  being  3  to  6  sided 
by  compression. 

'  Einige  fuss.  HiJlzer  Pronssens:  Abhaudl.  z.  geol  Specialk.  v.  Prens.sen  u.  Thiiriugischen 
Staateu,  1889,  p.  60,  PI.  XI,  figs.  6-lL';  PI.  XII,  tigs.  1-5. 

=  Fossil' woods  and  lignites  of  Arkausas:  Aim.  Kept.  Geol.  Survey  Arkansas,  1889,  Vol.  II,  p.  256, 
PI.  IX,  figs.  8-9;  PI.  X,  figs.  1,2;  PL  X,  fig.  4. 

30p.  cit.,  p.  258,  PI.  X,  flgs.  3,4;  PI.  XI,  flgs.  3,4. 


768  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

The  ducts  (PI.  CXX,  fig.  4)  are  veiy  numerous.  They  occupy  at 
least  one-third  of  the  area,  exclusive  of  the  rays.  They  are  almost  always 
single,  although  often  placed  clo.se  together,  especially  in  the  beginning  of 
the  spi'ing  wood.  They  are  uniformly  oblong  in  shape.  In  the  spring 
wood  the  average  size  is  0.09  mm.  in  long  and  0.06  mm.  in  short  diameter. 
In  tlie  fall  wood  they  are  from  0.03  to  0.06  mm.  in  long  and  0.025  to  0.05 
mm.  in  short  diameter. 

The  annual  ring  consists  of  a  layer  of  slightly  thicker  Avood  cells,  but 
it  is  mainly  distinguished  by  the  abruptly  larger  ducts  in  the  spring  wood 
(see  fig.  4  of  PI.  CXX). 

The  medullary  vays  are  very  abundant  as  seen  in  this  section.  They 
are  from  1  to  10  or  15  cells  broad.  Fully  30  per  cent  of  the  ai-ea  is 
covered  by  the  medullary  rays.  The  ra3^s  uniforndy  contain  a  black  car- 
bonaceous substance,  these  making  them  stand  out  in  bold  relief 

Radial  section. — Tlic  uiost  promiuent  feature  in  this  section  (PI.  CXX,  fig. 
5)  is  the  medullary  rays.  They  form  high  plates  of  usually  short  cells 
with  black  carbonaceous  contents.  The  ducts  are  also  prominent,  and 
appear  to  be  marked  with  scalai'iform  thickenings;  but  as  they  are  quite 
obscure,  this  is  not  positive. 

Tangential  section. — Tho  structure  of  this  sectiou  is  very  clearly  revealed 
under  the  microscope.  The  medullary  rays  are  very  numerous.  They 
range  from  1  to  10  or  15  laj^ers  of  cells  broad  and  more  than  100  high. 
The  cells  are  round,  thin-walled,  and  usually  or  not  at  all  compressed. 
They  take  up,  as  already  stated,  fully  30  per  cent  of  the  space.  In  some 
cases  the  rays  are  0.5  mm.  long  and  0.35  ram.  broad  (cf.  fig.  3  of  PI.  CXX). 

The  wood  cells  are  long  and  sharp-pointed.  So  far  as  can  be  made 
out,  there  are  few  if  any  square  divisions  of  the  cells. 

The  ducts,  of  course,  show  well  in  this  section,  but  the  markings,  if 
present,  are  now  obscure. 

This  species  is  quite  closely  related  to  the  living  Platanus  occidentalis 
L.,  the  common  sycamore  or  plane  tree.  The  living  wood  shows  the  indis- 
tinct annual  ring,  the  in-egular  wood  cells,  and  numerous  medullary  rays 
almost  identical  with  the  fossil  wood.  There  are  certain  minor  points  of 
diff'erence,  such  as  markings  on  the  rays,  lignification  of  the  ducts,  etc.,  but 
they  are  certainly  close  enough  to  make  their  generic  identity  reasonably 
•sure. 


FOSSIL  FLORA.  739 

The  fact  that  IMatamis  leaves  are  very  al)umhnit  in  the  beds  surroimd- 
ino-  the  fossil  trunks  makes  it  extremely  i)rol)al)le  that  the  generic  reference 
is  correct.  It  is  of  course  also  ])rol)able  that  some  of  the  leaves  belong  to 
the  wood  here  described  as  different,  but  as  they  have  never  been  fmuid 
attached,  it  is  manifestly  unsafe  to  assume  that  there  was  ever  organic 
union. 

A  number  of  fossil  species  have  been  described  from  various  2:>arts  of 
the  world;  none,  however,  from  North  America.  The  general  agreement 
between  these  and  the  one  under  consideration  is  close,  but  the  siDecific 
differences  are  marked  in  certain  cases.  One  of  the  nearest  forms  is 
PManus  klehsii  Gasp.,'  from  the  Tertiary  of  Prussia.  It  differs  in  important 
minor  characters,  as  does  P.  borealis  Casp.,^  from  the  same  place.  The  two 
species  described  by  Felix,  Plafamnunn  porosim  Felix  and  P.  regulare 
Felix,  have  only  general  resemblance. 

In  the  original  MS.,  which  was  submitted  in  March,  1896,  I  had  of 
course  given  this  another  specific  name,  and  it  may  still  prove  to  be  different 
froni  the  P.  liaijclem  of  Felix.  Unfortunately  Felix  has  not  figured  his 
species,  and  it  is  difficult,  from  a  mere  technical  description,  to  be  entirely 
certahi  of  their  identity.  It  is  reasonably  certain,  however,  that  they  are 
identical,  and  I  have  so  regarded  them. 

Habitat:  Specimen  Ridge  Forest,  near  head  of  Crystal  Creek,  Yellow- 
stone National  Park.  From  a  trunk  6  inches  in  diameter  and  about  1  foot 
in  height;   collected  by  F.  H.  Knowlton,  August  25,  1887. 

Rhamnacinium  radiatum  Felix. 

PI.  CXVIII,  flgs.  6,  7;  P].  CXIX,  fig.  1. 

RhamnacinmmradiatmnYeli^-.  UntersuchuugiiberfossileHoIzer:  Zeitscbr  d  Deutsch 
geol.  (iesell.,  Jahr.  1896,  p.  252,  PI.  VI,  fig.  3,  1896. 

Tran.ver=esectic„._Annual  ring  broad  (7  mm.),  very  indistinct,  consisting 
ol  only  1  or  2  rows  of  slightly  thickened  wood  cells  and  rather  abrupt 
presence  of  numerous  large  ducts  in  succeeding  spring  wood.  Ducts  very 
numerous,  in  radial  rows.  A  few  of  the  ducts  are  single,  hxu  mainly  they 
are    contiguous,  with  ^Jo^(Mn^a  series.     The  usual  number  is   3  or 

=  0p.  cit.,Pl.  IX,  figs.  1-11. 
MON  XXXII,  PT  II 49 


770  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

four.  The  ducts  occupy  uearly  oue-half  of  the  area,  thu&  producing  an 
open,  soft  wood.  The  longest  series  of  ducts,  embracing  10,  is  0.50  nun. 
in  length.  Series  of  4  or  5  having  a  length  of  0.30  nun.  are  common. 
The  small  single  ducts  are  0.05  to  0.07  mm.  in  long  and  0.04  to  0.05  mm. 
in  short  diameter.  The  average  short  diameter  of  all  ducts  is  about  0.07 
or  0.08  mm. 

The  wood  cells  are  arranged  in  distinct  radial  rows.  They  are  rather 
large  and  thin-walled,  also  showing  that  the  wood  was  a  soft,  porous  one. 

The  medullary  rays  in  this  section  are  rather  numerous.  They  are 
2  or  sometimes  3  cells  wide,  and  the  cells  are  short  and  thin-walled. 

Radial  section. — The  ducts  appear  especially  numerous  in  this  section. 
The  marking  on  the  walls  is  rather  obscure,  but  they  seem  to  be  uniformly 
provided  with  minute  pits. 

The  rays  form  high  plates  of  short,  thin-walled  cells,  apparently  with 
small  circular  or  oblong  pitlike  markings. 

The  wood  cells  are  very  long.  They  have  sharji-pointed  extremities 
and  thin  walls. 

Tangential  section. — Tliis  sectiou  Is  xevj  cliaracteristic,  the  most  prominent 
feature  being,  of  course,  the  cut-off  ends  of  the  medullary  rays.  The  rays 
are  ^'arious,  being  2  or  rarely  3  or  4  layers  of  cells  wide.  The  number  of 
vertical  rows  is  very  indefinite,  being  rarely  less  than  10  or  more  than  30. 
The  cells  are  rectangular,  being  often  twice  as  long  as  wide.  Some  of  the 
cells  in  the  middle  of  the  ray  are  more  or  less  irregular  in  shape.  All  are 
very  thin-walled. 

The  wood  cells  are  the  same  as  in  the  radial  section. 

The  ducts  are  also  prominent.  The}-  liave  oblique  partitions  and  the 
walls  are  provided  with  round  pits.  The  markings  on  the  walls  are  not 
different  from  those  to  be  observed  in  the  radial  sectiou,  but  they  happen  to 
l)e  better  preserved. 

In  my  original  MS.  this  form  was  described  under  the  new  generic 
name  of  Populoxylon,  from  its  undoubted  close  resemblance  to  wood  of 
living  Populus.  It  is  with  some  hesitation  that  I  transfer  it  to  Felix's 
species,  for  they  do  not  agree  in  every  particular.  On  the  whole,  however, 
it  is  more  than  probable  that  they  are  the  same,  and  I  have  so  regarded 
them      The  generic  diagnosis,  based  uptm  the  wood  from  the  Park  only. 


FOSSIL  FLOKA.  771 

may  be  drawn  up  as  follows:  Annual  rin<4-  present,  ])ut  faintly  deniarked; 
wood  cells  long-,  narrow,  sharp-pointed,  thin-walled;  ducts  very  numerous, 
occu})vinf>"  about  one-half  of  the  area,  in  radial  rows  of  from  2  to  10, 
pitted,  the  pits  small,  round;  medullary  rays  numerous,  of  short,  thin-walled 
cells,  rectangular  or  irregular  in  transverse  section,  arranged  in  2  to  some- 
times 4  vertical  rows  of  approximately  10  to  30  cells  each. 

Habitat:  Specimen  Ridge,  near  head  of  Cr3-stal  Creek,  Yellowstone 
National  Park;  collected  by  F.  H.  Knowlton,  August  22,  1,S87. 

QUERCINIUM    LAMARENSE  n.  Sp. 
PI.  CXVni,  fig.  5;  PL  OXX,  fig-.  2;  PI.  CXXI,  figs.  1,  2. 

Transverse  section. — Auuual  riug  preseiit,  but  vcry  falut ;  consisting  of  but 
1  or  2  rows  of  thickened  cells.  In  the  succeeding-  spring  wood  the  ducts 
are  much  larger,  thus  making  the  ring  visible  to  the  naked  eye. 

Ducts  numerous,  scattered,  most  abundant  in  spring  and  summer 
wood;  all  single — that  is,  not  contiguous.  They  are  almost  perfectly 
circular,  being  very  slightly  elongated  radially.  They  are  large,  though 
not  remarkably  so  for  the  genus;  the  larger  ones  ranging  in  diameter 
from  0.16  to  0.23  mm.,  the  smaller  being  about  0.20  mm.  The  very 
smallest  ducts  are  0.05  mm.  in  diameter,  and  the  more  common  of  the 
small  ones  are  0.10  or  0.12  mm.  in  diameter.  None  of  the  ducts  are 
arranged  in  notable  radial  rows. 

The  wood  cells  are  in  distinct  radial  rows,  and  are  large  and  thick- 
walled.  In  most  the  lumen  is  nearly  obliterated.  The  average  size  of  the 
wood  cells  is  0.02  mm. 

The  medullary  rays  are  neither  very  numerous  nor  conspicuous.  They 
are  mainly  only  1  cell  broad,  with  au  occasional  wide  one  of  20  or  more 
cells,  as  will  be  described  under  the  tangential  section.  Some  of  the  single- 
celled  rays  pass  for  a  considerable  distance  among  the  ducts,  but  by  far  the 
larger  number  lie  between  two  ducts  (see  fig.  1  of  PI.  CXXI). 

Radial  section. — The  ouly  scctious  available  in  this  direction  were,  unfor- 
tunately, from  poorly  preserved  portions  of  the  specimen,  and  do  not  show 
the  structure  clearly.  The  wood  cells,  so  far  as  can  be  made  out,  are  ver}* 
long,  and,  as  shown  by  the  transverse  section,  have  thick  walls      The  rays 


772  GEOLOGY  OF  THE  YELLOWSTONE  :N^ATI0NAL  PAEK. 

form  high  phites  of  cells,  the  exact  length  of  which  can  not  be  determined 
with  satisfaction.  If  there  were  markings  on  the  rays  they  can  not  be  seen; 
neither  can  the  markings  on  the  ducts  be  observed. 

Tangential  section. — Tlus  scctlon  sliows  much  better  under  the  microscope 
than  the  radial  one. 

The  rays  are  found  to  be  of  two  distinct  kinds:  The  most  numerous 
are  only  1  cell  broad  and  from  10  to  25  cells  high,  the  individual  cells 
being  thin-walled  and  oblong  in  shape.  At  scattered  intervals  are  veiy 
broad  rays  composed  of  10  to  20  rows  of  cells  and  extending  for  long 
distances  through  the  section  (see  fig.  2  of  PI.  CXXI).  These  broad  rays 
are  often  somewhat  cut  by  wood  cells  passing  diagonally  through  them 
(see  fig.  2  of  PI.  CXXI).  This  does  not,  however,  interfere  with  the  ray 
as  a  whole,  which  is  clearly  demarked  from  the  small  rays  of  a  single 
series  of  superimposed  cells.  The  individual  cells  of  the  large  rays  are 
nearly  circular  in  cross  section,  or  more  or  less  6-sided  by  mutual  pressure. 
They  are  also  thin-walled. 

Associated  with  the  small  rays  is  usually  a  layer  or  two  of  short-celled 
tissue  or  series  of  parenchymatous  cells.  Except  for  there  being  shorter 
cells  they  are  not  to  be  distinguished  from  the  ordinary  wood  cells. 

The  ducts  show  clearly  enoiigh  in  this  section,  but  they  are  not  well 
enough  preserved  to  permit  the  markings  on  the  walls  to  be  made  out.  It 
would  seem  that  the  walls  were  pitted,  but  this  is  largely  surmised. 

A  considerable  luimber  of  species  of  Quercinium,^  or  oak  wood,  in  a 
fossil  state,  have  been  described  from  various  parts  of  the  world.  Wood 
of  this  kind  is  readily  distinguished  by  the  large  isolated  ducts  and  the  two 
kinds  of  medullary  rays. 

The  species  under  consideration  resembles  a  number  of  described 
forms,  but  they  are  all  from  the  Old  World,  and  are  readily  distinguished 
from  it. 

This  species  is  closely  allied  to  Quercinium  hnowltoni  Felix,  and  may 
possibly  be  the  same,  but  as  Felix's  species  is  not  fully  illustrated  it  is 
difficult  to  be  positive.  Q.  lamarensc  seems  to  differ  in  the  shape  and  size 
of  the  large  ducts,  but  it  will  need  a  careful  comparison  of  the  sections  to 
be  positive.     For  the  present,  at  least,  they  may  remain  distinct. 

Habitat:  Specimen  Ridge,  Yellowstone  National  Park;  specimen  from 


'  Fifteen  species  and  varieties. 


FOSSIL  FLORA. 


i  iO 


an  uprifi'lit  trunk,  4  feet  in  diiunoter;   colloctt'd  hy  F.  H.  Knowlton,  Auj^ust 
22,  1887 

QrERCINIUJI    KNOWLTONI    FcHx. 

Qtiereinium  hnoirltoni  Felix:   IJndersuchiuig  iiberfossile  Hillzer:  Zeitsclir.  d.  Doutsdi. 
gftol.  (icsell.,  Jahr.  IS'.H!,  ii.  250,  PI.  VI,  tig.  li,  ISDU. 

As  .stated  under  tlie  jtreceding  species,  these  2  forms  may  be  identi- 
cal, but  in  absence  of"  full  drawings  of  Q.  hioivltonl  it  seems  best  to  regard 
them  as  distinct.     The  size  and  sha])e  of  the  ducts  certainh'  dift'er  greatlv. 

Habitat:  Amethyst  Mountain,  Yellowstone  National  Park;  collected 
by  J.  Felix  in  1888. 

BIOLOGICAL   OOIVSIDERATIOX   OF   THE  TEKTIARY  FLORA. 

The  Tertiary  flora  of  the  Yellowstone  National  Park  possesses  great 
biological  interest.  It  is  a  rich  flora,  and  on  comparing-  it  with  the  living 
flora  it  liecomes  apparent  that  great  climatic  changes  must  have  taken  place 
since  the  close  of  the  Miocene  period  to  have  made  these  modifications  in 
plant  life  possible.  The  fossil  flora  embraces  about  1,50  forms  that  have 
been  distributed  among  33  natural  families.  Following  is  a  list  of  these 
families,  with  the  number  of  species  or  forms  referred  to  each:'' 


Species. 

Filices  10 

Equisetaccw 4 

Conifera' 13 

1 

1 

4 

1 

1 


Typhacecv 

Sparganiace.T 

Cyperacew 

Smilacew 

Miisacea' 

Juglandacea; 8 

Myricacea- 3 

Salicacew 10 

Betidacew 2 

Fagace* 15 

Ulmacea! 5 

Urticacew 10 

Magaoliace;i?   5 

Laurace;ii   12 


Species. 

I'latanaceiB 3 

Le{/mninos(v 5 

Aiiacardiaeea' 1 

Celastracea^ 4 

Aceracea' 2 

Sapindace;* 5 

lihamnacew 4 

Vitaceai l 

Sterculiacert' 1 

Credneriaceie 1 

Tiliaceit 2 

Araliacea' G 

Gornacew 2 

JEricacccv 1 

Ebenacew .<• 3 

01eace;e l 

Phyllites,  Cariiites 3 


'  The  orders  that  are  also  found  in  the  present  flora  are  printed  in  italics. 


774  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK, 

The  .excellent  Flora  of  the  Yellowstone  National  Park/  by  Mr.  Frank 
TAveedy,  has  been  made  the  basis  of  all  comparisons  between  the  fossil  and 
livino-  floras.  According  to  Tweedy,  the  present  flora  embraces  69  natural 
families,  273  genera,  and  657  species.  The  fossil  flora  embraces  33  families, 
63  genera,  and  148  species.  The  living  flora  has,  therefore,  4  genera  to 
each  order  and  2.4  species  to  each  genus,  while  the  fossil  flora  has  not 
quite  2  genera  to  each  family  and  2.3  species  to  each  genus.  The  relative 
proportion  between  the  families,  genera,  and  species  is  shown  to  be  approxi- 
mately the  same  in  the  Tertiary  and  the  living  floras.  A  still  further 
comparison  shows  tliat  there  are  a  fraction  more  than  twice  as  many  living 
as  fossil  families,  4.3  times  as  many  living  genera,  and  4.6  times  as  many 
species. 

On  con\paring  the  families  in  the  two  floras,  it  is  found  that  19  of  the 
33  fossil  families  are  not  represented  in  the  living  flora.  In  the  list  of 
families  above  given  the  ones  not  italicized  are  the  families  not  repre- 
sented at  the  present  time.  It  will  be  seen  that  such  important  families  as 
the  Juglandaceffi,  Fagacese,  Ulmaceai,  Magnoliacea;,  Lauracea?,  Platanacea?, 
Anacardiacea?,  Celastracefc,  Vitacete,  Sterculiaceai,  Tiliaeea;,  Araliacese, 
Ebenacea;,  and  Oleacese  are  not  represented  in  the  present  flora.  In  other 
words,  there  are  no  walnuts,  beeches,  oaks,  chestnuts,  elms,  magnolias, 
sycamores,  simiacs,  grapes,  lindens,  aralias,  persimmons,  or  ashes  at  the 
present  day.  The  absence  of  such  important  trees  and  shrubs  produces  a 
profound  modification  of  the  floral  surroundings. 

The  dominant  element  in  the  living  flora  consists  of  the  abundant 
coniferous  forests;  yet  only  8  species  are  represented,  and  of  these  only  5 
are  at  all  common,  and  65  per  cent  of  the  wliole  coniferous  growth  is  made 
up  of  1  species.  The  fossil  flora  is  represented  by  13  species,  or  nearly 
twice  as  many  as  the  living.  Among  them  was  a  magnificent  Sequoia  that 
was  closely  allied  to  the  living  Sequoia  sempervirem  of  the  Pacific  coast.  It 
had  trunks  10  feet  in  diameter  and  probably  of  vast  height.  There  were 
also  2  well-marked  species  of  Sequoia,  known  from  the  leaves,  and  a 
number  of  supposed  Sequoia  cones.  The  pines  were  also  abundant,  no 
fewer  than  8  species  having  been  detected. 

The  deciduous-leaved  trees  and  shrubs  of  the  Yellowstone  National 
Park  are  conspicuously  few  in  numbers.     There  are  2  species  of  Betula,  2 

1  WashiiigtdD,  1886,  pp.  1-78. 


FOSSIL  FLORA.  775 

of  Alims,  7  of  Salix.  2  of  I'opulus,  1  of  Acer,  4  of  Vacciniuni,  5  of  tlie 
order  Caprifoliacea',  2  of  Conuux'a>,  2  of  the  Koaaceje,  etc.  Perhaps 
the  most  conspicuous  tree  is  the  quaking  aspen  {Populus  trenmloides).  The 
Cottonwood  (I'.aH(fmtifoUa)  is  rare,  being  found  only  ah)ng  Caclie  Creek. 
Several  of  the  willows  are  abundant,  as  is  also  the  common  birc.li  (lirfiila 
(jlandulom),  and  the  June  berry  (AiiiclanrJiicr  almfolia).  The  other  shruljs 
are  rare,  or  are  confined  to  few  localities. 

The  fossil  flora,  on  the  other  hand,  was  especially  rich  in  deciduous 
leaved  vegetation.  Thus  the  Juglandacese  was  represented  by  5  species 
of  Juglans  and  4  species  of  Hicoria  (Carya),  a  number  of  which  were  very 
abundant.  The  g'enus  Populus  was  especially  rich,  there  being  no  fewer 
than  7  species.  Certain  of  these,  as  Populus  speciosa,  P.  (Japhnogemides,  and 
P.  f/landidifcra,  were  in  great  aliundance,  and  the  stratum  in  which  they 
occur  consists  of  a  perfect  mat  of  these  leaves.  Something  like  100  examples 
of  1  s])ecies  were  obtained. 

Another  striking  feature  was  the  presence  of  numerous  magnificent 
magnolias.     Of  these,  4  species  have  been  described  from  the  leaves  and 

1  from  the  thick  petals  of  the  flower.  The  species  described  as  Magnolia 
spectaUlis  is  represented  by  a  great  number  of  leaves  in  a  fine  state  of 
preservation.  It  appears  to  be  more  closely  related  to  the  living  M.  gran- 
dijiora  (M.  fmtida  of  later  authors)  than  any  one  previously  described. 

The  sycamores  were  also  an  important  element  in  this  flora.     Of  the 

2  species  described  from  the  leaves  and  1  from  the  wood,  the  one  known 
as  Platanus  gmlklmce  was  especially  abundant.  It  is  found  in  nearly  all 
the  Tertiary  beds  in  the  Park  and  is  represented  in  the  collections  by  nearly 
200  examples.  The  species  described  as  Plataninium  hagdeni  is  based  upon 
a  trunk  or  branch  6  inches  in  diameter.  It  is  most  closely  related  to  the 
living  Platanus  occidentaUs. 

Another  important  group  is  formed  by  4  species  of  Aralia.  Of  these, 
AraUa  notata  was  evidently  one  of  the  most  abundant  and  imposing  trees 
of  the  whole  flora.  The  collections  contain  over  100  examples,  none  of 
which  are  entire,  however,  as  some  of  the  leaves  must  have   been  fully 

3  feet  in  length  and  more  than  2  feet  in  width.  A  small  leaf  and  one  of 
medium  size  are  figured  on  the  plates.  Aralia  tvliitnegi,  a  species  common 
to  the  Auriferous  gravels  of  California,  had  striking  5  to  7  lobed  leaves, 
often  1  foot  in  length.      This  species  was  not  so  abundant,  judging  from 


776     GEOLOGY  OP  THE  YELLOWSTONE  NATIONAL  PARK. 

the  fossil  remains,  as  the  former  species,  but  it  was  apparently  quite  widely 
distril^uted.     The  other  species  had  smaller  3  or  5  lobed  leaves. 

The  family  Lauracese  was  strongly  represented  by  5  genera,  11  species, 
and  a  large  number  of  examples.  The  genus  Laurus,  which  is  now  exclu- 
sively an  Old  World  group,  was  represented  by  6  well-marked  species.  The 
genera  Malapoenna  or  Litsea  and  Cinnamomum,  other  Old  World  forms, 
were  both  represented,  the  former  by  2  and  the  latter  by  1  species.  The 
genus  Persea,  an  extensive  Old  World  genus,  with  species  also  in  tropical 
America  and  the  southern  United  States,  was  represented  by  1  species, 
which  is  closely  related  to  a  small  tree  now  living  in  the  South. 

Another  large  and  important  group,  now  entirely  uni'epresented  in  the 
Park,  is  the  Fagaceae,  embracing-  2  species  of  Fagus,  1  of  Castanea,  1 1  of 
Quercus,  and  1  of  Drj^ophyllum.  The  Fagus  here  described  is  a  lieautiful, 
characteristic  leaf  and  was  evidently  rare,  as  only  a  few  examples  were 
obtained.  The  Castanea,  on  the  other  hand,  was  very  abundant  and 
widely  distributed  within  the  Park.  The  leaves  are  large,  and  as  handsome 
and  striking  as  are  the  leaves  of  the  living  species.  The  oaks,  however, 
were  abundant  in  species  and  usually  in  individuals,  and  all  but  3  proved 
to  be  new  to  science.  Perhaps  the  most  marked  are  Qnercus  ycmcei/i, 
Q.  ciili-eri,  and  Q.  (/yossideiitatn. 

The  family  UrticacefE,  which  is  represented  in  the  living  flora  by  a 
single  rare  herb  (XJrtka  (fraciUs),  was  represented  during  Tertiary  times  by 
some  10  species  of  Ficus  and  a  single  more  or  less  doubtful  species  of 
Artocarpus.  Several  of  the  figures  are  represented  by  a  large  number  of 
specimens — as,  for  example,  Ficus  densifoUa — but  most  of  them  were  rare,  at 
least  as  evidenced  by  the  fossil  remains.  It  is  of  great  interest  to  learn,  how- 
ever, that  tliev  were  once  present  in  a  region  that  has  long  since  ceased  to 
support  them.  The  curious  leaf  referred  provisionally  to  Artocarpus  is 
also  of  much  interest  as  indicating  the  possible  presence  of  the  bread-fruit 
trees  in  this  portion  of  the  American  Continent.  Two  unmistakable  species 
of  Artocarpus  have  already  been  detected,  1  from  the  Laramie  and  Denver 
beds  of  Colorado,  and  the  other  from  the  Auriferous  gravels  of  California 
and  the  Miocene  of  Oregon.  It  is  therefore  not  improljable  that  this  t}'pe 
was  in  existence  in  the  Yellowstone  National  Park  during  the  early  Tertiary. 

The  family  Leguininosa?,  now  represented  b}'  a  host  of  small  herbaceous 
plants,   was   then    represented    by   3   species   of   Acacia  and    2   of  Legu- 


FOSSIL  FLORA.  777 

minosites,  but  the  fossil  forms  are  not  jjsirticularly  satisfactory.  The  forms 
rcfcn-ed  to  Acacia  consist  of  well-defined  pods  and  are  somewhat  con- 
ventionally I'eji'arded  as  representing  the  modern  Acacia.  No  leaves  were 
obtained  that  coidd  with  satisfaction  be  held  as  representing-  the  foliage 
of  these  pod-bearing  shrubs  or  trees.  The  2  species  of  Leguminosites  are 
supposed  to  represent  leaflets  of  some  leguminous  plant,  but  beyond  this 
it  is  not  possible  to  venture. 

The  only  remaining  group  of  deciduous-leaved  jdants  of  any  magni- 
tude is  tlie  Sapindaceai,  with  5  species  of  Sapindus.  One  of  these,  Sapiiuhis 
(ij/ii/is,  is  perhaps  the  most  abundant  form  found  among  the  Tertiar}' 
plants.  The  small  characteristic  leaflets  are  found  in  the  greatest  profusion. 
The  other  species  were  less  abundant. 

The  other  forms  that  require  mention  are:  Ulmus,  4  species;  Acer, 
at  least  2  species;  Celasti-us,  3  species,  and  Rharanus,  Paliurus,  Zizyphus, 
Cissus,  Pterospermites,  Tilia,  and  Rhus,  with  a  single  species  each. 

Tlie  vascular  cryptogams  appear  to  have  been  a  more  prominent 
feature  of  the  flora  during  Tertiary  times  than  at  present.  Of  the  2  families 
present,  the  Filices  and  Equisetacese,  the  former  is  represented  by  10  and 
the  latter  by  4  species,  while  the  living  flora  has  but  6  ferns  and  4  horse- 
tails, all  rare. 

The  ferns  were  evidently  abundant.  They  belong  to  6  genera,  and  are 
represented  in  several  cases  by  a  large  number  of  specimens.  The  largest 
genus  is  Asplenium,  with  4  species.  The  species  described  as  Asplenium 
magnum  is  one  of  the  largest  and  finest  forms  that  has  been  detected  out- 
.  side  of  the  Carboniferous.  Asplenium  idd'mgsl  is  also  a  large,  well-marked 
species.  The  genus  Dryopteris,  the  old  Aspidium,  is  represented  by  2 
species,  both  of  which  are  rather  rare.  They  are,  however,  botli  fruiting, 
a  condition  of  uncommon  occurrence  among  fossil  forms.  There  is  also  a 
beautiful  Woodwardia,  quite  closely  allied  to  a  species  now  living  in  the 
eastern  United  States,  and  fine  examples  of  the  widely  distributed  climbing 
fern  {Lygodium  kaulfusii).  The  only  living  North  American  species  (L. 
pahnatum)  is  found  from  Massachusetts  and  New  York  south  to  Kentucky 
and  Florida,  and  is  generally  rare  throughout  its  range.  The  other  ferns 
are  an  Osmunda  and  a  delicate  form  referred  provisionally  to  the  genus 
Devallia. 

The  genus  Equisetum,  although  represented  by  4  more  or  less  satisfac- 


778  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

tory  species,  was  not  abundant  or  particularly  important.  The  most  abun- 
dant form  {E.  Inif/Kci)  is  small  and  has  much  the  appeai'ance  of  the  living' 
E.  Vnuosum.  The  largest  form  (E.  microclontuni)  is  very  rare.  It  was 
al)(»ut  3  cm.  in  diameter. 

From  A\diat  has  been  presented,  it  is  obvious  that  the  present  flora  of 
the  Yellowstone  National  Park  has  comparatively  little  relation  to  the 
Tertiary  flora,  and  can  not  be  considered  as  the  descendant  of  it.  It  is  also 
clear  that  the  climatic  conditions  must  have  greatly  changed.  The  Ter- 
tiary fl(>r;i  appears  to  have  originated  to  the  south,  while  the  i)resent  flora 
is  evidently  of  more  northern  origin.  The  climate  during  Tertiary  time,  as 
made  out  by  the  vegetation,  was  a  temperate  or  subtemperate  one,  not  unlike 
that  of  Virg'inia  at  the  present  time,  and  the  presence  of  the  numerous  species 
of  Ficus  would  indicate  that  it  even  bordered  on  subtropical.  The  condi- 
tions, however,  that  permitted  the  growth  of  this  seemingly  subtropical  vege- 
tation may  have  been  ditferent  from  the  conditions  now  necessary  for  the 
growth  of  these  plants.  Thus,  the  genus  Dicksonia  is  at  present  a  tropical 
or  subtropical  genus,  yet  at  least  1  species  is  distributed  well  into  the  tem- 
perate region.  If  a  series  of  beds  should  be  discovered  in  which  there  were 
a  large  number  of  Dicksonias,  it  might  be  supposed  to  indicate  tropical  or 
subtroincal  conditions;  yet,  as  a  matter  of  fact,  these  species  may  at  that 
time  all  have  been  so  constituted  as  to  grow  in  a  temperate  land,  and  the 
genus  as  a  whole  may  have  become  tropical  in  recent  times.  Following 
out  this  general  line  of  argument,  it  may  be  said  that  while  the  Tertiary 
vegetation  of  the  Yellowstone  National  Park  would,  from  our  present 
standard,  be  regarded  as  indicating  a  temperate  or  possibly  warmer  climate, 
the  actual  conditions  then  prevailing  may  have  been  quite  different.  It  is 
certain,  however,  that  the  conditions  were  very  diff'erent  from  those  now 
j)revailing. 


Tahl(  sliiiiciiHi  till'  iliftrihiilinii  of  Ihe  Tciliarji  phdili  of  llif  YiUoirHlove  National  Park. 


779 


s.    S^M 

SO 


Species. 


IJistrilmtion  in  Tin-  I'ark. 


r)istril)iitiipn  mitside. 


Fort  Union  (Eocene). 


=  i^'S 


CD 


J5  o 


Woodwardia  jireareolat:!  n.  sp  .. 

Aspleniiim  indingsi  n.  sp 

Aspleninm  magnur  i  n.  sp 

AspK'niam  crosum  (Lx.) 

Asplenium  remotideiis  n.  sp 

Dryopteris  wcedii  u.sp 

Dryopteris  xantbolitheusis  n.  sp 

Devallia  ?  montana  n.  sp 

Lygodium  kaiilfusii  Heer?* , 

Osmimda  affinis  Lx 

Equisetum  liaguei  n.  sp 

Eqiiisctum  Icsiiuereuxi  ii.  sp 

Eqiusetum  caualiculatum  n.  ap... 

Eqnisptum  deciduum  n.  sp 

Piuus  gracilistrobus  u.  sp 

Pinuspremurrayaiia 

Pinus  macrolopis  n.  sp 

Pinus  sp 


so 


Pinus  wardii  n.sp 

Pinus  iddingai  n.}} 

Taxites  olriki  Heer 

Sequoia  couttsife  Heer 

Sequoia langsdorfii  (Brgt.)  Heer.. 

Sequoia,  cones  of 

Phragmites?  latissima  n.  sp 

Sparganium  stygiuni  Heer , 

Cyperacites  angustior  Al.  Br.  d 

Cyperacites  giganteus  n.  sp 

CyperacJtes  sp 

Cyperacites  sp 

Sniilax  laniarensis  n.  sp 

Musophyilum  complicatnm  Lx 

Juglans  ealifornica  Lx 

Juglans  rngosa  Lx 

a  The  numbers  refer  to  tbe  beds  in  wbirb  the  plants  were  found. 

&  Cherry  Creek,  Oregon. 


I 


Interraediftte 
(Miocene). 


a  f^ 


ai  )  W 


Lamar  Flora 

(Miocene). 


fes 

fsS 

•i|-l 

ta'r   t-'  « 

3"g-' 

^  « 

*    s 

ta 

a 

12. 


13. 


4.6,7      X 
5,0 


6 

I 

6  1... 


15. 


a    < 


I     I 


c  Kare. 
(i  Miocene;  Elk  Creek;  Lx. 


780     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  showhif/  the  dislrihiition  of  the  Tertiary  plants  of  the  Yellowstone  National  Park — Continued. 


Species. 


Distributiou  in  the  Park. 


Fort  T'niim  (Eocene). 


III  . 

=-  i  -J^  ^ 


;  o  I  >  0) ,   O 

a  o!p  P.:   « 


SS 


35. 

36. 
37. 
38. 
39. 
40. 
41. 
42. 
43. 
44. 
45. 
46. 
47. 
48. 
49. 
50. 
51. 
52. 
53. 
54. 
^5. 
56. 
57. 
58. 
59. 
60. 
61. 
02. 
63. 
04. 
65. 
66. 
67. 
68. 


•I    X 


Juglana  schimperi  Lx 

Jny,laus  LuiriloUa  n.sp  — 
Juglaus  cresceuti.i  ii.  sp  .  - . 
Hiroria  antiquii  (Newby.)  . 
Hicoria  eresoeutia  ii.  sp  — 

Hicona  culveri  n.  sj) 

^ly rica  scottii  Lx '  X 

Myrica  wardii  n.  sp  -- — 

Myrica  lamareusis  n.sp '  — 

Populus  glandalifera  Heer X 

Populus  speciosa  ^'avd X 

TopuUis  xautliolitbensie  n.sp X 

Populus  dapbnogenoides  "Ward,  .i  X 
Populus  balsamoidesGiippt  -- 

Populus  .'  vivaria  n.sp 

Salix  varians  Heer 

Salix  angusta  Al.  Br 

Salix  lavateri  Heer 

Salix  elongata?  O.  Web 

Betula  iddiijgsi  n..sp  

Corylus  macquarryi  Heer , 

Fagus  antipolii  Heer 

Fagus  undulatan.  sp 

Castanea  pulebella  n.  sp 

Quereua  grosideutata  n.sp 

Quercus  consirailis  ?  Xewby  . . . 

Quereus.'  niaguifolia  n.  sp 

Quercus  furcinervis  araericana 

Quercus  Tveedii  n.  sp 

Quercus  sp 

Quercus  olafseni  Heer 

QuercuB  yam-eyi  n.  3p 

Quercus  culveri  n.  sp 

Quercus  heaperia  11.  ap 

a  The  number.^  refer  to  the  beds  in  wbich  tbi^  plants  were  found. 


oi 

n 

ff 

fl 

CS 

t>^ 

O 

§ 

^ 

y 

c 

>^ 

•^ 

dO 

^ 

o 

a 

o 

M 

O 

Ph      1 

Intermediate 
(Miocene). 


.:  p^ 


3) 

o 

i^" 

o 

^ 

T 

t4 

-« 

O 

;ph     H  ifc<     w  i  ta 


4.  I  s. 


Lamar  Flora 
(Miocene). 


11. 


L.  S.  X 
M.S.  X 


5 
M.S.6 


13. 


■Distribution  out.side. 


'X! 


X? 


16. 


£     a 


17.  18. 


X 
X 

X? 


X?    X 


x» 


.     X 


b  Mioi-eiie  of  Alaska. 


FOSSIL  FLORA.  Jgl 

Table  ahqii-imj  the  dintrihiition  of  the  rirtiuiy  ptanta  of  the  yellowntom:  yutiomil  /'aii— Continued. 


Distribution  In  the  Park. 


Fort  UiiiiUl  (Koceiit;). 


Species. 


Dryopliyllum  longipetiolatum  n. 
sp 


70. 
71. 
72. 
73. 
74, 
75. 
76. 
77. 
78. 
79. 
80. 
81. 
82. 
83. 
84. 
85. 


Ulmua  pseudo-iulva .'  Lx  . . . 

TJlmus  minima  ?  "Ward 

Ulnius  rljamnifolia.'  Ward . 

I'lniits,  fruits  of 

Planera  longifolia  Lx 

ITii'us  di'iormata  n.  sp 

Ficusungeri  Lx 

Ficns  sp 

Ficiis  shastensis  ?  Lx 

Ficus  sordida  Lx ■..., 

Ficus  densi folia  n.  .sj) 

Ficus  liaguei  u.  sp 


-.5 -=8 


s  g 

II 


Intcrni(>diatu 
(Miocene). 


^    O 

-?      3 


1.      2.      3 


O    ,&< 


Lamar  Flora 
(Miocene). 


6.      7.      8. 


X 


Ficus  tiliiFfolia?  Al.  Br 

Ficus  asiminitfolia  Lx 

Artocarpus.'  quercoidos  u.  sp. 
ilagiiolia  califoriiica  Lx 

86.  Magnolia  spoctabilis  n.  sp 

87.  Magnolia  micropliyila  n.  sp  ... 

88.  Magnolia  culveri  u.  sp 

89.  Magnolia?  poUardin.sp 

90.  Laurus  priraigenia  .'  I'ng 

91.  Laurus  perdita  u.  sp 

92.  Laurus  montana  n.  sp 

93.  Laurus  priiiceits  Heer 

94.  LauruB  californica  Lx 

95.  Laurus  grandis  Lx 

06.  Persea  pseudo-carolinensis  Lx 

97.  Malapoenna  lamarensisn. sp.. 

98.  Malapoonna  cuneatau.sp 

99.  Cinnanionium  spectabilia  Heer 
100.  Platanus  guillelmai  Gopp , 

a  Tlu>  numbers  refer  to  the  beds  in 


J 


ifeO 


S2 

4^  O 


Distribution  outside. 


M.S. 


X 
M.S.  3 
3 


3,5,6 
3,5,7 


,v? 


1.5,6,7      X 
which  tlic  plants  were  found 


IG. 


17 


18. 


X  ?  D.  L.  X  I 


782  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Table  showiiiii  the  disiribiition  of  the  Tertiai-y  plants  of  the  Yelloivstoiie  Xational  ParA'— Continued. 


Species. 


101 
102. 
103. 
104. 
105. 
106. 
107. 
108. 
100. 
110. 
111. 

112. 
113. 
114. 
115. 
]'6. 
117. 
118. 
119. 
120. 
121. 
122. 
123. 
124. 
125. 
126. 
127. 
128. 
129. 
130. 
131. 
132. 
133. 


Platanus  nioutana  u.  sp 

Acacia  macroapernia  li.  8p 

Acacia  lamareusis  n.  ap 

Acacia -n^ardii  u.  sp '.-. 

Legnmiii()3ite.s  cassioides  Lx... 
Lt'guminoaiteslamareusisu.  sp. 
Kbiis  mixta  ?Lx 


Distribution  in  thi*  I'ark. 


Fort  T'uion  (Eocene). 


^ 

o 

^^ 

"e 

S    £ 

o 

S^ 

-    ,; 

a?  M 

.-  c- 

^         >H 


1'^ 


im 


a  s  5  o 


9  2  S  5 

K  00       ' 


ft 


Celastru3  cnlveri  ii.  sp 

Celastrus  injequalis  ii.  sp 

Celasti'iis  ellipticus  u.  sp 

E1,T  0(1  end  roil    poly  morpli  urn 

AVard , 

Acer  vivariniii  u.  sp 

Acer,  fruit  of j 

Sapindus  afiinis  Xewby 

Sapiudus  alatus.'  Ward 

Sapiudiis  grandifoliolns  \^iard6. 
Sapiudus  graiidifolioloides  n.  ap. 

Sapindiis  vanlii  u.  sp , 

Kharanus  reetiner\  is  Lx 

Paliurus  colouibi  Heer 

Zizyphus  serrulatus  Ward 

Cissus  hagiiei  n.  sp 

Pterospermites  hagnei  n.  sp 

Credueria  .'  pachyphylla  n.  sp 

Tilia  popnlifolia  Lx 

Grewiopsis?  aldersoni  n.  sp 

Aralia  wrightii  u. sp..  

Aralia  notata  Lx 

Aralia  serrulatan.  sp 

Aralia  wliitueyi  Lx 

Aralia  sp 

Conius  newberryi  Holliclv 

Cornus  wrightii  d.  sp 

a  The  numbers  reler  to  tiie  beds  in  wliich  the  plants  were  found. 


Intermediate 
(Miocene). 


K     W 


8.      9. 


.. 


Lar.iar  Flora 
(Miocene). 


Distribution  outside. 


-4^       •  .       • 


!S 


to  I       2 


rS^S 


'ts 


5  -^.S    § 
■a    -^    ■= 

Sura      ^ 


p=(      :5 


5 
3,7 


M.S.X 


13.    14. 


>        3 

S    1 


16.  ,17.  18. 


X    D.L  X 


h  Also  ou  the  Thumlerer. 


FOSSIL  FLORA.  783 

Table  b/ioici'ii;/  thr  tlUtiibittion  of  tin:  Terl'uirn  jilaiitu  of  the  Yilluiixtoiic  National  Park — Cuutiuued. 


MK 

Distributiui 

iu  the  V 

ark. 

Distributiou  outside. 

Fort  I'nio 

K-eut')- 

Iiitenui'diato 
(Mioceue). 

Lamar  Flora 

(Miocene). 

til 
a 

1 

o 

c 
'> 

O 

g 

1 

Species. 

o 

s 

« 

®  = 

c  c 
c  = 

C 

■S   O 
«!      - 

=  £ 

c 

1 
3. 

03 

r 

s 

CS 

t- 
2 

1 

o 

4. 

§ 

c 

6 

u 

o 

03 
lU 

1 

1 

S 

t-i 

.2  a:* 

o  o 

>s 

p  V. 
es  o 

11 
g 

O 

1 

a 

£ 

1 

O 

1 

o 
c_ 

o 

j 

5 

o 

1 
s 

c 

09 

£ 

o 

•3 

5 
ti 

a 

ii 

|l 

En  o 

^  Si 
o 

1 

3 

1 

O 

-  * 

n 

P. 

i 

to 
n 
o 

'3 
1 

a 

3 

g 

s 

a 
O 

,5 

'5 

'Z 
> 

to 

1 

1.      2. 

5. 

G. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

16. 

17.  i  18. 

X 

.    _ 

4 

X! 

X? 

X? 

X 

-> 

1 

138.  Ffiisiuus  wri"htii  n.  sp X 

139.  Pbyllites  craasitblia  n.  sp 

X 

X 

X 
V 

i 

142.  Sequoia  magnitica  u.ey.h 1 

X 

X 

145.  Lauriiioxylou  pulcbellum  u.  ap.. 

X 

146.  Perseosylim  aroinaticum  Felix. 

::::.;;;:: 

148,  Rhamnacinium  radiatuui  Felix  . 

149.  Quercinium  laniarense  ii.  sp 



1 

150.  Quercinium  kuowltoni  Felix 

X? 

aThu  numbers  refer  lo  the  beds  iu  which  the  plants  were  fouud. 


b  Up  Cache  Creek. 


GEOLOGICAIi  COXSIDKRATIOX  OF  THE  TERTIARY  FEORA. 

Naturally  the  geological  aspects  of  this  fossil  flora  are  considered  as  of 
paramount  importance,  for  it  was  to  ascertain  the  liearing  of  the  plants  on 
the  question  of  geological  age  that  this  investigation  was  undertaken.  As 
I  have  already  pointed  out  under  the  section  devoted  to  the  biological 
asjjects  of  the  flora  (p.  775),  a  A'ery  large  jjroportion  of  the  plants  were 
found  to  be  iiew  to  science,  and  therefore  could  have  onlj'  limited  value  in 
determining  the  age,  but  enough  previously  described  forms  were  lecog- 
uized  to  warrant  certain  deductions.  It  is  the  purpose  to  set  these  con- 
clusions forth  in  this  section. 


784  GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Tlie  first  plants  brouglit  back  from  this  portion  of  the  YelloAvstore 
National  Park  by  the  early  Hayden  survey  parties  were  submitted  to  Prof. 
Leo  Lesquereux,  and  although  few  in  number  the  specimens  and  species 
were  nevertheless  sufficient  to  afford  some  indication  of  their  age.  Pro- 
fessor Lesquereux  regarded  the  plants  from  Elk  Creek  and  vicinity  as 
indicating  an  Eocene  age,  and  those  from  the  well-known  Fossil  Forest  on 
the  west  side  of  the  Lamar  Valley  as  closely  allied  to  those  of  the  Aurif- 
erous gravels  of  California.  It  is  a  pleasure  to  state  that  this  adumbration 
has  been  abundantly  confirmed  by  the  results  of  more  searching  study  of 
a  larger  amount  of  material,  but  at  the  time  this  was  outlined  the  facts  were 
so  few  that  the  suggestions  were  not  regarded  as  conclusions,  and  as  it  was 
before  any  careful  detailed  geological  work  had  been  done,  these  now  clearly 
defined  horizons  came  to  be  grouped  together  under  the  somewhat  non- 
committal term  Volcanic  Tertiary. 

Although  the  geology  of  the  region  has  been  fully  discussed  by  Mr. 
Arnold  Hague  in  Part  I  of  this  monograph,  it  seems  necessary,  for  the  satis- 
factory understanding  of  the  problems  requiring  solution,  to  set  forth  briefly 
the  geological  features  characterizing  this  portion  of  the  Park  which  have 
a  direct  bearing  upon  the  remarkable  flora  found. 

In  the  first  place,  all  the  material  constituting  the  beds  in  which  the 
Tertiary  plants  are  embedded  is  of  volcanic  origin.  According  to  the  geol- 
ogists, this  material  may  be  divided  into  two  distinct  periods  of  volcanic 
eruption,  which  may  be  distinguished  by  their  mineral  composition. 

The  older  series  of  these  la^'as  has  been  designated  as  the  early  acid 
breccias  and  flows,  and  the  younger  as  the  early  basic  breccias  and  flows. 
Both  these  series  of  rocks  carry  plant  remains.  In  general  the  matrix  in 
which  the  plants  are  preserved  is  a  fine-grained  ash,  probably  deposited  as  a 
mud  flow,  with  all  the  appearance  of  stratification  and  other  indications  of 
water-laid  deposits.  Occasionally  the  material  is  much  coarser  and  has  the 
appearance  of  breccias  mixed  with  fine  sediments.  The  acid  rocks  are 
usually  light  in  color — yellow,  lavender,  or  gray — while  the  basic  rocks, 
which  carry  more  iron,  are  darker  in  color — frequently  some  shade  of  green 
or  dark  brown,  passing  over  into  black.  In  some  instances,  as  might  be 
expected  with  fine  water-laid  beds,  the  deposits  in  both  series  of  lavas 
closely  resemble  one  another,  while  the  great  mass  of  lava  of  the  two 
bodies  may  be  readily  distinguished.     The  acid  breccias,  the  oldest  of  the 


FOSSIL  FLORA.  785 

lava  flows,  rest  in  many  places  upon  the  upturned  eflj^es  of  Arcliean  and 
Paleozoic  locks.  In  most  instances  the  basic  breccias  either  rest  directly 
upon  the  acid  rocks  or  else  the  underlying  rocks  are  not  exposed.  The 
acid  breccias  are  found  on  both  banks  of  tlie  Yellowstone  River  near  the 
mouth  of  Elk  Creek,  and  near  the  junction  of  the  Yellowstone  River 
with  Hellroaring-  Creek,  as  well  as  on  Crescent  Hill  and  near  the  head 
of  'l\)wer  C^reek. 

In  the  neighborhood  of  Lost  Creek,  and  on  the  northern  end  of 
S]iecinien  Ridge,  along  the  drainage  of  Crystal  Creek,  the  basic  breccias 
are  known  to  lie  directly  upon  the  acid  breccias.  In  these  localities  the 
floj-a  has  a  character  distinctly  its  own,  and  bears  evidence  of  being  younger 
than  the  flora  from  the  acid  breccias.  The  basic  series  of  rocks  is  typified 
at  the  Fossil  Forest,  and  also  at  the  cliff  a.  short  distance  to  the  south  and 
east  of  the  Fossil  Forest.  They  occur  also  on  the  east  bank  of  Lamar 
River,  between  Cache  and  Calfee  creeks.  All  of  these  localities  are  char- 
acterized by  their  plant  remains,  and  the  following  determinations  of  age 
are  fully  wan-anted. 

The  table  of  distribution  of  Tertiary  plants  in  the  Yellowstone  National 
Park  has  been  prepared  for  the  pmpose  of  showing  in  a  graphic  manner 
the  distribution  of  the  various  plants  within  the  limits  of  the  Park  and  the 
affinities  of  those  having  an  outside  distribution.  From  this  it  appears  that 
the  Tertiary  flora  consists  of  150  more  or  less  satisfactory  species.  Of 
this  number,  81  species,  or  over  50  per  cent,  are  here  described  for  the  first 
time.  New  species  can  not,  of  course,  have  the  value  in  determining  age 
that  previously  described  forms  have,  but  when  their  general  facies  as  well 
as  close  affinities  are  taken  into  account,  they  also  become  of  positive  value. 
On  eliminating  the  81  new  species,  together  with  8  forms  not  specifically 
named,  there  remain  61  species  upon  which  we  must  depend  in  the  deter- 
mination of  the  ages  of  the  various  strata  in  which  they  are  contained. 

A  further  examination  of  the  table  brings  out  the  fact  that  this  flora 
may  be  naturally  divided  into  3  more  or  less  distinct  subfloras  or  stages. 
These  three  divisions  are  the  older  or  acid  series,  the  intermediate  series, 
and  the  basic  or  younger  series.  The  first  division  (acid)  has  a  flora  of  79 
species;  the  second  (intermediate)  a  flora  of  30  species,  and  the  third  (basic) 
a  flora  of  70  species.  It  further  appears  that  23  species  or  forms  are 
common  to  two  or  more  of  the  divisions. 

MON  XXXII,  PT  II 50 


78(5  GEOLOGY  OF  THE  YELL0WST02TE  KATIO:jfAL  PARK. 

The  floi'a  of  the  older  or  acid  series  will  be  first  considered.  Of  the 
79  species,  42  are  either  new  to  science  or  not  specifically  named,  leaving 
37  species  having  a  distribution  beyond  the  limits  of  the  Park.  Following 
is  a  list  of  these  species: 

Aspleuium  erosum  (Lx.).  Uliiius  rbauinifolia  Ward, 

Lygodiuiii  kaulfusii  (Heer).  Ficus  uugeri  Lx. 

Taxites  olriki  Heer.  Ficus  asiminrefolia  Lx. 

Sequoia  couttsite  Heer.  Laurus  primigenia  ?  Uiig. 

Sequoia  laiigsdorfii  (Brgt.)  Heer.  Laurus  priuceps  Lx. 

Sparganium  stygium  Heer.  Laurus  californica  Lx. 

Cyperat'ites  angustior  AI.  Bi-.  Laurus  grandis  Lx. 

Musopbyllura  tomplicatum  Lx.  Ciunamoinuin  spectabilis  Heer. 

Juglans  rugosa  Lx.  Plataiius  guilleliuiii  Gopp. 

Juglans  schimperi  Lx.  Legnminosites  cassioides  Lx. 

Myiica  scottii  Lx.  Sapiudus  aflim's  Lx. 

Populus  glandulifera  Heer.  Sapiudus  alatus  Ward. 

Populus  speciosa  Ward.  Sapiudus  grandifolius  Ward. 

I'opulus  dapbnogeuoides  Ward.  I'aliurus  colouibi  Heer. 

Salix  lavateri  Heer.  Zizypbus  serrulatus  Ward. 

Fagus  autipofii  Heer.  Tilia  populifolia  Lx. 

Quercus  consimilis  Newby.  Aralia  notata  Lx. 

Quercus  olafseni  Heer.  Cornus  uewberryi  Rollick. 

These  37  species  have  the  following  distribution:  Five  are  found  in  the 
coal-bearing  Laramie,  5  in  the  Denver  and  Livingston,  17,  or  nearly  50  per 
cent,  in  the  Fort  Union,  9  in  the  Green  River  group,  and  11  in  the  Aurifer- 
ous gravels  of  California.  Of  the  species  common  to  the  acid  rocks  and 
the  Laramie  at  Denver  and  Livingston  beds,  not  one  is  found  exclusively  in 
these  beds,  but  they  are  such  species  as  Sequoia  langsdorfii,  Juglans  rugosa, 
Platanus  guillelmce,  and  Juglans  schimperi,  which  enjoy  a  wide  geological  and 
geographical  distribution. 

The  Fort  Union  element  in  this  flora  is  a  very  important  one ;  in  fact, 
it  may  be  called  the  dominant  element.  It  includes  at  least  12  species  that 
have  never  before  been  found  outside  of  the  type  locality.  Among  these 
are  Sparganium  stygium,  Populus  speciosa,  Populus  daphnogenoides,  Uhnus 
minima,  Ulmus  rhamnifolia,  Sapiudus  affinis,  Sapindus  grandifoliolus,  and 
Cornus  newberryi.  Some  of  these  are  represented  by  as  many  as  200  indi- 
viduals, showing  that  they  existed  in  great  abundance,  as  they  are  also 
known  to  have  existed  at  the  mouth  of  the  Yellowstone.     This  abundance 


FOSSIL  FLORA.  787 

also  makes  their  determination  certain.  Several  other  species,  having  a 
wider  distribution,  are  very  abundant  in  these  beds,  such  as  Aralia  notafci, 
which  is  represented  by  more  than  100  specimens,  and  Sequoia  lanf/sdorjii, 
which  has  a  wide  distribution,  but  is  most  abundant  in  this  country  in 
the  Fort  Union  beds.  Sequoia  couttsice,  having  a  somewhat  wide  range,  is 
also  very  abundant  in  the  beds  under  consideration  and  the  Fort  Union. 
Besides  these  are  a  number  of  species  that  can  not  be  mistaken,  as  Zizyphus 
serrulatus,  Taxites  olriki,  etc. 

One  species,  Asplenhim  erosum,  has  been  found  in  both  Lai-araie  and 
Denver  strata  in  Colorado.  It  is  represented  by  only  2  or  3  small  and 
more  or  less  doubtful  examples  from  the  Yellowstone  below  Elk  Creek. 
JiKjhms  rugosa  is  a  species  of  wide  distribution  and  therefore  of  compara- 
tively little  value  stratigraphically.  It  is  found  from  the  Laramie  to  the 
Miocene,  but  is  rare  in  the  acid  beds  within  the  Park.  Quercus  olafseni  has 
been  found  in  the  Laramie,  but  its  determination  in  the  Park  depends  on  a 
single  doubtful  fragment  from  the  vicinity  of  Elk  Creek. 

The  species  that  have  also  been  found  in  the  Green  River  beds  are 
comparatively  unimportant.  Lygodium  kaulfusii  is,  in  this  country,  a  typical 
Green  River  species.  It  is  rare  in  the  acid  series,  but  abundant  in  the  basic 
series  along  the  Lamar  River.  Musophyllum  complicatwn  has  never  before 
been  reported  outside  of  the  Green  River  beds.  Fkus  ungeri  and  Tilia 
2>o])uUfolia  are  typical  Green  River  plants,  but  are  represented  here  by  one 
or  two  examples  each. 

The  species  found  in  the  Auriferous  gravels  are  the  only  ones  remaining 
to  be  considered.  Of  the  11  species,  Juglans  rugosa,  Quercus  hreweri,  Salix 
lavateri,  and  Quercus  olafseni  are  open  to  doubt,  as  they  are  represented  by- 
only  one  or  two  fragments  each.  Ficus  asimin'KpfoUa  likewise  depends  upon 
a  single  leaf,  but  it  is  a  well-preserved  one,  and  the  determination  is  probably 
correct.  Aralia  notata,  another  of  the  species,  is  very  rare,  if  really  found 
at  all,  in  the  Auriferous  gi-avels.  The  three  remaining  species  are  rela- 
tively abundant,  and  there  is  little  question  as  to  the  correctness  of  their 
determination. 

The  species  whose  distribution  lies  beyond  the  limits  of  the  Park 
having  been  passed  in  review,  it  will  be  of  interest  to  note  the  obvious 
affinities  of  certain  of  the  more  important  new  forms.  Thus,  Asplenium 
remotidens  is  closely  related  to  A.  erosum^  and  Dryopteris  weedii  and  D.  xantho- 


788     GEOLOGY  OF  THE  YELLOWSTONE  NATIONAL  PARK. 

Utliensis  to  Lastrea  goMlanum,  both  of  wliicli  are  abundant  in  the  Denver 
beds  of  Colorado.  Juglans  crescentia  is  related  to  J.  nigella,  as  identified  by 
Professor  Ward  in  the  Fort  Union  group.  The  beautiful  new  Populus 
xanthoUthensis  is  very  close  to  P.  genatrix  of  Newberry,  from  the  Fort 
Union  group.  Betula  iddingsi  is  obviously  related  to  B.  prisca;  Quercus 
yanceyi  to  Q.  laimfolia;  Platanus  montana  to  P.  raynoldsii;  Celastrus  ctdveri 
to  C.  ovatns  and  C.  curvinervis ;  and  Sapindus  grandifolioloides  to  S.  grandi- 
foUohis,  all  of  the  Foi-t  Union  group. 

From  this  evidence  it  appears  that  the  flora  of  the  eai-ly  acid  breccias 
in  the  Yellowstone  National  Park  finds  its  closest  affinity  with  the  flora  of 
the  Fort  Union  group,  and  it  is  unhesitatingly  referred  to  that  age.  The 
relation  of  this  flora  to  that  of  the  Laramie  is  unimportant,  being  confined 
to  less  than  half  a  dozen  species.  Its  relationship  to  the  Denver  and  Green 
River  floras  is  naturally  closer,  but  it  forms  only  a  small  element  of  these, 
as  also  with  the  flora  of  the  Auriferous  gravels  of  California.  The  relation, 
as  based  on  total  number  of  species,  is  unimportant,  but  in  the  upper  beds 
it  beffins  to  show  a  transition. 

It  will  be  next  in  order  to  consider  the  intermediate  flora.  As  already 
stated,  this  embraces  30  species,  of  which  number  16  are  confined  to  these 
beds  and  14  are  distributed  outside,  either  in  the  acid  or  basic  series  or 
beyond  the  limits  of  the  Park.  A  further  analysis  brings  ovit  the  fact  that 
of  the  16  species  peculiar  to  these  beds  13  are  regarded  as  being  new  to 
science,  and  of  the  14  species  found  beyond  the  limits  of  these  beds  5  are 
new  to  science.  This  makes  a  total  of  18  species  that  are  regarded  as  new, 
leaving  12  species  having  a  distribution  without  the  Park.  Following  is  a 
complete  list  of  these  12  species: 

Osmunda  afifinis  Lx.  Laiirus  grandis  Lx. 

Sequoia  langsdorfli  (Brgt.)  Heer.  Platanus  guillelmse  Gopp. 

Juglans  rugosa  Lx.  Elseodeudron  polymorpbum  Ward. 

Ulmus  minima  Ward.  Sapindus  affinis  Lx, 

Ficus  tilijefolia  Al.  Br.  Aralia  notata  Lx. 

Laurus  californica  Lx.  Aralia  wbitneyi  Lx. 

Four  of  the  species  above  enumerated  (Sequoia  langsdorjii,  Juglans 
rugosa,  Platanus  guillelmce,  and  Aralia  notata)  have  a  wide  distribution,  being 
found  from  the  Laramie  to  -the  Upper  Miocene,  and  are  therefore  of  com- 
paratively little  value.     One"  of  the  remaining  (Osmunda  affinis)  is  found  in 


FOSSIL  FLORA.  739 

the  Denver  beds;  3  are  confined  to  the  Fort  Union,  and  6  species  are  found 
in  the  Auriferous  gravels  of  CaHfornia. 

Of  the  5  new  species  found  in  other  beds,  2  are  common  to  the  ohler 
or  acid  series  and  3  to  the  younger  or  basic  series.  It  therefore  becomes 
apparent  that  this  flora,  although  reasonably  distinct,  finds  its  greatest 
affinity  with  the  younger  or  basic  series.  This  is  shown  by  the  species 
connnon  to  the  intermediate  series  and  the  Auriferous  gravels  and  by  the 
new  species  connnon  to  the  basic  series.  This  is  not  especially  pronounced, 
and  could  hardly  be  made  out  for  the  intermediate  flora  as  a  whole,  were  it 
not  for  certain  species  that  come  from  rocks  that  are  directly  succeeded  by 
the  basic  rocks.  For  these  reasons  it  was  at  first  supposed  that  a  part  of 
the  localities  represented  belonged  to  the  lower  and  a  part  to  the  upper 
beds,  but  by  combining  several  of  these  this  intermediate  flora  was  worked 
out.  But,  as  stated  above,  the  rocks  of  this  series  that  are  known  to  be 
the  lowest  bear  a  flora  nearest  to  that  of  the  acid  rocks,  and  the  rocks 
known  to  be  higher  hold  plants  most  neariy  related  to  those  of  the  upper 
or  younger  beds. 

It  now  remains  to  consider  the  flora  of  the  basic  breccias  and  its 
relationships.  The  typical  locality  for  this  flora  is  the  Fossil  Forest  and 
vicinity,  including  the  locality  on  the  east  side  of  the  Lamar  River,  between 
Cache  and  Calfee  creeks.  This  flora,  as  a  whole,  embraces  70  species  or 
forms,  distributed  as  follows:  38  species  new  to  science,  3  forms  not  spe- 
cifically named,  and  29  species  having  a  distribution  beyond  the  limits  of 
the  Park.  Following  is  a  list  of  the  species  having  an  outside  distribution: 
Lygodium  kaulfusii  Heer.  Ficus  sordida  Lx. 

Sequoia  langsdorfli  (Brgt.)  Heer.  Ficus  asiminiefolia  Lx. 

Juglans  californica  Lx.  Magnolia  calif.irnica  Lx. 

Juglans  rugosa  Lx.  Laurus  californica  Lx. 

Hicoriaantiqua(Newby.)Kn.  Laurus  primigenia?  Ung. 

Populus  balsamoides  Gopp.  Laurus  grandis  Lx. 

Saiix  variaus  Heer.  '  Persca  pseudo-carolinensis  Lx.      ; 

Sahx  angusta  Al.  Br.  Platanus  guillelma3  Gopp. 

Sahx  elongata  Heer.  ruus  mixta  Lx. 

Corylus  macquarryi  (Forbes)  Heer.  EL-eodendron  polymorphum  Ward. 

Quercus  furciuervis  americaua  Kn.  Sapiudus  graudifolius  Ward. 

Ulmus  pseudo-fulva  Lx.  Ehamnus  rectinervis  Lx. 

Planera  lougifolia  Lx.  Aralia  notata  Lx. 

Ficus  shastensis  ?  Lx.  Aralia  whitneyi  Lx. 


790  GEOLOGY  OF  THE  YELLOWSTONE  NATTONAL  PARK. 

Of  these  29  species,  only  4  have  been  found  in  the  true  Laramie.  These 
^re  Juglans  rugosa,  Flatanas  guillelmcB,  Bhamnus  redinervis,  and  Diospyros 
brachysepala,  the  last  open  to  doubt.  All  of  these  species  have  a  wide  ver- 
tical range  and  are  consequently  of  little  value  in  indicating  age.  The 
affinities  of  this  flora  with  that  of  the  Laramie  may  therefore  be  regarded 
as  unimportant. 

The  relationship  of  this  flora  with  the  Fort  Union,  Denver,  and  Green 
River  groups  is  also  relatively  unimportant.  There  are  7  species  found  in 
each  of  these  groups,  but  none  are  confined  to  the  Denver,  and  only  1  to 
the  Green  River,  and  3  to  the  Fort  Union.  The  rest  are  of  wide  geograph- 
ical and  geological  distribution. 

The  relationship  of  the  flora  of  the  basic  rocks  is  clearly  with  that  of 
the  Auriferous  gravels  of  California,  for  no  fewer  than  17  of  the  29  species 
are  common  to  the  two  localities,  and  12  of  the  s^jecies  are  exclusively  con- 
fined to  them.  These  are  such  important  species  as  Aralia  tvMtneyi,  Persea 
pseudo-car olinensis,  Laurus  californica,  Laurus  grandis,  Magnolia  californica, 
Ficm  sordida,  Juglans  californica,  Rhus  mixta,  etc.  Most  of  these  are  present 
in  numbers  in  the  Park  flora,  and  there  can  therefore  be  no  question  as  to 
the  correctness  of  their  identification. 

Besides  the  species  above  enumerated  that  have  actually  been  found 
common  to  the  two  localities,  the  numerous  new  species  are  in  many  cases 
unmistakably  related  to  species  known  only  from  the  Auriferous  gravels. 
Thus,  Magnolia  culveri  is  close  to  M.  californica,  and  Magnolia  spectabilis  is 
so  close  to  M.  lanceolata  that  Lesquereux  so  identified  it.  Other  examples 
might  be  given,  but  they  are  unnecessary.  The  preponderance  of  evidence 
points  to  the  similarity  of  age  between  the  flora  of  the  basic  series  and  that 
of  the  Auriferous  gravels  of  California.  The  fixing  of  the  exact  age  of  the 
Auriferous  gravels  is  not  a  difficult  matter.  They  were  at  first  supposed  to 
be  Lower  Pliocene  in  age,  but  the  latest  evidence,  derived  from  a  more  or  less 
complete  restudy  of  the  abundant  flora,  together  with  a  thorough  investiga- 
tion of  the  stratigraphy,  makes  it  reasonabl}^  certain  that  it  is  really  Upper 
Miocene.  This  is  the  view  taken  in  the  present  instance,  and  this  flora  in 
the  Yellowstone  National  Pai-k  is  referred  to  the  Upper  Miocene: 

Asplenium  idclingsii  n.  sp.  Magnolia?  pollardi  u.  sp. 

Lygodium  kaulfusii.  Laurus  primigenia?  Ung. 

Equisetum  caualiculatum  n.  sp.  Laurus  californica  Lx. 


FOSSIL  FLORA. 


791 


Equisetum  ilecidmini  n.  sj). 
Sequoia  laugsdorUi  (Bigt.)  Ueer. 
Juglans  rugosa  Lx. 
Juglans  crescentia  n.  sp. 
Castanea  pulcbella  n.  sp. 
Ficiis  clensifolia  u.  sp. 
Ficus  asimiuffifolia  Lx. 


Laurus  gI•andi^s  Lx. 
Litsea  lamarensis  n.  sp. 
Platanus  guillelma;  Giipp. 
ELTodeudron  polymorphum  Ward. 
Sapiiidus  graiidifoliolus  Ward. 
Sapindus  wardii  n.  sp. 
Aralia  notata  Lx. 


Some  of  these  species,  as  Lygodium  kaulfusii,  Castanea  pulchella,  Laurus 
grandis,  Platanus  guillelmce,  Sapindus  grandifoUolus,  and  Aralia  notata,  are 
important  well-marked  species  that  have  weight  in  showing  the  close 
relationships  between  the  floras  of  the  two  series;  but,  on  the  other  hand, 
the  perfect  distinctness  of  the  beds  is  shown  by  the  fact  that  there  are  some 
40  species  that  are  confined  to  each  horizon.  It  will  not,  therefore,  be 
difficult  in  future  to  determine  the  horizons  of  the  various  plant-bearing 
beds  within  the  Yellowstone  National  Park. 

In  order  to  show  how  remarkably  distinct  these  three  floras  are,  it  will 
be  necessary  only  to  consider  the  species  in  common  between  them.  As 
already  stated,  only  23  forms  out  of  the  total  of  147  forms  are  common  to  two 
or  more  of  the  series  of  beds.  It  will  not  be  necessary  to  present  a  complete 
list  of  these  species  in  common.  The  numerical  results  show  that  8  forms 
only  are  common  to  the  three  beds,  2  to  the  acid  and  intermediate,  and  3  to 
the  intermediate  and  basic,  and,  finally,  that  10  are  common  to  the  acid  and 
basic.  When  these  facts  are  presented  in  connection  with  the  total  flora  of 
each  series,  the  diff"erences  become  even  more  marked.  Thus,  the  lower  or 
acid  series,  with  a  flora  of  79  species,  has  only  20  species  common  to  the 
others.  Of  these,  8  are  common  to  all  three  beds,  2  to  it  and  the  interme- 
diate beds,  and  10  to  it  and  the  upper  or  basic  beds.  The  intermediate 
beds,  with  a  flora  of  30  species,  have  13  species  in  common  with  the  others. 
Of  these,  8,  as  above  stated,  are  common  to  all  three,  2  to  intermediate  and 
acid,  and  3  to  intermediate  and  basic.  The  basic  or  j^ounger  beds,  with  a 
flora  of  70  species,  have  20  species  common  to  the  others.  Of  these,  it  is 
hardly  necessary  to  repeat,  8  are  common  to  all  three,  3  to  it  and  interme- 
diate, and  10  to  it  and  acid.  These  3  floras  are,  therefore,  shown  to  be 
markedly  distinct,  and  it  will  not  be  difficult  to  distinguish  them  in  future. 


PLATE  LXXVII. 


793 


PLATE    LXXVTI. 

Page. 

Figs.  1, 2.  Asple.vium  haguei  u.  sp.     Wolverine  Creek 655 

3, 4.  Trapa  ?  MiCROPH YLLA  Lx.     Wolverine  Creek 661 

5.  Sequoia  LANGSDORFii?  (Brgt.)    Heer.    Wolverine  Creek 657 

6.  QUERCUS  ELLisiANA  Lx.     Mount  Everts 659 

7-9.  Paliurus  minimus  n.  sp.     Wolverine  Creek 659 

10.  Viburnum  ROTUNDIFOLIUM  Lx.     Wolverine  Creek 662 

11-15.  Onoclea  MiNi.MA  u.  sp.     Wolverine  Creek 656 

794 


U.  8.  0£OUXUGAL  SURVEY 


MONOORAPri  XXXII      PART  II      PL.  LXXVII 


-  ■••« 


^ 

1 

i 

1 

1 

1 

! 

..1 

1 ,-. 
1, '    ■ 

1 

\     ■■  J 

\ 


LARAMIE    FORMATION. 


PLATE   LXXVIII. 


795 


PLATE    LXXVTII. 

Pajie. 

Fig.  1.  DoMBEYOPSis  PLATANOiDE.s  Lx.     ilouut  Evcrts 661 

2.  ViBUKN'UM  ROTUNDIFOLIUM  Lx.     Wolverine  Creek 662 

3.  Paliurus  zizYPHOiDEs?  Lx.     Wolverine- Creek 660 

4.  Myrica  bolanderi?  Lx.     Mount  Everts 658 

5.  Phragmites  falcata  n.  sp.     Mouut  Everts - 658 

6.  Fraxinus  DENTICULATA  Lx.     Mouut  Everts 662 

7.  Phyllites  sp.     Mount  Everts 662 

8,9.  Viburnum  rotundifolium  Lx.     Wolverine  Creek 662 

796 


U.   8.   OEOLOOICAL  SURVEY 


MONOORAPH  XXXII      PART  II      PL.    LXXVIIt 


LARAMIE   FORMATION. 


PLATE   LXXTX. 


797 


PLATE  LXXIX. 

Page. 

Fia.  1.  WoomvARDiA  PHEAREOLATA  n.sp.     Crescent  Hill 665 

2,3.  Asi'LENiUM  IDDINGSI  D.sp.     Yellowstone  River  below  Elk  Creek 666 

4.  Devallia?  MONTANA  u.sp.     Fossil  Forest 671 

5-8.  ASPLENIUM  MAGNUM  11.  sp.     Yellowstone  River  below  Elk  Creek 667 

8a.  Eularged  piumiles  of  tig.  8 667 

798 


U.  8.   OEOLOGICAC  SURVEY 


HONOORAPM  XXXII       PART  M       PL.    LXXIX 


PLATE    LXXX. 


799 


PLATE    LXXX. 

Page. 

Figs.  1,2.  Lygoditm  kailfusii  Heer.     I.amav  Kiver 672 

3.  Lygodilm  kaulfusii,  fruit.     Lamar  Kiver 672 

4,5.  OsMUNDA  AFFiNis  Lx.     Hill  above  Lost  Creek 673 

6.  AsPLENiUM  EROSUM?  (Lx.)  Kn.     Yellowstone  River  below  Elk  Creek 668 

7.  Asi'LEXiUM  RE.MOTIDENS  n.  sp.     Yellowstone  River  below  Elk  Creek 669 

8.  Dryopteris  WEEDii  n.  sp.    Yellowstone  River  below  Elk  Creek 669 

9,10.  ASPLENIUM  iDDiNGSin.  sp.     Yellowstoiie  Rlver  below  Elk  Creek 666 

11.  Pixus  MACROLEPis  n.  sp.     Fossil  Forest 679 

12.  PiNUS  GRACILISTROBUS  n.  sp.     Fossil  Forest 676 

800 


U.   8.   OEOLOUICAL  SURVCV 


MONOOKAPH  xxxri      PAHr  II       PL.    LXXX 


TERTIARY. 


PLATE   LXXXI. 


801 
MON  XXXII,  PX  II 51 


PLATE    LXXXI. 

Page. 

I'lG.  1.  DiiYOi'TERis  ZANTiiOLiTUENSi;  n.  sp.     Fossil  Forest 671 

2.  Dryopteris  webdii  n.  sp.     Yellowstone  Kiver  lielow  Elk  Creek 669 

3,  4.  Eqiisetum  haguei  ii.  sp.     Hill  above  Lost  Creek 674 

5.  Equisetum  deciduum  11.  sp.     Yellowstone  Kiver  below  Elk  Creek 676 

0.  Equisetum  caxaliculatum  ii.  sp.     Yanceys  Fossil  Forest 675 

7.  Equisetum  canaliculatum  u.  sji.    Specimen  Riclse 675 

8.  Sequoia  sp.     Fo.ssil  Forest 683 

9.  Magnolia?  POLLARDi  n.sp.    Fossil  Forest  Ridge 721 

10.  Magnolia?  POLLARDi  n.  sp.     Yellowstone  Elver  below  Elk  Creek 721 

802 


U.   a.   GEOLOGICAL  SURVEY 


MONOCRAPH  XXXIl      PART  II      FL.    LXXXI 


,T- 


^  r 


/      ,  \  '^ 


i"~% 


10 


TERTIARY. 


PLATE   LXXXII. 


803 


PLATE    LX  XXII 

Page. 

Fig.  1.  Taxiths  oi.riki  Heer 680 

2.  Sequoia  LAXGSDORrii  (Brgt.)  Heer 682 

3.  Taxites  olriki?  Hoer 680 

4.  Taxites  olri  ki  Heer.     Yellowstone  River  below  Elk  Creek 680 

5.  PiNUS  PREMOKRAYANA  11.  sp.     East  of  Yellowstone  Lake 677 

6,  7.  Sequoia  sp.    Fossil  Forest 683 

8,9.  PiNUS  IDDINGSI  u.  sp.     West  of  Duuraven 680 

10.  Cypebacites  GiGANTEUS  n.  sp.     Yellowstone  Eiver  bclow  Elk  Creek 684 

804 


U.  9.  CEOLOOICAL  SURVEV 


MONOGRAPH  XXXII      PAHT  »      PL.    LXXXII 


PLATE   LXXXIII. 


805 


PLATE    L  XX  XII  I. 

Page. 

Fig.  1.  MusopnYLLUM  complicatum  Lx.    Crescent  Hill 686 

2,3.  JUGLANs  LAURIFOLIA  n.  sp.     Vanceys  Fossll  Fotest 688 

4.  Cyperacites  sp.    Fossil  Forest 684 

5.  Phragmites?  LATissiMA  n.  sp.    Crescent  Hill 683 

6.  Cyperacite.s?  sp.     Crescent  Hill 6S5 

7.  HicoRiA  cuLVERi  u.  sp.     YellowBtone  Eiver  below  Elk  Creek 691 

806 


U.   8.   OEOLOGICAL  8URVEV 


MONOGRAPH  Xxxll      PAHT   II       PL.    LXXXIK 


">, 


K 


n 


'S 


I      ::l 


'     < 


3 


TERTIARY. 


PLATE  LXXXIV. 


807 


PLATE    LXXXIV. 

Page. 

Fiu.  1.  PopuLUS  GLANDTiLiFEHA  Heer.     Yellowstone  River  bplow  Elk  Creek 694 

2.  PoPULUs  DAPHNOGENOIDES  Ward.     Yellowstone  River  below  Elk  Creek 69n 

3.  PoPULUS  SPECiosA  Ward.     Yellowstone  River  below  Elk  Creek 694 

4.  Myrica  WARDii  u.  sp.     Fossil  Forest 692 

5.  Myhica  lamarensis  u.  sp.     Lamar  River 693 

6.  Myrica  scottii  Lx.     Yellowstone  River  below  Elk  Creek 692 

7.  HicoRiA  CRESCENTIA  n.  sp.     Crescent  Hill 690 

8.  JuGLANs  CRESCENTIA  D.  sp.     Crescent  Hill 689 


U.    S.    GEOLOGICAL  SURVEY 


MONOGRAPH  XXXII      PART  II      PL.    LXXXIV 


TERTIARY. 


PLATE   LXXXV. 


809 


PLATE    LXXXV. 

Page. 

Figs.  1,2.  Popuu-s  xamtholithensis  ii.  sp.     Yellowstoue  River  below  Elk  Creek 695 

3.  Salix  variaxs  Heer.     Lamar  River 697 

i,  5.  Fagi'.s  UNDULATA  u.  sp.     Yellowstone  River  below  Elk  Creek 700 

810 


U.  8.  oeOLOaiCAL  6URVEY 


MONOGHAHM  XXXH       PART  II       PL.    LXXXV 


TERTIARY. 


PLATE   LXXXVI. 


811 


PLATE    LXXXVI. 

Page. 

Fig.  1.  PoPULUs  liALSAMOiDES?  Gtipp.    Fossil  Forest 696 

2.  PopULUsf  VIVARIA  u.  sp.     Fossil  Forest 696 

3.  CORYLUS  MACQUARRYi  Heer.    Fossil  Forest 699 

4,5.  Betula  iDDiNGsi  n.  sp.    Yellowstone  River  below  Elk  Creek 698 

6-8.  Castanea  rui.CHELLA  n.  sp.     Fossil  Forest 702 

812 


U.   6.   OEOLOOtCAL  SuRVCY 


MONOGRAPH  XXAII       PART   I)      I'L.    LXXXVl 


TERTIARY, 


PLATE   LXXXYII. 


813 


PLATE    LXXXVII. 

Page. 

Figs.  1-3.  Cast.\nea  puixhell.v  u.  sj).     Fossil  Forest 702 

4.  QuiiKcrs  WEEDii  u.  sp.     Fossil  Forest 705 

5.  QuERcrs  CULVERI  n.  sp.     Yello-nstoue  River  l)elow  Elk  Creek 708 

6.  QuERCls  coxsiMiLis?  Newby.     Yello-n-stone  River  below  Elk  Creek 704 

7.  QuERCUS  GHOSSIUENTATA  n.  sp.     Fossil  Forest - 704 

814 


0.   «.   GEOLOGICAL  SURVEY 


MONOGRAPH  XXXII       PM-T  It      PL.    LXXXVtl 


PLATE   LXXXVIII. 


815 


PLATE    LXXXVIII. 

Page. 

Fig.  1.  QUERCUS?  magnifolia  n.  sp.     Yellowstone  Rivur  below  Elk  Creek 70-1 

2.  Ulmus  PSEUDO-FULVA?  Lx.    Laiuiir  River 711 

3,4.  Ulmus,  KUUITS.     Yellowstone  River  below  Elk  Creek 712 

5.  QUERCUS  FURCiNERVis  AMKRiCAXA  Kn.     Fossil  Fovest 705 

6,  7.    DRYOPH  YLLUM   LONGIPETIOLATUM   U.  sp 710 

816 


U.   S.   OfOLOOtCAL  8URVCV 


MONOGRAPH  XXXII      PAHT  tl      PL.    LXXXVIII 


PLATE   LXXXIX. 


817 
MON   XXXII,  PT   II 52 


PLATE    LXXXIX 


Page. 

FlO.  1.    FiCUS   DEXSIFOLIA  n.  sp 714 

2.  QuERCUS  YANL'Evi  u.  sp.     Yunceys  Fossil  Forest 707 

3.  Ficus  sp.     Yellowstone  Eiver  below  Elk  Creek 713 

4.  Leguminosites  lesqleiuexiana  Kn.     Crescent  Hill 730 

5,6.  Legumixosites  i.amakensis  n.  sp.     Lamar  Eiver 731 

7.  Quehcvs  sp.     Yellowstone  River  below  Elk  Creek 707 

818 


U,  0.  UEOkOaiCAL  SURREY 


MONOailAPH  XXXK       PAFIT  II      PL.    LXXXIX 


TERTIARY. 


PLATE   XC. 


819 


PLATE    XC. 

Page. 

Figs.  1,2.  Ficus  densifolia  n.  sp 7U 

3.  Ficus  haguei  n.  sp.    Fossil  Forest lio 

4.  Fraxinus  WRiGHTii  n.  sp 753 

820 


U.   6,   OeOLOlilCAL  SURVEY 


MONOGRAPH  XXXII      PART   PI       PL.   XC 


TERTIARY. 


PLATE   XCI. 


821 


PLATE    XCI. 


Fig.  1.  Ficus  densifoi.ia  u.  sp 714 

2.  Ficus  deformata  n.  sp.    Yellowstone  River  below  Elk  Creek 712 

3.  Ficus  ungeri  Lx.    Yellowstone  River  below  Elk  Creek 713 

4,5.  Laueus  primigenia?  Ung 722 

822 


u.  9.  oEOLooicA.  suflvev 


MONOGHAPH  XXXII      PA.IT   II       PL.    XCI 


PLATE  XCII. 


823 


PLATE   XCII. 

Page. 

Fig.  1.  Artocarpus?  quercoides  n.  sp.     Yellowstone.  River  Vielow  Elk  Creek 716 

2-4.  Malapoenna  cuneata  n.  sp ''^t! 

5.  Magnolia  culvbri  u.  sp.     Lamar  River ^...       "20 

824 


U.    8.    QEOLOGICAL  SUhVCV 


MONOQRAPH  XXXII      PART  II      PL,   XCII 


TERTIARY. 


PLATE  XCIII. 


825 


PLATE    XCIII. 

P«ge. 

Figs.  1,2.  Magnolia  spectabilis  n.  sp.     Fossil  Forest 718 

3.  LAunus  GRAXDis  Lx.     .Specimen  Ridge 725 

4,5.  Malapoenn'a  LAMAREXSis  n.  sp.     Lamar  Eiver 726 

826 


U.   S.   GEOLOGICAL  SURVEY 


MONOuHAPM   XXXM       PAHf    II       PL.    XCIII 


PLATE  XCIV. 


827 


PLATE    XCIV. 

Figs.  1-6.  Laurus  perdita  n.  sp.     Near  Yaneeys  Fossil  Forest 723 

6.  ClNNAMOMUM  SPECTABILE  Heer.     Tower  Creek 727 

828 


u.  8.  aeoLObicAL  sunvEv 


MONOGRAPH  XXXtl      PAHT  U      PL.   XCIV 


PLATE  XCV. 


829 


PLATE    XCV. 

Page. 

Fig.  1.  LAunus  GRANDis  Lx.     Specimen  Ridge 725 

2.  Laurus  MONTANA  n.  sj).     Yellowstone  River  below  Elk  Creek 724 

3.  Laurus  puinceps  Heer.     Yellowstone  River  below  Elk  Creek 725 

4.  PeRSEA  rSEUDO-CAROLINEXSIS  Lx 725 

5,6.  DiosPYRos  LAMARENSIS  n.  sp.     Specimen  Ridge 751 

830 


U.  0.  OeOkOCICAL  fURVEV 


MONOGRAPH  XXXII      PADT  H       PC.   KCV 


TERTIARY, 


PLATE  XCVI 


831 


PLATE    XCVI. 

Page. 

Fig.  1.  Platanus  guillelm^  Gopp.    Fossil  Forest 727 

2,3.  Platanus  MONTANA  n.  sp.     Hill  above  Lost  Creek 728 

4.  DiosPYROS  LAMARENsis  D.  sp.     Lamar  River 751 

5.  Malapoknna  LA.MARENSIS  u.  sp.     Lamar  Kiver .• 726 

832 


U.    6.   OCOLOaiCAL  SURVEV 


MONOf^flAPH  XXXII       PART  II       PL.    XCVl 


PLATE  XCVII. 


MON   XXXII,  PT   II .J3 


833 


PLATE    XCVII. 

Page. 

Fig.  1.  El.eodendron  roLYMOUPiiUM  AVanl.     Yancey  Fossil  Forest 734 

2.  Arctostaphylos  elliptica  u.  sp.     Yellowstoue  River  beli)W  Elk  Creek 750 

3.  Celastrus  ELLiPTicus  11.  8p.     Yellowstone  River  below  Elk  Creek 734 

4.  Celastrus  culveri  n.  ap.     Yellowstone  River  below  Elk  Creek 732 

5.  Platani'S  Gl'iLLBLM.E  Giipp.     Yellowstoue  Kiver  below  Elk  Creek 727 

834 


U.    8.    OEOLOGlCAL  SURVCV 


MONOOHAPH  XXKll       PART  II      PL.    XCVli 


TERTIARY. 


PLATE  XCVIII. 


835 


PLATE     XCVIII. 

Page. 

Fios.1.2.  SAriNDis  WAUDii  11.  sp.     Yellowstone  River  below  Elk  Creek 738 

3.  C'Ei.A.sTRCs  iN.Eyu.\ns  u.  sp.     Yellowstoue  Eiver  below  Elk  Creek 733 

4.  Acer  viVAUiuM  n.  sp.    Fossil  Forest 735 

5.  ACEH,  ERiiT.     Crescent  Hill -•  ■  ^^'' 

6.  Acacia  lamarensis  n.  sp.     Lamar  River 730 

7.  Acacia  wardii  n.  sp.     Fossil  Forest.. 730 

8.  Acacia  macrosperma  u.  sp.     Fossil  Forest 729 

83U 


U.   «.   OEOLOCICAU  ftUflVEV 


MONOGRAPH   XXXir      PART  II      PL.    XCVIII 


PLATE  XCIX. 


837 


PLATE     XCIX. 

Page. 

Fig.  1.  Sapindus  gkaxdifoliolu.s?  Ward 737 

2.  Sapixdus  grandifoliolus  Ward 737 

3.  Arali A  wniTNEYi  Lx.     Fossil  Forest  Kidge 748 

4.  rTEROSPEKMiTES  HAGUEi  n.  sp.     FossU  Forest  Ridge 742 

5.  Sapindu.s  wardii  d.  sp.     Fossil  Forest 738 

S38 


U.   a.   OEOLOCiCAL  8URVEV 


MONOGRAPH   XXXII       PART    II       PL.    XCIX 


PLATE   C. 


830 


PLATE     C. 

Pnge. 
Fig.  1.  Aralia  notata  Lx.     Yellowstone  River  below  Elk  Creek 745 

2.  Sai'indus  grandifolioloides  n.  sp.     Hill  above  Lost  Creek 738 

3.  DlosPYROS  HAGUEi  u.  sp.     Yellowstoue  River  below  Elk  Creek 752 

840 


PLATE  CI. 


841 


PLATE     CI. 

Page. 

Fig.  1.  Akali  V  whightii  n.  sp.     Fossil  Forest 744 

2.  CissiTEs  iiAGUKl  II.  sp.     Fossil  Forest 741 

3.  AUALIA  SKRRULATA  n.  sp.     Vellovrstouo  River  Ijelow  Elk  Creek 747 

4,5.  Zizynius  SERRULATA  Ward.     Yellowstone  River  below  Elk  Creek 740 

6.  Credneuia?  pachyphylla  n.  sp.     Yellowstone  River  below  Elk  Creek 742 

7.  Pai.iurus  colombi  Heer.     Head  of  Tower  Creek 740 

842 


U.    8.   GEOLOQlCAL  8URV(V 


MONOflRAPM  XXXir      PART  ll      PL.   Cl 


TERTIARY. 


PLATE    CII. 


843 


platp:  cii. 

Page. 
Figs.  1-3.  Sapindus  afkinis  Newby.     Yellowstone  River  below  Elk  Creek 736 

4.  Sapindus  GRANDiFOLioLus?  AVaiil.    Yellowstone  River  below  Elk  Creek 737 

5.  Phyllites  CRASSiFOLiA  u.  sp.    Fossil  Forest 753 

844 


U.   6.   GEOLOGICAL  8URVEV 


fclONOOnAPH  XXXII      PART  II      PL.    Clt 


PLATE    cm. 


845 


PLATE    cm. 

I'agp. 

Fig.  1.  Phyi.lites  ckassifolia  ii.  sp.     Speciiiieu  Ridge  Forest 753 

2.  PnYLLiTES  sp.     Yellowstone  Kiver  below  Elk  Creek 753 

3.  Caepites  pedunculatus  u.  sp.     Yellowstone  River  below  Elk  Creek 755 

4,5.  CORNUS  WRiGHTii  11.  Sp.     Fossil  Foiest 749 

6.  CoRxis  XEWBERKYi  Hollick.     Y'ellowstonc  River  below  Elk  Creek 749 

846 


J.    8.  QEOLOOICAL  fiURVfV 


PLATE    CIV 


347 


PLATE    CIV. 


iSE(JUOIA  MAGXII'ICA  II.  sp. 

848 


Page. 
671 


U.   d.   OEOLO:>1CAL  SURVEY 


MONOGRAPH  XXXll      PART  II      PL.  CIV 


SEQUOIA    MAGNIFICA. 


PLATE   CV. 


849 
MON   XXXII,  PT   II 54 


PLATE    CV. 


Sequoia MAGNiFiCA  n.  sp. 
850 


Page. 
761 


U.    8.    GlcOLOCICAL  SURVEV 

1 

MONOGRAPH  XXXll      PART  II      PL.   CV 

.V    / 

Jb. 

l 

i 

t  - 

-^^^^y                  "'-                       ^^^^^1 

I 

|B  jL 

^^^S^^^       ^  fll^^^F 

HHyl^B 

^^^^i^diflH^Mw^lt^^^^^^^H 

^^^^^^^H 

mp^ 

" 'M^^E^g^^^^^^^^^H 

M 

^^^■I^^^^^^^^^^H 

I^^Bg^-;;'^;;^.':  "^    ■-';>:-;:'^^?-'.;y>'^.;*;< 

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^1 

SEQUOIA    MAGNIFICA. 


PLATE   CVI. 


851 


PLATE    CVI. 

Page. 
PiTYOXYLON  ALDERSOM  11.  8p 763 

852 


U.  ft.  CEOLOO'CAL  8URVEV 


MONOGRAPH  XXXII      PART  II      PL.  C«l 


PITYOXYLON    ALDERSONI. 


PLATE   CVII. 


853 


PLATE    CVII. 


PlTYOXYLON   AMETUYSTINUM  n.  Sp 
854 


Page. 
764 


U.   6.   OEOLOGtCAL  8URVEV 


MONOGRAPH  XXXll      PART  II      PL.    CVII 


^v^MM|||HHH| 

&• 

'^^^^^^^^^^^^^B 

* 

1 

^V^v    ■  lit        . 

•V.  s 

^P>' 

■k:4^" 

1 

H^ii  - 

^^B 

^sM^ 

^k- 

t 

.*i- 

Vi 

^B 

• 

• 

^B'^ 

i 

^                             -        ■  •  -■  ■  ^ 

-.■^ 

^^^p^Pi^H 

1 

]:            ^                     '    ^ 

h. 

'm 

^-' 

^  «^ii- .  ~ 

i 

PITYOXYLON    AMETHYSTINUM. 


PLATE   CVIII. 


855 


PLATE    CVIII. 

Pttj;e 
PlTYOXYLON    AMETHYSTINUM  U.  Bp '''-* 

856 


PLATE   CIX. 


857 


PLATE    CIX. 

Page. 
PiTYOXYLON   ALDERSONI  n.  Sp 763 

858 


PLATE   ex. 


PLATE    ex. 


Sequoia  m agxifica  n .  sp 

Transverse  section  through  annual  ring.     Magnitieii  100  lUameteis. 

860 


Page. 
761 


U.   8.   OEOLOOICAi.   NUHvf. 


MONOr.RAPM   XXXll       PART   l<       PI.    CX 


SEQUOIA    MAGNIFICA. 


PLATE    CXI. 


861 


PLATE    CXI. 

Page. 
SeQVOI A   MAGNIFICA  U.  8p 7G1 

Transverse  section  through  one  annual  and  two  smaller  rings  of  growth.     Magnified  100 
diameters. 

862 


U.    8.    OEOLOGICAL  8UnvEY 


MONOGRAPH   XXXII       PART    II       PL      CX 


SEQUOIA    MAGNIFICA. 


PLATE   CXII. 


863 


PLATE    CXII. 

Page. 
PriYOXYLOX   ALDERSONI  U.  sp 763 

Transverse  section  in  summer  wood,  showing  large  resin  passage.    Magnified  100  diameters. 
864 


U.   8.   OEOLOOICAL  SUnvfY 


MONnr.MAPH  yxxw      part  li      PL.  Cxil 


PITYOXYLON    ALDERSONl, 


PLATE    GXIII. 


865 
MON    XXXII,  PT    II 55 


PLATE    CXIII. 

Page. 
PlTYOXYLON  ALDEKSONI  11.  Sp _ 753 

Loiirritudiiial  tauiiential  section.     Maguified  100  diauieters. 
866 


U.    S.    GEOLOGICAL   SUflVF 


II       PL.    CXIII 


PITYOXYLON    ALOERSONI, 


PLATE  GXIV. 


867 


PLATE    CXIV. 

Page. 
PiTYOXYLON   AMETIIYSTIXUM  11.  SJ> 764 

Transverse  section  passing  nearly  tliroiigli  one  aimual  ring.     Multiplied  100  diameters. 
SG8 


U.   8.   GEOLOGICAL  SURVEv 


MONOGRAPH    >i<"H       PART    II       PL      CXIV 


PITYOXYLON    AMETHYSTINUM. 


PLATE  CXV. 


869 


PLATE    CXV. 

Page. 
PlTVOXYLOX  AMUTIIYSTINTM  11.  sp "64 

Transverse  section  tlaougli  lall  and  spriug-  wood,  and  showing  large  resin  duet.     Magnified 
100  diameters. 

870 


U.    8.   QEOLOCICAL  SURV£ 


lOIRAPH   XXMI       fiVHT    II       PL      CK 


PITYOXYLON    AMETHYSTINUM. 


PLATE  CXVI. 


871 


PLATE    CXVI. 

Page. 
LaUI!INOXYI,ON  PULCHRUM  U.  81) '"^ 

Longitmliual   tangential   section,  showing    woiiil    cells,   medullary  rays,  and   large   duct. 
Magnilied  100  diameters. 


U.  a.  OEOLOaiML  auRVEV 


MONOGRAPH   XXXII       PART    II       PL.    CXVI 


LAURINOXYLON    PULCHRUM. 


PLATE  CXVII. 


873 


PLATE    CXVII. 

Figs.  1-5.  Seqtoia  ji.vgxikica  n.  sp 

1.  Tangential  section    X    ilO  di.amcterg.     .Shows  AVdod  cells,  uicdnllary  rays,  and   resin 

tube  of  short  sutiare-walled  cells. 

2.  Radial  section  X  00  diameters.     Shows  wood  cells,  with  a  single  series  of  pits,  long 

uieduU.ary  rays,  and  resin  tnlie  with  dark  contents. 

3.  Radial  section  X  00  diametei-s.     Shows  wood  C(dls  in  vicinity  of  annu.al  ring,  .sm.all 

pits  in  one  or  two  rows,  and  niednllary  rays. 

4.  Radial  section  x  00  diameters.     Shows  annual  ring,  with  fall  and  spring  cells  and 

medullary  rays. 

5.  Tangential  section  X  00  diameters.     Shows  wood  cells,  medullary  rays,  and  resin  tuhe 

with  dark  contents. 

.874 


Pago. 
761 


0.    8.   QtOLOGlCAi.  SUHVfv 


MONOGRAPH  KXXIt      PART  II      PL.   CXVll 


11 

1 

1 

■' 

IJfi 

_ 



— 

i 



0 
G 

o 
o 
o 
o 

1 

■  — ■  — ■ 

. 

• 

SEQUOIA    MAGNIFICA 


PLATE   CXVIII. 


875 


PLATE    C  XVI II. 

Page. 

Fiiis.1,2.  PiTYOXYLOS  AMETiiYSTiNTM  II.  sj)-     Specimen  Kidge 764 

3,4.  PiTYOXVLON  ALDEKsoNi  11.  sp.     Speciuieu  Ridge 763 

5.  QuERciNiUM  LAMAUEXSi;  n.  sp.  Spcciuien  Eidge 771 

6,7.  Rhamnacinium  radiatum  Felix.     Speciuien  Ridiie 769 

1.  Radial  section   X  90  diameters.      Shows   wood   cells   with   single  row  nt'   pits,  and 

spring  and  fall  wood;  also  medullary  rays. 

2.  Tangential  section  X  90  diameters.     Shows  the  long  wood  cells  and  sliort  medullary 

rays. 

3.  Radial  section  X  00  diameters.     Shows  wood  cells  with  a  single  row  of  pits. 

4.  Transverse  section  through  annual  ring,  x  00  diameters. 

5.  Transverse  section  x  320  diameters.     Shows  the  fall  and  spring  wood. 

6.  Transverse  section  X  90  diameters.     Shows  medullary  rays  of  short  cells,  thin-walled 

wood  cells,  and  scries  of  ducts. 

7.  Tangential  section  X  90  diameters.     Shows  wood  cells,  medullary  rays,  and  dotted 

ducts. 

876 


U.    S.   QEOLOOICAL  SU 


MONOGRAPH  XXXII      PART  II      PL.   CXVlll 


0 

o 

- 

0 

1 

o 

1 

1     \     1 

_ 

\     ■- 

\    1     1 

1 

1 

\ 

1 

PLATE    CXIX 


877 


PLATE    ex  IX. 

Page. 

Fid.l.   RiiA.MNAClxiUM  RADIATUM  Felix.     Specimen  Kidge 769 

'2.  PrrvoxYi.ox  ALDERSOXI  n.  sp.     Specimen  Ridge 763 

3-5.  Lai'RIXOXYlon  I'ULCHKUM  u.  sp.     Fossil  Forest 7(i5 

1.  Radial  section  x  90  diameters,  showing  wood  cells,  medullary  rays  ot'  short  cells,  and 

large  ducts. 

2.  Trausverse  section  x  320  diameters,  passing  through  an  annual  ring. 

3.  Radial  section  X  90  diameters,  showing  narrow  wood  cells,  large  plate  of  medullary  rays 

of  short  cells,  and  large  dotted  ducts. 

4.  Radial  section  of  reolariforiii  iluct  X  320  diameters. 
0.   Radial  section  of  dotted  duct  X  320  diameters. 

»78 


U.   8.   GEOLOGICAL  SURVEY 


MONOI.ftAPH    XX^II        PAHT    II        PL.    CXIX 


uxtoa 


5 


n 


TTTTT 


r-/  i  r  / 'n 


PLATE   CXX. 


879 


PLATE    CXX. 

Page. 

Fk;.  1.   Laurinoxvlox  pulchrum  ii.  sj).     Fossil  Forest 765 

2.  QuERcixiUM  i.AMAREXSE  11.  sj).     Speciiueu  Ridge 771 

3-5.  Pi,atax'in'u':m  iiaydeni  Felix.     Specimen  Ridge 7157 

1.  Transverse  sectiiiii  x  90  diameters,  sliciwing  wood  cells  of  two  kinds,  luednllary  riiys,  and 

large  ducts. 

2.  Transverse  section  X  320  diameters,  tlirougb  duet. 

3.  Tangential  section  x  90  diameters,  showing  wood  cells,  scalaril'orm  ducts,  and  very  large 

medullary  rays. 

4.  Transverse  section  x  90  diameters,  showing  short-celled  medullary  rays  with  black  cell 

contents,  wood  cells  in  vicinity  of  annual  ring,  and  numerous  large  ducts. 

5.  Radial  section   x  90  diameters,  showing  narrow  wood  cells,  numerous  ducts,  and  short- 

celled  medullary  rays. 

880 


U.    *     QfOLOOICAL  ttUHVtV 


MONOGRAPH   XXXll      PART  ll      PL.   CXX 


TERTIARY. 


PLATE    CXXI. 


MON    XXXII,  PT    H ,")6 


881 


PLATE    CXXI. 

Page. 

Figs. 1,2.  Qiercixiu.m  la.viarenseii.si).     Speeiiiien  Ridge 771 

3,4.  Smilax  i.AMABENSis  11.  sp.     Lauiiir  River : 785 

1.  Trausverse  section  x  90  diameters,  sliowing  thick-walled  wood  cells,  immense  ducts, 

and  usnnlly  single-celleil  medullary  rays. 

2.  Tangential  section  x  90  diameters,  showing  wood  cells,  and  large  and  small  medullary 

rays. 

882 


U.    S.    GEOLOGICAL  SURVCV 


inONOORAPH  XX.'-.W      PART   II      PL.   Cxx 


INDEX. 


NumbLTs  in  iVa'ii-  are  those  nf  pajjes  on  which  ilkistrationa  (plates  or  fijjures)  appear;  numbers  in  black-fucrcl  typo 
are  thoHO  of  ]>ii»res  on  wliich  fossils  are  dpscribed  iu  detail. 


^V. 


ra;; 


057 


AbietitesdubiusLi.  es.p 

Absaroka  Kange,  analyses  of  rocks  of 272 

Absarokites,  nualyses  of 83,329,352 

cLnracter  and  occurrence  of 328-339 

photomicrographs  of 332 

Absarokite-sboshouite-banakite  rocks,  character  and 

occurrence  of 326-355 

Acacia  lamarensis  n.  sp 730,  SSO 

Acacia  macrosperma  u.  sp 7*29t  S36 

Acacia  microphy Ua  Heer ■  730 

Acacia  wardii  u.  sp 730,836 

Acambona  osagensis  Swallow 56U 

AceraccjT?,  description  of  species  of 735-736 

Acer,  fruit  of 736,  SSO 

Acer  vivarium  n.  sp 735-736,  S30 

Acer  trilobatum  productum  Heer  735 

Acer  trilobatum  tricuspidutum  Heer 736 

Acrotreta  attenuata  Meek 449 

Acrotreta  gemma  Billings 449,472 

Acrotreta  pyxidicula  White 449 

Acrotreta  subconica  Meek 449 

Actinostroma  sp 496-497 

Actinocriuus  viaticus 488 

Agnostus  bideus  Sleek 455,  474 

Aguostus  interstrictus  White 454-455,  474 

Agnostus  josephus 455 

Agnostus  tumidosusH.  &.  W 455,474 

AUanite,  occurrence  of 402 

AInus  carpiuoides  Ls 699 

Alum  Creek,  obsidian  near 388 

Analy&es  of  rocks.  61,65,  70,  81.  83, 116, 163,  260,  261, 263, 272. 325 

Amethyst  Monutain,  fossil  forest  on 757-753 

Ammonites  henry i  M.  and  H 631 

Ammonites  placenta  De  Kay 640 

Amnicola  (?)  cretacea 633, (/■4.S 

Auacardiacea?,  descriptions  of  species  of 731 

Auatiua  (Cercomya)  punctata  n.sp 6'48-6189,'j46' 

Anatina  (Cercomya)  sp 629 

Andesite,  character  of 4, 73-82, 122 

occurrence  of 4, 24  J-246,  314-321 

photomicrograph  of sao 

Andesite-porjihyry ,  characters  of 16,  94-97 

occurrence  of 10. 12, 19,  2i),  21,  24.  42,  43,  45,  46,  47,  52,  59 

photomicrographs  of OJ,  104 

Andesitic  breccia,  occurrence  of 4,56,  270-274 

Andromeda  grayana  Lx 661 

Anemia  subcrelacea  (Sap.)  Gard.  andEtt 657,058 

Auisotrypasp 516-517 

Anomia  propatoris  "White 037 

Anomia  sp 6^7 


Page. 

Anoiiiites  scabriculus  Norwood  and  Pralten 531 

Anoniites  semireticulatus  Martin 535 

Antler  Peak,  features  of 20-23 

sections  at 21,  22 

view  of S2 

Apatite,  occurrence  of 402 

Araliaceai 744 

Aralia  angustiloba  Lx 745 

Araliii  digitata  Ward 748 

Aralia  macrophylla  Xewby 748 

Aralia  notata  Lx 745-747, 840 

Aralia  serrulata  n.  sp 747-748, 54J 

Aralia  sp 749 

Aralia  whitneyi  Ls 74S,53S 

Aralia  wrigbtii  n.  sp 744-745,  847 

Area  sp G38 

Archimedes  sp 492,  519-5!^0 

Arctostophylos  el]i;itica  n.sp 750-751,  874 

Arctostojibylus  uva-ursi  (L.)  Spreug 750 

Arionellus  (Bathyurus)  texanua  Shumard 460 

Arionellus  levis  n.sp 46'i-463,47'5 

Arionellus  sp.  undet 463,475 

Arionellus  tripunctatus  Whitfield 460,461 

Artocarpus  incisa  L 717 

Artocarpus  lessigiana  (Lx.)  Kn 717 

Artocarpus/  quercoides  u.  sp 716-718,554 

Aspleiiium  erosum  .' (Lx.)  Kn 668-669 

Asplenium  haguei  n.  sp 655,  754 

Asplenium  iddingsi  n.  sp 666-667,735.500 

Asplenium  magnum  n.sp 667,  068,  798 

Asplenium  remotidens  n.  sp 669,500 

Astarte  meeki  n.  sp 6^0,644 

Astarte  packardi 620 

Astarte  sp 6^0 

Athyris  angelica 505 

Athyris  asblaudensis  Herrick 502 

Athyris  claytoni 439 

Athyris  hirsuta 567 

Athyris  incrassata  White 488,  562,  563 

Athyris  incrassata  Hall  (?) 56t2-563 

Athyris  lamellosa  Meek 50I 

Athyris  lamellosa  L6veill6 561-56'-},  ^55 

Athyris  mira 570 

Athyris  occidentalis 505 

Athyris  occidentalis  var.  triplicata 505 

A  thyris  planosulcata  ( ? )  Hall  and  Whitfield . . .  489,  553, 554 

Athyris  roissyi 566-567 

Athyris  royssii  AValcott 560 

Athyris  vittata  var.  triplicata  n.  var 504-505,  580 

Atrypa  destjuamata  Walcott 502,503 

Atrypa  reticularis  L 481,502,  503.550 

883 


834 


INDEX. 


Page. 

Atrypa  missourieneis  Miller 481,  50!:i-504f  580 

Aulopora  geometrica  n.  gp 492,  308-500,  5S4 

Avalanclie  Peak,  dikes  and  rocks  of 305-30G 

Avicula  custa  Hall 617 

Avioula  liiigiiffiiorrais  Evans  and  Shumard 637 

Avicula  niucronata 610 

Avicula  nebrascena  Evans  and  Shumard 637 

Avicula  (Oxytoma)  nuicrouata  M.  and  H 616 

Avicula  (Oxytoma)  wyomingensis  n.  sp 61G-617 


Baculites  aspcr  Morton  (h 636 

Baldy  Mountain,  character  of  rocks  at 340,  344 

Banakite,  analyses  of 347 

character  and  occurrence  of 347-351 

photomicrograph  of 300 

Bannock  Peak,  features  of 31 

section  of 32 

view  of S3 

Barlow  Peak,  features  of 192-194 

fossils  of 193 

Baroda  wyomingensis  Meek 638 

Baronett  Peak,  view  of S04 

Basalt,  analysis  of 438 

character  of 239-240,241-242 

intermingling  of  rhyolite  and 430-432 

occurrence  of 24 1-242,  275-281 ,  302-304.  439 

photomicrographs  of SoO,  430 

Basaltpjrphyry,  occurrence  of 244 

Basaltic  andesite,  occurrence  of 296,302-304 

Bascom,  F.,  cited 63 

Bathyuriscus  Meek  (?) 466 

Bathyuriscus  sp.  undet 476 

Bathyurus  conicus  Billings 465 

Bear  Creek,  Montana,  analysis  of  rocks  from 352 

Beaverdam  Creek,  lavas  on 340,342,347,350 

Bechler  Canyon,  rhyolite  of    375-377 

Belemnites  densua  M.  antl  H 631-63''2 

Berr."  Creek,  section  of  rocks  on 153-154 

Betulaelliptica  Saj) 698 

Betula  iddingsi  n.  sp 69S-699,  S12 

Betulalutea  Michx 699 

Betula  parcedentata  Lx 698 

Betula  prisca  Ett 699 

Betula  stevensoni  Lx 698 

Betulacete,  descriptions  of  species  of 69$-699 

Big  Game  Ridge,  descriptive  geology  of 1G5-202 

features  of 188-191 

Bighorn  Pass,  features  of 24-27 

intrusive  sheet  at 69-72 

section  at 25-26 

Billingsella  Hall 450 

Billingsella  coloradocnsis  Shumard 450-431,  470 

Billingsella  pepina  Hall  and  Clarke 450 

Birch  Hills,  analysis  of  dacite  porphyry  of 163 

features  of 162-164 

Bobcat  Kidge,  rocks  of 180-181 

Bornemann,  J.  G.,  cited 442 

Brachiopoda,  descriptions  of  species  of. .  502-505,  609-610,  636 

Breccia,  acid,  occurrence  and  character  of 121-127, 

219-220.  237. 270-274, 281-296 

andesitic,  occurrence  of 4, 56, 91 

basic,  occurreuce  and  character  of 220-223, 

233-239,  275-281,  296-298 

Bridge  Creek,  rhyolite  on 386-387 

Briigger,  W.C.,  cited 246 


Page. 
Browne,  A.  J.  Jukes,  cited 40 

Bryozoa.  descriptions  of  species  of 516-576 

Buffalo  plateau,  geology  of 2U6-207 

Bnusen  Peak,  intrusive  rocks  of 86-88 

Bysmaiith,  definition  of 17-18 


Cache  Creek,  fossil  forest  on 760 

Caniaroplioria  ringens  Swallow 491, 337-338*  500 

Camarota-chia  flail 338 

Camarota'chia  camanfera  Winchell  (') 5J2 

Camaroto'chia  herrickana  n.  sp 339,  541. 542, 5yO 

Camarotfechiametallica  White 489,539,  340-341,  590 

Camarotcechia  orbicularis 543 

Camarotcechia  sappho  Hall 492,  34t*34!8 

Camarotttchia  sp 34ii-343)  590 

Cambrian  fossils,  descriptions  of 440-478 

lists  of 440-441 

plates  showing 46S-478 

Camptonectes  (Agasaiz)  Meek 613 

Camptonectes  beilistriatus  Meek 613-614,64:? 

Camptouectea  beilistriatus  var  distans  n.  var 614,  643 

Camptonectes    extenuatus    (M.  and  H.)   Hall  and 

Whitfield 613 

Camptonectes  extenuatus  (M.  and  H.)  Whitfield.  614,615,616 
Camptonectes    pertenuistriatus     Hall    and    Whit- 
field   614-613,616,6^ 

Camptonectes  platessiformis  White 613-616 

Capulus  paralius  Winchell 576 

Carboniferous  fossils,  table  showing  range  of 484-486 

Carboniferous  and  Devonian  fossils,  descriptions  of.  479-559 

plates  showing 680-598 

Cardium  pauperculum  Meek 638 

Cardium  shumardi  M.  and  H 621 

Cardium  subcurtum  Meek 638 

Carpites  pedunculatus  n.  sp 733, 846 

Carya  antiquorura  Newby 690 

Castanea  ungeri  Heer 701,703 

Castanea  pulchella  n.  sp 70S-704, 812,  S14 

Celastracea*,  descriptions  of  species  of 732-73 » 

Celastrus  culveri  n.sp 73'-2,  '^34 

Celaatrus  curvinervis  Ward 7J2 

Celastrus  ellipticus  n.sp 734,834 

Celastrus  injequalia  n.  sp 733,5^6" 

Celastrus  ovatus  Ward 699,732 

Cephalopoda,  descriptions  of  species  of 630-632,  636,  640 

Cerithium  (?)  sp 639 

Channel  Mountain,  features  of 196 

Chatani,  T.  M.,  analyses  of  rocks  by 135,352 

Chemical  analyses  of  rocks.     See  Analyses. 

Chicken  Ridge,  topographic  and  geologic  ieatures  of.  191-194 

Chonetes  illinoisensis 526 

Chonetes  logani  Norwood  and  Pratten 528 

Chonetes  loganensis  Hall  and  Whitfield 489, 

5ri3-5'.i7.  55'; 

Chonetes  ornatus  Shumard 3'-27-3'-28,  586 

Chrustachofl",  C.  von,  cited 418 

Cinnabar  Mountain,  section  of 53-54 

Cinnamomum  spectabile  Heer 7'^'i,  82S 

Cissus  haguei  n.  sp 741,  ^'4,? 

Cissus  parottiie folia  Lx 741 

Cladopora  labiosa 50 1 

Cladopora  plnguis 501 

Cladopora  sp 300-30I 

Cliothyris  King 366-367 

Cliothy ris  cras.sicardioalis  W  hite 562,  367-368,  59^ 


INDEX. 


885 


Page.    1 

Cliotliyria  craasicnrdinaUa  var  naua  u.  var 500,  ^i*''  , 

Cliotliyris  birHtitn 569  j 

Cliolli.vrta  obmnxinia 568 

Cliotl.yiis  roiasyi  Leveille 506  j 

Cliolhyrisroiasyl'Wnlcott 502..5«O-.'J»  I    ] 

Clisioptiyllum  teres  n.sp 514-515,  f'S-t 

Ctplenterata.  dest-riptions  of  species  of 50H-516  I 

Coloradc  formation,  fossiU  of Gu'i-6ii6 

d08cri])tions  ot  fosaila  of 6:i3 

CoiuiiiDar  Clitt,  Madison  Canyon  view  of . .     SGS 

Colinnuar  structure,  plate  showing -^36 

ConaiJt  Creek,  character  of  rhyolite  on 377-378 

rocks  of 161 

Conchita  rboniboidalis  Wilckcns 525 

Coniferiu  descriptions  of  species  of C70-683 

CoDocardiuiu  iiaiioU-onense  Winchell 571 

Conocardiuni  pukbellum  White  and 'WbitfieM 571- 

5»2,  5S1 

Conocardium  semipleniini 

Conoeardiuiii  trigonale  Hall 

Conocephalites  hamulus  Hall 

Couocephalltcs  wiscouensis  Hall 

Couocephalus  antiqnatus. 


571 

r.71 

4tl 

401 

456 

Corbula  subtrigonalis  M.  and  H W35 

Corbulua  subtrigonalis  var.  perundata 635 

Conmya  glabra  Agaasiz 628 

Cornace.'e 740 

Corn  us  acuminata  Newby "*9  | 

Corn  us  newberryi  Hollick 749 

Corn  us  ovalis  Ls 750 

Cornus  paniculata  L'Oer 730 

Cornus  wrightiin,  sp 749-750. 54/; 

Corylus  raacquarryi  (Forbes)  Beer 699,  S12 

Cottonwood  Creek,  Montana,  analysis  of  rock  from..         352 

Coulter  Creek,  rocks  of 179-180  : 

Coulter  Veak.  rocks  of 318-319  j 

Crags  (The)   features  of 3-5   , 

Cranilall  Basin,  acid  breccia  of 237  ' 

basalt  flows  of 239-240 

basic  breccia  of 238 

dissected  volcano  of 245-268  j 

estentof  erosion  in 232-233  ' 

intrusive  rocks  of 240-259  | 

lavatiowsof 238-239  j 

map  showing  dissected  volcano  of -216 

Craudall  volcano,  analyses  of  rocks  of 290-267 

Crania  levis  Keyes 520-5iJ  1 ,  5S6 

Crania  niodesta 520 

Cianiapermiana 520 

Crania  rowJeyi 520 

Credneria'  pachyphyllan.  sp 74!J,  54^ 

Credneriacere 742-743 

Crepicephalus  Owen 459-4t»0 

Crepicephalns  iowenais 459, 460 

Crepicephalus  (Loganellus)  raaculoaus 405 

Crepicephalus  (Loganellus)  montanensis 460 

Crepicephalus  onustis 400 

Crepicephalus  texanus  Sbumard 460,  460-461,  47S 

Crepicephalus  wisconensis 459,461 

Cretaceous  fossils,  occurrence  of 604-607 

description  of 632-640 

Crimson  Peak,  rocks  ot 158 

Cross,  Whitman,  cited 17 

Crowfoot  Ridge,  features  of 3,  5, 6.  27-30 

fossils  of 495-196 

Paleozoic  section  at 6-8. ,? 

Crustacea,  descriptions  of  species  of 576-578 


Page, 

Ciystala  in  rliyolile,  forma  of  growth  of 410-410 

CuVuUea  haguei  Meek 618,^44 

Cupreswintixylon  i-utroton  Felix 764 

Cyat  hophyllum  ca-.spitosum  Goldfnaa  ( f) 481, 500 

Cyperacitesgiganteus  n.  sp 684,  504 

Cyperacites  sp 684,  6S5,  Sor, 

Cyperaccir.  descriptions  of  species  of 684-085 

Cypricardia  batbimica  d'Orbigny 023-024 

Cypricardia  (  0  baguei  n.sp &'i3-G'24.,  Gt4 

Cypriua  cinnabarensis  n.  sp  — 6'21-ti'^t2,  r44 

Cyprina  (  0  iddingsi  n.  sp 6*-2S,  G44 

D. 

Dacite,  oc  :urrences  of 172-173, 288-290 

photomicriigrapLs  of 104,  ISO 

Dacite-porphyry,  analyses  of 05, 163 

character  of 64-69,84-85,86-88 

photomicrograph  of ('- 

Dakot  a  conglomerate,  occurrence  of 48,  49 

Dakota  formation,  fossils  of 604-605, 632 

Dakota  limestone,  occurrence  of 49 

Dana,  J.  D.,  cited 245,491 

Darwin,  Charles,  cited 82 

Daubree,  A.,  cited 418 

Derbyakeokuk  Hall  (?) 491,492,524-5*^5 

Devallia?  montana  n.sp 671-673,  793 

Devonian  fossils,  descriptions  of 496-507 

table  showing 483 

Devonian  and  Carboniferous  fossils,  descriptions  of.  479-599 

plates  showing uSO-oOS 

Dicellocephalua  latifrons  Sbumard 461-462 

Dicellomus  Hall 446 

Dicellomus  nana 440,465 

Dicellomus  nanus  M.  and  H 446,447 

Dicellon.us  politus 446,465 

Dielasma  burlingtonense  White 545 

Dielasma  forraosum  Hall 544 

Dielasma  rowleyi  Hall  and  Clarke 545 

Dielasma  Utah  Hall  and  Whitfield 489,  544-545, 550 

Dike  rocks,  characters  of 94-97, 128-133 

grades  of  cry stullization  of 107-108, 113-114 

variation  iu  mineral  composition  of 105-113 

Dikes,  occurrence  of 10,24,224-231 

features  of 224-231.240-259,304-321 

Diospyros  bracbysepala  Al.  Br 751 

Diospy ros  copeana  ix 75 1 

Diospyros  haguei  n.  sp 752,  753,540 

Diospyros  lamaren.sis  n.  sp 751-753,  SS0,S33 

Diospyros  obtusa  Ward 752 

Diospyros  stenosepala  Heer 663 

Diospyros  virginiana  L 752 

Diorite,  character  of 97-103 

mineral  composition  of 109-113 

occurrence  of 252-256 

photomicrographs  of 104, 2o0 

views  of  specimens  of 100 

Diorite-porpbyry,  occurrence  of 242-240,252-256 

photomicrographs  of 104,344 

view  of  specimen  of 100 

Dombeyopsis  iilatanoidea  Lx 661,  706 

Dome  (The),  features  of 12-13 

zone  of  contact  between  intruded  sheet  and  coun- 
try rocks  near. 68 

Donax  cuneata  Stanton 638 

Donas  ( .')  oblonga  Stanton 638 

Dosinia  jurasaica  Whitfield 622 


886 


INDEX. 


Page. 

Pryophyllum  aqnamanim  Ward 711 

Uryophyllum  longiiietiulatum  n.  sp 710*  SIG 

Dryophylluni  subtalcalum  Lx 711 

Dryopteris  weeilii  n.  sp 669-670,  SOJ 

Dryo])teri.-»  sautbolitbeusc  n.  sp 671*  S0:2 

E. 

Eagle  Peak,  view  of 296 

Eakins,  L.  G.,  chemical  analyses  of  rocks  made  by..  135 

260-261, 325, 329,  3-40,  347,  352 

Ebenacese 751 

Echo  Peak,  analysis  of  rocks  of G5 

banding  in  rocks  of 67-C8 

view  of 6S 

Ecbinoidea,  descriptions  of  species  of 609 

Ecliinodcrniata,  descriptions  of  species  of 515-516,608 

Edwards  and  Haime.  cited 498 

Electric  Peak,  analyses  of  intrusive  rocks  of 115-121 

chemical    correlation     of    rocks    of    Sepulchre 

Mountain  with  those  of 142-148 

comparison  of  rocks  from  Sepulchre  Mountain 

and 138-148 

diagram  showing  molecular  variation  of  rocks  at.  119 

diagram  showing  variation  in  silica  percentages 

of  rocks  at 117 

features  of 50-55,  89-92 

geologic  map  of OG 

grades  of  crystallization  of  rocks  of 107 

igneous  rocks  of 89-148 

intrusive  rocks  of 92-121 

location  and  altitude  of I 

mineral  and  chemical  composition  of  intrusive 

rocks  of 105-121 

notable  intrusive  sheet  at 82-84 

order  of  eruption  of  rocks  at 140 

porphyries  at 94-97 

quartz-mica-diorite-porphy ry  at 103-  ]  05 

sections  at 50-51.53-54 

stock  rocks  and  apophyses  at 97-103 

views  of -  90 

Elieodcndron  polymorphum  "Ward 734-735,  5<34 

Ellis  formation,  I'ussils  of 174, 176 

Ellis  sandstone,  fossils  of 197 

Eudothyra  haileyi 590 

Endothyra  bailey i  var  parva  n.  var 492,  507,  590 

Eudothyra  howmani 507 

Endothyra  lobata 507 

E(iuisitacea-,  descriptions  of  species  of 674-676 

Equisetum  canaliculatum  n.  ap 675,  G16,S03 

Equisetumdeciduum  n.sp G7O,S0-2 

Equisetum  haguei  n.  sp 674,  302 

Equisetum  hiemale 676 

Equisetum  lesquereuxii  Kn 675 

Equisetum  limosum  L 674,  675 

Equisetum  robnatum 676 

Ericacea? 750 

Eridopora  (?)  sp 517 

Etna  (Mount),  profile  of ^32 

Eumetria  altirostris  White 560 

Eumetria  vera 560 

Eumetria  verneuiliana  Hall 491,  493,  560-561 ,  5S7 

Eumetria  verneuiliana  Whitfield 560 

Eumicrotiscurta  (Hall)  ileek  and  Hayden 617 

Euomphalus  luxus  White 489,  573 

Euomphaliis  (StraparoUus)  ophirensis 489 

Euomphalus  (StraparoUus)  utahensis  Hall  and  Whit- 
field  489,573 


Fagaceae,  descriptions  of  species  of. , 

Fagus  antipofii  Abich 

Fagus  atlantica  Ung , 

Fagus  castanea?folia  tJng 

Fagus  dentata  Gopp , 

Fagus  feroniai  Ung 

Fagus  ferrugioea  Ait 


Page. 

700-702 

700 

701 

701 

700,701 

701 

700 

Fagus  undulata  n.  sp 700-703,  703.  SI ) 

Fails  River  Pasin,  basalt  in 435 

rhyoUte  in 377-379 

Fan  Creek,  rocks  on  and  near 43-44,45,46,47,48,  58 

sections  on  and  near 48, 58 

Fan  Pass,  rocks  of 49 

section  at 49 

Fan  (The),  features  of 45-50 

Favosites  sp 501,580 

Fawn  Creek,  rocks  on 43 

Fawn  Creek  Valley,  features  of 39-40 

section  in 38 

Fawn  Pass,  formations  exposed  near 42-43 

rocks  near 43 

Feldspar  raicrolitcs,  photomicrograph  showing 433 

Feldspar  needles,  photomicrograph  showing 414 

Fenestella  Lonsdale 518-519 

Filices,  descriptions  of  species  of 665-673 

Ficus  asiminje folia  Lx 713,  716 

Ficus  deformata  n.sp 712-713.5^5 

Ficus  densifolia  n.sp 714-715,  S1S,S20,S23 

Ficus  haguei  n.sp 715-716,5^0 

Ficus  shortensis?  Lx 714 

Ficus  sordida  Lx 714 

Ficus  sp 713,515 

Ficus  tilia-folia?  Al.  Br 716 

Ficus  ungeriLx 713,520 

Flat  Mountain,  rocks  and  fossils  of 196-197 

Flora,  fossil,  description  of 651-882 

plates  showing 704-8S2 

Forellen  Peak,  rocks  of 158-159 

Forests,  fossil 755-760 

Fort  Ellis,  Montana,  analysis  of  rocks  from 352 

Fraxinus  affinia  Newby 739 

Fraxinus  denticulata  Heer 66^,  798 

Fraxinus  heerii  Lx 753 

Fraxinus  wrightii  n.  sp 753,  8S0 

Friedel  and  Sarasin,  cited 418 

Gr. 

Gabbro,  occurrence  of 246-252 

photomicrograph  of 250 

Gabbro-porphyry,  occurrence  of 242, 246-252 

Gallatin  fault,  course  of 30 

Gallatin  Mountains,  descriptive  geology  of 1-59 

extrusive  rocks  west  and  southwest  of 137-138 

geologic  cross  sections  of 1-3 

intrusive  rocks  of 60-85 

map  of 56 

panoramic  view  of IS 

Gallatin  River,  geology  of  region  north  of 41-50 

laccolithic  mass  on 84-85 

section  near 58 

Gallatin  Valley,  features  of 27-30 

Gardiner  River,  rocks  near 45 

Gastropoda,  descriptions  of  species  of 505-  507, 

629-630;  632-633.  639 

Geikie,A.,andTealt,  J.J.  H.,cited 67 

(leonomites  schiraperi  Lx 658 


INDEX. 


887 


Page. 

Gerrilliiv  inoiitanaensia  Meek 617 

Gervillin  Kp 61 T 

Gibbon  liivt-r.  rliyolite  of 366-367 

Gilbert,  G.K.,  cited 17 

Gill.  A.C..ackiiowI*MlK»'nu*nt3  to 18^ 

Girty.  (i.  H.,  ncUnowltMlj^inents  to 441 

dt'scriptions  i»l'  Devonian  and  Cnrbonifcrows  fos- 
sils hy 479-509 

Glass,  character  of 40:i 

plobulitic 406-408 

raicrolitic 408-410 

rliy  clitic 406 

Glyptoatvobus  ungeri  Hear 681 

Gneiss,  ticcurrenceof 4,  Iti,  2(J 

Goniobasis  gracilcnta  Meek 632 

Goniobasis  ( .')  increbescens  n.  sp 633,  *>-i>' 

Goiiiobasis  {  0  pealei  n.  sp 63*2-63.3.  04S 

Grand  Canyon  of  the  Tellowstone,  rocks  of 389-390 

Granite,  view  of  specimen  of 100 

Granitic  aplite,  photoiuicro^^raphs  of 250 

Gravel  Peak,  features  of 188-190 

Gray  Peak,  rocks  of 42-43, 73-82 

section  near 46 

Grewiopsia  aldersoui  n.  sp 743-744 

Grewiopsis  idatanifolia  VTard 744 

Grewiopsis  populifolia  Ward 729 

Grizzly  Teak,  dikes  and  rocks  of 306-307,  308,  310 

Grypba*a  calceola  var.  nebrascensis  Meek  and  Hay- 
den  61'^,  64:? 

Gryphsea  dilatata 611 

Gryphit'a  plaiioconvexa  Whitfield 611,  (j'4^ 

Gryph;va  vesicularis Oil 

Glyptostrubus  curopa'ua  (Brongt.)  Heer 681 

Gynjiiogramnia  haydenii  Lx 657 

Gyrodes  depressi  Meek 639 

Gyrodes  petrosa 639 

Hague,  Arnold,  letter  of  transmittal  by xiii  ; 

cited 220,  331   ' 

Haguia,  description  of 42'.£   , 

Haguia  sphrerica,  n.sp , 44!d-443,  474 

Haldatdu  Lys,  C.N.  A.de,  cited 418  I 

Hall.  James 446  ! 

Hall  and  Whitfield,  cited 487.498,499,526  | 

Hemipronitescreuistriata 540  [ 

Herrick,  C.  L.,  cited 493  I 

Hicoria  antifiuorum  (Xewby)  Kn 690   , 

Hicoria  crescentia,u.  sp 690-69 1 ,  SOS 

Hicoria  culveri  n.sp G9t~G9*i,S06  I 

Hicoria  ovata  (Mill.)  Britten 692  ' 

Hillebrand,  W.  F.,  analyses  by 354  I 

Hinde,  G.  J. ,  ci ted 442 

Hornblende-mica-audesites,  occurrence  of 290-291 

Holasterella  wrighti  var.  americana  n.  var HOS*  599 

Holmes,  W.H.,  cited 14.31,221,357,651-652,756 

Homomya  galiatinensis  n.sp ^*ZS-G'2^^  G4G 

Hoodoo  Basin,  features  of 223 

view  of 233 

Hoodoo  Mountain,  dikes  of 224 

dike  rocks  of 348 

Honiblende-audcsite,  occurrence  of 4, 291 

Hornblende-andesite-porpbyrj-,  analyses  of 81 

occurrence  of 77-80 

Hornblende-mica-andesite-porpbyry,  analyses  of 61,81 

character  of GO-64.  7;i-77 

occurrence  of 256-258 


Page. 

Hornblende-pyroxone-andeBito,  occurrence  of 258-259, 

291-204.300-301 
Hornbleudepyroxeueandesitepori>byry,  occurrence 

of 80 

Hoyt  Peak,  dikes  and  rocks  of 306-307 

Huckleberry  Mountain,  dacito  of 172-173 

descriptive  geology  of 165-202 

detailed  geology  of 170-173 

rbyolito  of 172 

1 1  urricane  Me.sa,  di  Ues  of 225-229 

nature  of,  volcanic  rocks  of 340, 346 

view  of - 226 

Hurricane  Ridge,  view  of SS6 

Hustedia  triangularis  Miller 560 

Hyatt,  A.,  cited 602 

Hyolithes  primordialia 454,  466, 4r4 

Hyolithes  (Theca)  primordialis  Hall 454 


Iddiugs,  J,  P.,  cited 17,  89,  261,  292,  333,  360 

Iddings  and  Pentield,  cited 380 

Igneous  rocks  of  Absaroka  Range  and  Two  Ocean 

Plateau 269-325 

Ilex  undulata  Lx 658 

Indian  Creek,  intrusive  sheet  north  of 68 

section  at 21 

Indian  Creek  laccolith,  features  of 10, 13-16, 60-64 

mode  of  origin  of 9 

Index  Peak,  view  of 213 

Inoceramus  acuteplicattis  n,  sp 634-635,  637,  648,650 

Inoceramus  alt  us 635 

Inoceramus  flaccid ua  White 634 

Inoceramus  fragilis 635 

Inoceramu.s  umbonatus  Meek  and  Hay  den 634 

Inoceramus  undabundus  Meek  and  Hayden 634 

Intrusive  flows,  Crandall  Basin 240-259 

Intrusive  rocks,  analyses  of 426 

Iphidea  Billings 447 

Iphidea  bella 448 

Iphidea  ctelata 448 

Iphidea  labradorica 448 

Iphidea  ornatella 443 

Iphidea  paunula  White 448 

Iphidea  prospectensis 448 

Iphidea  sculptilis  Meek 447-448, 449, 46S 

Iphidea  sp.  undet 449, 463 

Iris  Falls,  rhj-olite  at 376 

lahawooa  Canyon,  analysis  of  rocks  from 329 

dike  rocks  of 349 

J. 

Joseph  Peak,  igneous  m  ass  of 73-82 

rocks  of 43, 44 

section  at 47 

Juratrias  fossils 197 

Judd,J.W.,citert 243,245 

Jukes-Browne,  A.  J.,  cited 40 

Juglandacea^,  descriptions  of  species  of 687-693 

Juglans  californica  Lx 6*i7 

Juglans  crescentia,  n.  sp 6S9-690,  SOS 

Juglana  denticulata  Heer 689 

Juglans  egregiaLx 688 

Juglans  laurifolia  n.sp 688-689,  S06 

Juglans  nigella  Ung 691 

■Tuglans  rugosa  Lx 687-688 

Juglans  schimperi  Lx 688-689 


888 


INDEX. 


Page. 

Jurassic  fossils,  occurrence  of 174,  1 76 

description  of 601-604,  608-632 

K. 

Kersantite,  analyses  of 70 

characters  of 69-72 

Kinderbook  fossils,  list  of 490 

Jiing,  Clarence,  cited 82 

KnowltoD,  F.  H.,  acknowlotlgments  to 183 

Kuch.R..  cited 409 

Ivuntze,  Otto,  cited 652 

Kutorginaniiniitissima  II.  &  W 447 

Kutorgina  sculptilis  Meek 447 

L. 

Laccolitb,  definition  of 17 

Lamar  Valley,  rocks  of 207-208 

Lamination  and  banding,  occurrence  of 424-425 

Lampropbyric  rocks,  occurrence  of 259 

Laiamie  tlora,  discussion  of 663-665 

table  sbowing  distribution  of 663 

LastreagoldianaLx 670 

Lanracea?,  descriptions  of  species  of 722-729 

Laurinoxylon  arouiaticura  Felix 767 

Laurinoxylonbrauneri  Kn 766 

Laurinoxylon  Icsquereuxiana  Ku 767 

Laurinoxylon  piilcbrum  n.  sp 765,  767, 575,  87S.  SSO 

Laurus  californica  Lx 724,  725 

Laurus  grandis  Lx 723,724,  7«5^A'i'C,  530 

Laurus  montana  n.  sp 724,  630 

Laurus  perdita  n.sp 723.  82S 

Laurus primizenja  (?)  Ung 722-723, 5^;J 

Laurus  princeps  Heer 725,  SSO 

Laurus  triseriata  Gasp 766-767 

Lava,  rbyolitic,  occurrence  of 4, 5 

Lava  flows,  Crandall  Basin 238-230 

Leguniinosa?.  description  of  species  of 729-730 

Leguminosites  cassioides  Lx 730 

Leguminoaites  lamareusis  n.sp 731,  SIS 

Leguminosites  lesquereuxianaKn 730,  SIS 

Leguminosites  proserpinaj  Heer 731 

Leptiena  rbomboidalis  Wilckons 488, 489, 492, 525 

LeptsnatenuistriataHall 525 

Lesquereux,  L.,  fossil  plants  determined  by 651 

Leucite-banakite,  analyses  of 347 

Limestone,  dikes  in 24 

Limacinnabarensis  n.  sp 612-613,  642 

Lindgren,  W.,  cited 353 

Liugula  brevirostris  M.  and  H 608 

Lingula  sp.  undet. 608 

Lingula  subspatulata  Hall  and  Meek 636 

Lingulepis  Hall 443-444 

Liorhyncbus  greenian\im  niricb 503 

Liorbyucbus  bagut'i  n.sp 543-544, 5.9t) 

Liorhyncbus  Kelloggi 544 

Liostracus  parvus  u.np 463-464,  475 

Liorhyncbus  (Pugnax?)  striatocostatum  M.  and  W.  544 

Lithoidal  rhyolite,  views  of 304 

Lithoiditt',  character  of 364-365 

Litbopbysfe,  characters  of 416-422 

diagrams  of ■^" 

views  of 364 

Lithostrotionsp 513-514 

Litseacnneata  u.  sp 726-727,  S24 

Litsea  weediana  Kn 659 


Page. 
Little  Quadrant  Mountain,  features  of 36-39 

sections  of  beds  at 36,  37,  38 

Little  Sunlight  Creek,  fossils  from 481 

Lower  Carboniferous  fossils,  table  showing  range  of.  484-486 

descriptions  of 507  -578 

Lower  Geyser  Basin,  rhyolite  of 369-372.374-375 

Loxonema  delicatum  n.  sp 506,  5S0 

Loxonema  tenuilineatum  Swallow 572 

Loxonema  ( ? )  sp 572, 5S0 

Lygodium  kaulfusii  Heer 672-673,500 

Lygodium  neuropteroides  Lx 672 

Lyosoma  powelli  White 630 

]vr. 

Mactra  arenaria  Meek  (?) 639 

Mactra    (Cymbopbora?)    warrenana    (M.   and    H.) 

Meek 639 

Mactra  (Trigonella?)  arenaria  Meek 610 

Mactra  warrenana  Meek  and  Hayden 639 

Madison  limestone,  fossils  of 487-488, 490, 491 

table  showing  zoological  groups  <  f 495 

Madison  Plateau,  rhyolite  of 367-369 

Madison  Range,  features  of  eastern  flank  of 57-59 

Madison  Kiver,  rhyolite  of 366-367 

Magnetite,  occurrence  of 400-401 

Magnolia  acuminata  L 721 

Magnolia  californica  (?)  Lx 718,  721 

Magnolia  culveri  n.sp 720-721, 5i?4 

Magnolia  foitida  Sarg 719 

Magnolia  grandifloraL 719 

Magnolia  inglefeldi  Heer 719, 720 

Magnolia  lanceolataLx 719 

Magnolia  micropbylla  n.  sp 720 

Magnolia  poUardi  n.sp 721, 50i 

Magnolia  spectabilis  n.sp 718-720,5-''6 

Magnoliacere,  descriptions  of  species  of 718-722 

Malopoenna  lamarensis  n.  sp 726,  Si?6".  55^ 

Malapoenna  weediana  ( ?)  Kn 639 

Mammuth  Hot  Springs,  character  of  rhyolites  at 357-359 

Martinia  rostrata  n.  sp ^  489,  553-554, 568, 504 

Mauna  Kea,  profile  of 2:)2 

Meek,  F.B.,  cited 482,487,489,494,611,619 

Melville,  W.  H.,  chemical  analyses  by 115,  261,  347. 354 

Meuophyllnm  ( ? )  excavatum 511-512,  ;'54 

Menopbyllum  tenuimarginatum 5U 

Merrill,  G.  P.  cited 351 

analyses  by 352 

Mesozuic  fossils,  descriptions  of 600-640 

plates  showing 641~6C0 

Meunier,  Stanislas,  cited 418 

Mica-dacite-porpbyry,  Bunsen  Peak,  analysis  of 87 

Miea-gneiss,  occurrence  of 4 

Michelinia  placenta  White 489,  510, 5S4 

Michelina  sp 489 

Microgranular  structure,  occurrence  of 422-423 

Micrograpbic  pbenocrysts,  photomicrographs  show- 
ing   414 

Micromita  Meek 447 

Middle  Creek,  dikes  on  and  near 224,312-314 

Minette,  analysis  of 70 

Mink  Creek,  rocks  and  fossils  of 199-200 

Modiola  subimbricata  Meek 617-618 

Modiola  (Vulsella)  subimbricata  Meek 617 

Montana,  character  of  absarokites  from 351-355 

Montana  formation.  fns.sils  of 606-6ii7 

description  of  fossils  of 636-640 


iNi)i:x. 


889 


Page 

Muuzoiitte,  pliotoinicrngrapha  of '2f>(i 

Mount  Doane,  amleait*'  of 315 

Muiiut  Kina  prolilo  ut '2si 

Mount  Kverts.  intruMvo  rocks  of 85-80 

ihyolilo  of 358 

Mount  Hancock,  tVatnresof UtO-191 

Mount  Holmis,  analysis  of  rocks  of 05 

featurts  of  by snialith  of 16-20,  64-09 

view  of  hysniatolitli  of ^S 

view  of  uiountaina  north  of 4 

zone  of  contact  between    iutriuled   sheet   and 

country  rock  lu-ar 08,  69 

Mount  Langfonl,  dike  at 312 

Mount  Norris,  fossil  (orust  on -*- TOU 

Mount  Norris  and  The  Thunderer,  view  of 2J? 

Mount  ScUurz.  rocks  of 310-318 

Mount  Stevenson,  rocks  of y  15-316 

Mount  Vesuvius,  profile  of '232 

Mugge,  O. ,  cited 390 

Musaceee,  descriptions  of  species  of 080-687 

Musophyllum  complicatum  Lx OSG-OSiyv^'j 

Myacites  (Pleuromya)  subconipressaMeek 626 

Myacites  subcompressus  (Meek)  White 626 

Myrica  bauksijefolia  Ung 693 

Myrica  bolanderi  ( ')  Ls. tt5S-659,  70r. 

Myrica  fallax  Lx 093 

Myrica  lamarensis  n  sp 693,  ^'f*5 

Myrica  polyraon)ha  ScUinip 692 

Myrica  scottii  Lx G9*Z-,S0S 

Myrica  torreyi  Lx 692 

Myrica  wardii  n.  sp 69*^-693,  SOS 

Myricacea?,  descriptions  of  species  of 69*-i-693 

Natica(?)  sp 630 

Naticopsis  (  ')  sp !i7'2y5Sl 

Katural  bridge.  Bridge  Creek,  rhj'olite  at 386-387 

views  of 3S6 

Neritina  nebraacensis  M.and  H 629-6JU 

Neritina  {  0  phaseolaris  AVhite 629 

Keritina  pisum  Meek G30 

Neritina  powelli  White 630 

Neritina  wyoraingensis  n.  sp «'i9-630,  C4.5 

Nucula  -sp OliS 

O. 

Obolella  Hall 446 

Obolella  chromatica 446 

Obolella  nana  M.  and  H 447 

Obolella  polita 446 

Obolus  Eichwald 443-444 

Obohis  (Lingulella)  desideratus  Walcott 445-446,  •J6\< 

Obolus  (Lingulella)  ferruginous 445 

Obolus  (Lingulella)  granvillensis 445 

Obolns  (Lingulella)  manticulus 445 

Obolus  (Lingulella)  perattenuatus 441 

Obolus  (Lingulella)  rotundatus 445 

Obolus  ( Lmgulepia)  acuminatus 443,  444 

Obolns  (Lingulepis)  acuminatus,  var.   meeki   Wal 

cott ^  44,  46H 

Obolus  ( Lingulepis)  pinniformis 443 

Obsidian  Cliff,  rhyolite  of 359-3tJ6 

views  of SCO 

OleaceiB ^ 7  53 

Onoclea  minima  u.  sp 656-657,  7.i-i 

Onoclea  sensibilis  fossilis  Newby 050,  006 


Page. 

Opbitic  ami  related  basalts,  occurrence  of 430-439 

Oppelia  (  0  ap 630-631 

Oppelia  subplicatclla  Vacek 031 

Orthis  coloradi>ensis  Sliuniard 45U 

Ortlns  crenistriata 524 

Ortbis  Kuok uk 524 

Orthis  niiclielina 521 

Ortbis  pi'pina  Hall 450 

Orthis  {.')  rt'iunicha 451-45*2,  470,472 

Orthis  (')  sandbergi 45*2-453, -/70 

Orthothetesina'qualisHall 489,  5*2*2-5*24,  oSO 

Orthothctcs  lutiatna 523.  r.SG 

Orthoihetes  sp 5*24 

Usniunda  atlinis  Lx 673,  SOO 

Osprey  Falls,  basalt  at 434 

Ostrca  auomioide!^  Meek 50,  633-634 

Ostrea  engelmanni  Meek 611 

Ostrea  patina OH 

Ostrea  pellucida  M .  and  H 037 

Ostrea  soleniscus  Meek 637 

Ostiea  sp .- 637 

Ostrea  strigilecula  White 61 0 

Outlet  Canyon,  topographic  and  geologic  features  of.   194-196 

view  of 204 

Owen.  D.  D.,  cited 459 

P. 

Pachyphyllura  bouchardi 499, 500 

Pachyphyllum  devoniense 499,500 

Pacliypbyllum  solitarium 499 

Pachyphyllum  sp 497-500 

Pachyphyllum  woodmani 498,  499 

Pacitic  Creek,  rocks  and  fossils  of 198-199 

Paleozoic  fossils,  descriptions  of 440-599 

Paliurus  colombi  Heer 060,  740,  S43 

Paliurus  minimus  n.  sp 659-660 

Paliurus  zizyphoides  Lx 660,  700 

Panther  Creek,  structure  of  mountains  south  of 9-JO 

Peale,  A.  C,  cited 439 

ibssils  collected  by GDI ,  602 

Pebble  Creek,  rocks  of 21I 

Pecten  bellistriata  Meek (J13 

Pelecypoda,  descriptions  of  species  of. . .  010,  632,  633-035,  637 

Pentacrinus  asteriscus  Meek  and  Hayden 60S 

Pentacrinus  whitei (jUS 

Perisphinctes  sp 631 

Perlite,  views  of  specimens  of 370 

Persea  pseudo-carolinenais  Lx 723,  7^25,  .SJO 

Perseoxylon  aromaticum  Felix 767 

Phenocrysts,  development  ol" 2G0-2C8 

Pholadomya  ina?(iuiplicata  n.  sp 6*25,  G4G 

Pholadomya  kingi  Meek 6*24-625,  6'4'j 

Pholadomya  multilineata  Gabb 625 

Pholadomya  nevadana  Gabb 624 

Pbragmites  alaskana  Heer 658 

Phragmites  falcata  n.  sp 65N,  706 

Pbragmites  ( ')  latissinia  u.  sp GS'-i.SOG 

Phyllites  crossifolia  n.  sp 753-754,  rS'^J  S4G 

Phyllites  osseus  Lx    754 

Pliylliles  sp ■^oo 

Pinna  kmgi  Meek 61S 

Pin  us  contorta  Dougl 680 

Pinus  contorta  murrayana 078 

Pinus  edulis  Engelm 680 

Pinus  Hexilis 678 

Pinus  gracilistrobua  n.  sp 611,676,500 


890 


INDEX. 


Page. 

Pinna  iddingsi  n.  sp GSO,S04 

Pinus  niacrolepia  n.ap G79,S00 

Piniis  piTniunayana  n.  sp G77-G7S.S04 

Pimm  scopulonim ^~^ 

Pinus  sp «r8-67» 

Pinus  Wardii  n.ap tt? »-680 

Pinyon  Peak,  features  of 184-188 

Pirsson,  L.  V.,  analyses  by ^54 

rited 241 

Pitcbstone  Plateau,  rhyolitc  of 379-381 

Pityosylon  aldersoni  n.  sp 763-764,  S52, 8G4,  SGfi,  873 

Pityoxylon  amelbystinuui  n.  sp.  ?  64-765,  S;*^,  S;<C.  SCS,  876 

Pityosylon  fallax  Ft-lix 764 

Placenticeras  placenta  (De  Kay)  Meek 640 

Plagiodase,  cbaracter  of  pbenocrysts  of 399 

Planera  longifolia  Lx 7I*-i 

Plants,  fossil,  descriptions  of 651-882 

localities  of 651-655 

plates  sbowiug 794-SS2 

Platanaceie,  descriptions  of  species  of 727-729 

Plataninium  iiaydeui Felix 767-769,  SSO 

Phitaninium  porosnm  Felix 760 

Platanrs  borealis  Casp 76.) 

Platanus  dubia  Lx 74j 

Platan  us  guillebnie  Gopp 727-728, 5J4 

Platanus  baydenii  Newby "06 

Platanus  klebsii  Casp 709 

Platanus  montana  n.ap 728-729,552 

Platanus  nobilia  Kewby 7-15 

Platanus  occidentalis  L 768 

Platanus  raynoldsii  Newby 72J 

Platycei-as  Conrad 574-576, 5Si 

Platyceras  cornuforme  Wincbell 574 

Platyceras  uebrascense  Meek 576 

Platyceras  primordialis  Hall  (  0 453, -i;4 

Platyceras  vomerium  WincbelJ 574 

Platycrinus  baydeni 515-516 

Platycrinus  symmetricus  Wacbsrauth  and  Springer.         488, 

515-516 

Platyatoma  minutura  n.sp 506-507,;'5y 

Pleuromya  newtoni  Wbittield 626 

Pleuromya  subcompressa  Meek 6^6-6^7,  646 

Pleuromya  webereusis  Meek 626 

Pleurotomaria  isaac.-si  Hall  and  Wbitfield  ( :')  .  480,  505,  5S0 

Pleurotoniaria  (?)  sp 506 

Pdpuloxy  Ion 769 

Populus  amblyrbyncba  Ward 694 

Populus  balsamoides  G fipp 696 

Populus  dapbnogenoides  Ward . : 696 

Populus  genatrixXewby 695 

Populus  glandulifera  Heer 694,  .W? 

Populus  greniopsis  Ward 696 

Populus  oxyrbyncba  Ward 694 

Populus  speciosa  Ward 694,805 

Populus(?)  vivaria  n.  sp 696-697,  S12 

Populus  xantbolitbenais  n.  sp 695-696 

Populus  zaddacbi  Heer 694 

Porifera,  descriptions  of  species  of 508 

Porpbyry,  occurrences  of in.  20,  94-97 

Productella  alifera  n.sp 492,530-531,  oS7 

Productella  arcuala  Hall 533 

Productella  concentrica  Hall 529,530 

Productella  eooperensis  Swallow 492,5*28-530,587 

Productella  pyxidea  Hall A 529,530 

Productella  shumardiana  Hall 529,530 

Trodnctus  flemingi  var.  burlingtoncnsis 535-536 

Productus  gallatineusis  n.sp 533-534,537,586,557 


Page. 

Productus  Isevicoata  Wbite 489, 534, 591 

Productus  Irevicostus  Wbite 534 

Productus  newbcrryi  Hall 531,  .'>32 

Productus  newbcrryi  var.  annoaus 536 

Productus  parviforniis  n.sp 488,533,536-537,586 

Productus  parvus  M.  and  W 488 

Productus  parvus  Wbite 488, 537 

Productus  papulata 532 

Productus  scabriculus  Martin 531-533,550 

Productus  semireticulatus  Martin  . .  489. 533,  535-536,  591 
Proetus  loganensis  Hall  and  Wbitfield..  489,  577-578, 5£>P 

Proetufl  peroccidens  Hall  and  Wbittield 489 

576-577,577,578,559 

Prospect  Peak,  analysis  of  basalt  from 438 

Protocaidia  sbumardi  M.  and  H 6^1 

Protozoa,  descriptions  of  species  of 507 

Pseudobrookite,  occurrence  of 401-402 

PseudomoRotis  curta  (Hall)  / 617 

Pseudomonotis  (Euiuicrotis)  curta  Hall 617 

Pteria  mucronata.M.and  H 616 

Pteria  (Osytoma)  munsteri  (Brown)  M.  and  H 616 

Ptf^ria  (Oxytoma)  nebrascana  (E.  and  S. )  Meek 637 

Pteris  erosa  Lx 668 

Ptcrosperniites  haguei  n.  sp 742,  838 

Ptiloporasp 517-518 

Ptychoparia  antiquata  Salter  sp 456-457,  458,  478 

Ptychoparia  (?)  diademata 460-461,  462,476 

Ptycboparia  eryon  Hall 458 

Ptycboparia  (Eulonia)  affinia  Walcott 457,  473 

Ptycboparia  Uanocnsis  Walcott  ( ?) i 458,  476 

Ptychoparia  (Loncbocepbalus)  liamulus  Owen, 461 

Ptycboparia  (Loncbocepbalus)  wisconsensis  Owen.     461- 

462 

Ptycboparia  penfiebli  n.  sp 456,  478 

I'tycboparia  sp.  undet 458,  476 

Ptycboparia  (  0  sp.  undet 458,  476 

Ptychoparia  striata 460 

Ptycboparia  teucer 458 

Ptycboparia  wisconsensis 476 

I'ugiunculus  primordialis  Hall 454 

Pumice,  occurrence  of 403-406 

Pyroxene,  cbaracter  of  pbenocrysts  of 399-400 

Pyroxene-andesite,  occurrence  of 294-295, 301-302 

photomicrographs  of ISO 

Py roxene-andesite-porpbyry,  Mount  Everts 85-86 

Pyrula  (?)  sp 639 

Q. 

Quadrant  formati4in,  comparison  of  sections  of 41 

Quadrant  Mountain,  rocks  of 33-35 

section  of 34-35 

Quartz,  characters  of  pbenocrysts  of 395-398 

Quartz-banakite,  analyses  of 347 

photomicrographs  of S50 

Quart z-mica-diorite,  occurrence  of 252-256 

Quartz-mica-diorite-porphyry,  characters  of 103-105 

Quartzite,  occ  urrence  of 7, 8, 33, 34, 47, 48 

Querciuium  knowltoni  Felix 772,773 

Quercin  um  lamarcnse  u.  sp.. -, 771-773,876,880,883 

Quercus  boweuiana  Lx 710 

Quercug  breweri  Lx 704 

Quercus  consimilis  ?  Newby 704,  314 

Quercua  culveri  n.  sp 708,  709, 8J4 

Quercus  drymc.ja  Ung 703 

Quercus  laurifoliu  Newby 708 

Quercus  ellisiana  Lx 659,  794 

Quercua  furcioervis  americaua  Kn 705, 816 


INDEX. 


891 


Page. 

Qiiercna  furc-inprvis  Rossm 705 

(^urrcns  gniulaiidica  Ucer 706 

(^utTciia  j;;rosHiiU*iitatii  ii.  sp 704,  S14 

Quercu8  lieaperia  n.  ap 709-7 1  <> 

Quert'iis  /  inflgiiifoliii  n.  sp 7D4-705,,S'i(; 

Quercus  olafpeni  Ileer 707 

QiierciiM  prinuiUca  Willd "09 

Querruss- 707, SIS 

Quercua  vibiirnitblia  Lx 700 

Qnorcua  weodii  n.  sp 705-706,  5n 

Quercus  yanceyi  n.  sp 707-708,  SJS 

Red  Creek,  rocks  od 175 

Red  Mountains,  rhyolite  of 381-382 

Reissanil  Stiibel.  cited 29J,400-41(t 

Eeticularia  cooiierensis  Swallow 489,  555-556*  568, 59.'5 

Reticularia  coopcrenais  var 556-557,  594 

Eeticularia  { ?)  poculiaris  Sliuniard 488,  557,  558,  595 

Reticularia  aetigera  Hall 556 

Retieularia  (?)  subrotundata  Hall 557-55S,  595 

Eetzia  (?)  circularis  Miller 560 

Retzia  ( ? )  plicata  Miller 560 

Retzia  popeana  Swallow 560 

Retzia  radialis  Walcott 560 

Retzia  vera  Hall 560 

Retzia  verueuili  Hall 5G0 

Ehaninacere,  deacriptiona  of  species  of 740 

Klianinacinium  radiatnm  Felix 769-77 1 ,  S70, S7S 

Rbamuusrectinervia  Heer 740 

Rliipidouu'Ua  michelina  Leveille S-Zl 

Rhus  bendirei  Lx 691 

Rhynclionella  camarif era  "Winchell 542 

Rbyncbonella  guatbopbora  Meek 609-6 1 0,  642 

Rbyncbonella  metallica  White 491,  540 

Rbyncbonella  myrina  Hall  and  Whitfield 600 

Rbyncbonella  pustulosa  (?) 489 

Rbyncbonella  pustuloaa  ( i)  Halland  Wbitfield..  489.  540,  590 

Rbyncbonella  ringeua  Swallow 537-  538 

Rbyncbonella  sappbo  Hall 541 

Rbyncbonella  (Stenocesma)  sappbo  Hall 541 

Rbyncbopborapuatulosa 540 

Rbyolitea,  analyses  of 420 

cbaraoter  and  occurrence  of 356-4:12 

cbaracters  of  groundmass  of 402-410 

intermingling  of  basalt  and 430--432 

microscopical  cbaracters  of 393-416 

occurrence  of 4, 5, 172 

variations  in  composition  of 427-429 

views  of 364 

Rbyolite  felsite,  analyses  of - 65 

Rbyolitic  glasses,  photomicrograpbs  of 406 

Roth,  J .,  cited 70, 146 

Rnssell,  I.  C,  cited 18 

S. 

Sabal  major  (?)Ung 658 

Saddle  Mountain,  rbyolite  of .-...  392 

Salicaceie,  descriptions  of  epecies  of 694-6^8 

Salix  angusta  Al.  Br 697 

Salix  lavateri  Heer 697 

Salix  varians  Heer 697.  siO 

Sanidine,  character  of  pbenocrysts  of 398-399 

Sapindua  affinis  New  by 736,737 

Sapindus  alatua  ?  Ward 7 .'57 

Sapindacea;,  descriptions  of  apeciea  of 736-739 


Page. 

Sapindus  grandifolioloides  n.  sp 7.1?*,.S'4f? 

Sapintlus  grandii'olioIuH  Ward 7.'l7,iVH 

Sapinclua  obtuaifoliua  Lx 7:'8 

Sapindus  ward ii  n.  sp 738,  739, 830,  SSS 

Scapbiocrhnis  sp 516 

Scaphites  cf.  ventricosus  M.  and  H 640 

Scapliites  veutricosii»  Meek  and  Hayden 636 

Schists,  occurrence  of 4, 11-12 

Schucbert,  Charles,  acknowledgments  to ^80 

Seminula  b nmilia  n.  sp 565-566,  568. 5US 

Seminula  immatura  n.sp 566,  59S 

Seminula  nindisonensia  n.  sp 41*2,  563-564,  5U3 

Seminula  madiaonensis  var.  perailla 564-565,  5uS 

Seminula  qiiadrata *4fl2 

Seminula  subtilita 4i  2  564,  .W5 

Seminula  wasatcheusis 5(55 

Sepulchre  Mountain,  analyses  of  rocks  of 261 

character  of  lava  at 340,341 

chemical  analyses  of  rocks  of i:  5-137 

chemical  correlation  of  rocks  of  Electric  Peak 

with  those  of 142-HS 

comparison  of  rocks  from  Electric  Peak  and 13-<-M8 

diagram  showing  mplecular  variations  of  rocka 

at 136 

dike  rocks  of 128-i:i3 

general  features  of 8J-92 

grades  of  crystallization  of  eruptive  rocks  of 131-133 

igneous  rocks  of 89-148 

mineral  an<l   chemical  composition  of  eruptive 

rocks  of 134-137 

order  of  eruption  of  rocks  at 140 

view  of 06 

volcanic  rocks  of 121-137 

Sequoia  couttsiaj  Heer 68 1 

Sequoia,  cones  of 683,  S02,  SOX 

Sequoia  langsdorfii?  (Brgt.)  Heer 657 

68'J-683,  794,304.994 

Sequoia  magnifica  n.  sp 76  l-76*-J,  S4S,  S50,  SCO,  SGI,  874 

Sequoia  reichenbachi  (Gein.)  Heer 657 

Sequoia  sempervirena 759 

Smithia  woodmani 498 

Smilacejp,  descriptiona  of  speciea  of 685-686 

Smilax  lamarensia  n.  sp 685-686,  SS2 

Smilax  iiser,do-8]>ina}  L 686 

Smilax  rotuudi folia  L 686 

Snake  River,  section  in  hills  near 156 

Snake  River  gorge,  geology  of 173-1 75 

coals  of 176 

Snake  River  fault,  features  of 197-198 

Snake  River  hot  springs,  features  of 177-^88 

view  of 175 

Snowy  Mountain,  section  at 206 

Snowy  Range,  sedimentary  rocks  of 205-206 

topography  and  geology  of  southern  end  of 20  1-244 

South  end  hills  of  Gallatin  Range,  features  of 10-11 

Siilenopleura  ( ? )  weedi 464-465, -175 

Soda  Butte  Creek,  rocks  of 210-21 1 

Soda  Butte  Valley,  geology  of 212-214 

sections  in 212,213-214 

Sparganiaceje,  descriptiona  of  species  of 683-6H4 

Sparganiura  stygium  Heer 683-681 

Specimen  Ridge,  fossil  forest  at 758 

lava  at 341 

Spherulitea  in  obsidian,  character  of 362-364 

figures  showing  sections  of 413 

forms  of 411-416 

views  of 370,  410,  414.  422 


892 


INDEX. 


Page. 

Shales,  occurrence  of 8, 15 

Shoshonite,  analyses  of 83,  340 

character  and  occurrence  of 339-347 

photomicrographs  of 344 

Silica  percentages,  rocks  of  Electric  Peak 116-118 

Slou;ih  Creek,  topography  ami  geoloj;y  of  valley  of.  208-210 

Spirifer  albapinensis ^89, 548, 594 

Spirifer  argentarius 550 

Spirifer  '   flicatus 548 

Spir'ft"  caraeratus 5'*0 

Spirifer  carter!  Hall 558 

Spirifer  centronata  H;h11  and  Whitfield 489,547 

Spirifer  centronatus  \Vinchell 488, 

489,  540,  347-549,  550,  552,  504 

Spirifer  centronatus  var.  semifurcatus 549-550,  594 

Spirifer  cuspidatus  Meek 559 

Spirifer  (Cyrtia)  bannibalensia  Swallow 558 

Spirifer  engelnianui  Meek 504,  5S0 

Spirifer  extenuatus ■^88 

Spirifer  forhesi 553 

Spirifer  hirtus  White  and  Whitfeld 555 

Spirifer  lauiellosus  L6veill6 561 

Spirifer  niarionensis  Shumard  (?) 551 

Spirifer  (Martinia)  glaber  Martin 554 

Spirifer  (Martinia)  peculiaris  White 488-557 

Spirifer  niesicostalis 5J9 

Spiiifer(.')  peculiaris  Shumard 557 

Spirifer  aetigera -189 

Spirifer  sp 55'^-553,;'.'>4 

Spirifer  sp 553 

Spirifer  striatus  White 488 

Spirfer  striatns  var.  madisonensis  u.  var.  488,  55 l-55'j.  694 

Spirifer  subattennatus  Hail 492,550 

Spirifer  (Syringothyria)  cuspidatus 59S 

Spirifera  albapinensis 489 

Spirifera  cooperensis  Swallow 555 

Spirifera  aetigera  K.  and  W 556 

Spirifera  subrotundata  Hall 557.558 

Spiriferinasolidorostris  Herrick 546,  ^.W 

Spiriferiua  solidorostris  White 545-547,5.99 

Spirigcra  euzona 565 

Spirigera  formosa 565 

Spirigera  monticola 488 

Spirigera  obraasiiua 488 

SphenopterisguyottiiLx 655 

Square  Butte,  Montana,  analyses  of  igneous  rocks 

from -■ 354 

Stanton,  T.  W.,  fossils  identified  by 193 

Stellaria  Creek,  rocks  on 45.46 

Stelzner,  A.,  cited 146 

Sterculiacete "42 

Stinking  water  Kiver,  dike  rocks  of 347,350 

nature  of  rocks  at 34(J,  345 

Stock  rocks,  characters  of 97-103 

StraparoUus  utahensis  Hall  and  Whitfield. .  489,  573-574, 

5S1 

Streptorliynchus  jequivalvis 522 

Streptorhynchus  equival vis 522 

Streptorhynchus  ina-qualis 522 

Streptorhynchus  inflatus 4S9 

Streptorbynchua  keokuk 524 

Strictoporella  (?) 518 

Strophomera  rhomboidalis  White 488, 489,  525 

Survey  Teak,  rocks  of 159-160 

section  at 1^0 

Sylvan  Paaa,  dikes  and  flows  near 304-314 

Syriugopora  aculeatau.  sp 509,  5S4 


Page. 

Syringopora  surcularia  n.  sp 510,  5S4 

Syringothyris  carteri  Hall 488, 492,  55N-559,  59S 

Syringothyria  cuspidatua  Walcott 559 

Syringothyris  extenuatus 488,559 

Syringothyria  ty pa  Winchell 558 

Tancredia  (?)  knowltoni  n. sp 6iil,6"44 

Tapea  wyomingensis  Meek 638 

Taxitis  olriki  Hess 6SO,  S04 

Terebratula  (Dielasma)  burlingtonensis 488 

Terebratula  gorby i  S.  A.  Miller 545 

Terebratula  marcyi  Shumard 561 

Terebratula  micbeliua 521 

Terebratula  Utah  Hall  and  Whitfield 489,544 

Tertiary  flora,  biological  consideration  of 773-783 

description  of  plants  of 665-791 

geological  consideration  of 783-981 

table  showing  distribution  of 749 

plates  showing  plants  of 79S-SS3 

Teton  Range,  crystalline  schists  of 152-157 

descriptive  geology  of  northern  end  of 149-164 

map  of  northern  end  of 150 

sedimentary  rocks  of 150 

1  topographic  features  of 151-152 

volcanic  rocks  of 157, 161-162 

I   Tetranthera  dealbata  R.  Br 726 

I   Tetranthera  sessiliflora  Lx 659 

I   Theca  gregaria 454 

I   Theca  primordialis  Hall 454 

Theca  (Piigiunculus)  gregaria  M.  and  H 454 

Thracia  (0  raontanaensis  (Meek)  ? 62fti,  C44 

Thracia  weedi  n.  sp 647,  64S 

Three  Kiver  Peak,  features  of 23-24 

rocks  of 16 

section  of 23 

view  of S4 

Thunderer  (The)  and  Mount  Xorris,  view  of 25? 

Tilia  populifolia  Lx 743 

Tiianiferous  iron  ore,  occurrence  of 400-401 

Tower  Falls,  basalt  at 434-435 

Trachytic  rbyolite,  occurrence  of 321-328 

Trapa  ?  microphylla  Lx 661,794 

Triaasic  fossils 197,600-601,608 

Trilobite  Point,  rocks  of 1 1-12 

zone  of  contact  between  intruded  sheet  and  coun- 
try rock  near 69 

Trigonia  americana  Meek 618-619,619 

Trigonia  costata 619 

Trigonia  elegantissima  Meek 619,  044 

Trigonia  montanaensis  Meek 619-640 

Tuff  (andesitic).  occurrence  of 4 

Tutf- breccia,  andesitic,  occurrence  of 56 

Turritellaap 630 

Two  Ocean  Pasa,  analysis  of  rocks  from 329 

character  of  lava  at 340.343 

chemical  composition  of  rocks  from 329,337 

Two  Ocean  Plateau,  rocks  of 258-:ii)0 

topography  and  geology  of 200-202 

Typhacea^,  descriptions  of  species  of 683 

XJ. 

Ulmacea*.  descriptions  of  species  of 711-712 

Ulmus,  fruits  of tVi^SlO 

rimus  minima?  Ward 711 

Ulmus  paeudo  fulva?  Lx 71  l,Si6 


INDEX. 


893 


Pago. 

U!mu»  rhaninifulia^  Ward 7  t''-i 

Vu'io  «p.  un<I(>t 6CI*<£ 

Upper  CteyatT  Uitsiii,  liiyulitoof 372-374 

Urticaceiu.  descriptions  of  wpeoiea  of 712-713 

V. 

VesuviuB  ( Slonnt).  profile  of 233 

Vildirnuni  roluudifoliiim  Lx 66!j,  7^*4,  W6 

Titaccir.  descriiitions  of  Bi»ecie8  of 741 

Volcanic  rocks  of  Absaroka  Kange  and  Two  Ocean 

Plateau 269-325 

Volselta  subimbricata  Whit© 617 

Walcott,  C.  D..  descriptions  of  Canibriau  fossils  by.  440-478 

TVall  Canyon,  fossils  from 480 

"Ward.  L.  F.,  paleobotanical  work  by 652 

"Waverly  group,  fossils  of 489,491 

Weed,  W.  H..  cited 53,  2ii6 

Weed  and  Pirsson,  cited 353 

White.  C.  A.,  cited 487,498,601 

Wbittield,  J.  E.,  chemical  analyses  made  by 61, 

65,  70,  81, 115, 135, 163,  325,  329,  340,  347 

citid 460 

Wildcat  Peak,  descriptive  geology  of 169-170 


Page. 

Williams,  G.H..  cited C3 

AViudy  Mountain,  dikrs  of 230 

■Wolverine  Creek,  rocks  of 181-182 

flora  of 183 

Woodwardia  areolata  (L.)  Moore GG6 

Woodvviirdia  crenata  Kn 656 

Woodwardia  latiloba  Lx 657,666 

A\'oiMh\  nrdia  jircareoliita  II.  sp <iC5-660,  TOS 

Wright.  Geo.  M.,  sections  made  by :i6,  38 

Y. 

Yancey's  Fossil  Forest,  description  of 756-757 

Yellowstone  Lake,  rhyolite  of  shores  of 382-385 

Yellowstone  lliver,  rocks  of  Grand  Canyon  of 380-390 

rhyolite  near 388-389 

Yogo  Peak,   Montana,   analyses  of  igneous  rocks 

from 354 

Z. 

Zircon,  occurrence  of 4U1 

Zizyphus  meekii  Lx 660 

Zizyphus  serrulata  Ward 740,  S42 

Zaconthoidea  spinosus 406 

Zaconthoidestypicalis 4C6 

Zacouthoides  sp.  undet .' 4ti5«4G6,  47<9 


ADVERTISEMENT. 

[Mouogiaiih  XXXII.] 


The  statute  approved  March  3,  1879,  establishing  the  Uiiiteil  States  Geological  Survey,  contains 
the  following  provisions: 

"The  puhlications  of  the  Geological  Survey  shall  consist  of  the  annual  report  of  operations,  geo- 
logical and  economic  inajis  illustrating  the  resources  and  elassitication  of  the  lauds,  and  leports  upon 
general  and  economic  geology  and  paleontology.  The  annual  report  of  ojierations  of  the  Geological 
Survey  shall  accom|)any  the  annual  report  of  the  Secretary  of  the  Interior.  All  special  memoirs  and 
reports  of  said  Survey  shall  be  issued  in  uniform  quarto  series  if  deemed  necessary  by  the  Director,  but 
otherwise  in  ordinary  octavos.  Three  thousand  copies  of  each  shall  be  puljlished  for  scientific  exchanges 
and  for  sale  at  the  price  of  publication ;  aiul  all  literary  and  cartographic  materials  received  iu  exchange 
shall  be  the  property  of  the  United  States  and  form  a  part  of  the  library  of  the  organization  :  And  the 
money  resulting  from  the  sale  of  such  publications  shall  he  covered  into  the  Treasury  of  the  United 
States." 

Except  in  those  cases  iu  which  an  extra  number  of  any  special  memoir  or  report  has  been  sup- 
plied to  the  Survey  by  special  resolution  of  Congress  or  has  been  ordered  hy  the  Secretary  of  the 
Interior,  this  oftice  has  no  copies  for  gratuitous  distribution. 

ANNUAL  REPORTS. 

I.  First  Annual  Report  of  the  United  States  Geological  Survey,  by  Clarence  King.  1880.  8"^.  79 
pp.     1  map. — A  jireliminary  report  describing  plan  of  organization  and  publications. 

II    Second  Annual  Report  of  the  United  States  Geological  Survey,  1880-'81,  by  J.  W.  Powell. 

1882.  S°.     Iv,  588  pji.     15L'  pi.     1  map. 

III.     Third  Annual  Report  of  the  United  States  Geological  Survey,  1881-'8M,  by  J.  W.  Powell. 

1883.  8*^.     xviii,  564  pp.     67  pi.  and  maps. 

•  IV.  Fourth  Annual  Report  of  the  United  States  Geological  Survey,  1882-'83,  by  J.  W.  Powell. 

1884.  8°.     xxxii,  473  pp.     85  pi.  and  mai>s. 

V.  Fifth  Annual   Report  of  the  United   States   Geological  Survey,  1883-'84,  by  J.  AV.  Powell. 

1885.  8°.     xxxvi,  4t)!l  pp.     58  )il.  and  maps. 

VI.  Sixth  Anuual  Report  of  the  United  States  Geological  Survey,  1884-85,  by  J.  W.  Powell. 
1885.     8*^.     xxix,  570  pp.     65  pi.  and  maps. 

VII.  Seventh  Annual  Report  of  the  United  States  Geological  Survey,  1885-'86,  by  J.  W.  Powell. 

1888.  S'^.     XX,  6.56  pp.     71  pi.  and  maps. 

VIII.  Eighth  Anuual  Report  of  the  United  States  Geological  Survey,  1886-87,  by  J.  W.  Powell. 

1889.  8"^.     2  jit.     xix,  474,  xii  p)).,  53  pi.  and  maps;  1  prel.  leaf,  475-1063  pp.,  54-76  pi.  and  maps. 

IX.  Ninth  Annual  Report  of  the  United  States  Geological  Survey,  1887-88,  by  J.  AV.  Powell. 

1889.  8"^.     xiii,  717  pp.     88  pi.  and  maps. 

X.  Tenth   Anuual    Report  of  the  United  States   Geological   Survey,  1888-'89,  bv  J.  AV.  Powell. 

1890.  8°.     2  pt.     XV,  774  pp.,  98  pi.  and  maps;  viii,  123  pp. 

XI.  Eleventh  Annual  Report  of  the  United  States  Geological  Survey,  1889-90,  by  J.  AV.  Powell. 

1891.  8>^.     2  pt.     XV,  757  jip.,  (Hi  pi.  and  maps;  ix,  351  pp.,  30  pi.  and  maps. 

XII.  Twelfth  Anuual  Ri-i)ort  of  the  United  States  Geological  Survey,  1890-'91,  by  J.  AV.  Powell. 
1891.     8°.    2  pt.,  xiii,  675  jip.,  53  pi.  and  maps ;  xviii,  576  pp.,  146  pi.  and  maps. 

XIII.  Thirteenth  Annual  Report  of  the  United  States  Geological  Survey,  1891-'92,  bv  .1.  AV. 
Powell.  1893.  8°.  3  lit.  vii,  240  pp.,  2  maps;  X,  372  pp.,  105  pi.  and  maps;  x'i,  486  jip.,  77 'pi.  and 
maps. 

XIV.  Fourteenth  Annual  Report  of  the  United  States  Geological  Survey,  1892-93,  bv  .1.  AA'. 
Powell.    1893.     8^.     2  j>t.     vi,  321  pp.,  1  ])1. ;  xx,  597  pp.,  74  pi.  and  maps. 

XA'.  Fifteenth  Annual  Report  of  the  United  States  Geological  Survey,  1893-'94,  by  J.  AA^  Powell. 
1895.     8^.     xiv,  755  pp.,  48  ])1.  and  nuips. 

XVI.  Sixteenth  Annual  Report  of  the  United  States  Geological  Survey,  1894-'95,  Charles  D. 
W^alcott,  Director.  1895.  (Part  I,  1896.)  «°.  4  pt.  xxii,  910  pp.,  117  pi.  and  maps;  six,  598  pp.,  43 
pi.  and  maps;  xv,  646  p|).,  23  pi. ;  xix,  735  pp.,  6  pi. 

XA^I.  Seventeenth  Aunual  Kepoit  of  the  United  States  Geological  Survey,  1895-'96,  Charles 
D.  AA'alcott,  Director.  18f6.  8^\  3  ]it.  in  4  vol.  xxii,  1076  pp.,  67  pi.  and  majis;  xxv,  8(34  pp.,  113  pi. 
and  maps;  xxiii,  542  pp.,  8  pi.  and  maps;  iii,  543-1058  pp.,  9-13  pi. 

XVIII.  Eighteenth  Aunual  Report  of  the  United  States  Geological  Survev,  1896-'97,  Charles  D. 
Walcott,  Director.     1897.    (Parts  II  and  III,  1898. )    8^.    5  pt.  in  6  vol.     1-440  pp.,  4  pi.  and  maps ;  i-v, 

I 


II  ADVERTISEMENT. 

1-653  pp.,  10.5  pi.  an  I  luaps;  i-v,  1-861  pp.,  118  pi.  ami  maps:  i-x,  1-756  pp.,  102  pi.  and  maps:  i-xii, 
1-642  pp.,  1  pi. ;  643-1400  pp. 

XIX.  NiueteentU  Annual  Report  of  the  United  States  Geological  Survey,  1897-'98,  Charles  U. 
Walcott,  Director.     1898.     8-.     6  pt.  iu  7  vol. 

MONOGRAPHS.     ' 

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II.  Tertiary  History  of  the  Grand  Canon  District,  with  Atlas,  by  Clarence  E.  Dutton,  Capt.,  U.  S.  A. 
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III.  Geology  of  the  Comstock  Lode  and  the  Washoe  District,  with  Atlas,  by  George  F.  Becker. 
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IV.  Comstock  Mining  and  Miners,  by  Eliot  Lord.     1883.     4^.     xiv,  451  pp.     3  pi.     Price  $1.50. 

V.  The  Cop])er-Beariug  Rocks  of  Lake  Superior,  by  Roland  Dner  Irving.  1883.  4^.  xvi,  464 
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VI.  Contributions  to  the  Knowledge  of  the  Older  Mesozoic  Flora  of  Virginia,  by  William  Morris 
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IX.  Brachlopoda  and  Lamellibranchiata  of  the  Raritan  Clays  and  Greensand  Mails  of  New 
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X.  Dinocerata.  A  Monograph  of  an  E.Ktinct  Order  of  Gigantic  Mammals,  by  Othniel  Charles 
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XI.  Geological  History  of  Lake  Lahontan,  a  (Juateruarj'  Lake  of  Northwestern  Nevada,  by 
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XII.  Geology  and  Mining  Industry  of  Leadville,  Color.ido,  with  Atlas,  by  Samuel  Franklin 
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XIII.  Geology  of  the  Quicksilver  Deposits  of  tlie  Pacific  Slope,  with  Atlas,  by  George  F.  Becker. 
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XV.  The  Potomac  or  Younger  Mesozoic  Flora,  by  William  Morris  Fontaine.  1889.  4"^.  xiv, 
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XVIII.  Gasteropoda  aud  Cephalopoda  of  the  Raritan  Clays  and  Greensand  Marls  of  New  Jersey, 
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Irving  .and  C.  R.  Van  Hise.     1892.     4^.     xix,  534  pp.     Price  $1.70. 

XX.  Geology  of  the  Eureka  District,  Nevada,  with  an  Atlas,  by  Arnold  Hague.  1892.  4".  xvii, 
419  pp.     8  pi.     Price  $5.25. 

XXI.  The  Tertiary  Rhynchophorous  Coleoptera  of  the  United  States,  by  Samuel  Hubbard  Soud- 
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XXII.  A  JIanual  of  Topographic  Methods,  by  Henry  Gannett,  Chief  Topographer.  1893.  i°. 
xiv.  300  pp.     18  pi.    Price  $1.00. 

XXIII.  Geology  of  the  Green  Mountains  in  Massachusetts,  by  Raphael  Pnmpelly,  T.  Nelson  Dale, 
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XXIV.  Mollnsca  and  Crustacea  of  the  Miocene  Formations  of  New  Jersey,  by  Robert  Parr  Whit- 
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XXV.  The  Glacial  Lake  Agassiz,  by  Warren  Upham.   1895.   4-.  xxiv,  658  pp.   38  pi.   Price  $1.70. 

XXVI.  Flora  of  the  Amboy  Clav.s,  by  John  Strong  Newberry;  a  P  sthumous  Work,  edited  by 
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XXVII.  Geology  of  the  Denver  Basin  in  Colorado,  by  Samuel  Franklin  Eunnons,  Whitman  Cross, 
aud  George  Homans  Eldridge.     1896.     4-.     5.56  pp.     31  pi.'     Price  $1.. 50. 

XXVIII.  The  Marquette  Iron-Bearing  District  of  Michigan,  with  Atlas,  by  C.  R.  Van  Hise  and 
W.  S.  Bayley,  iucluding  a  Chapter  on  the  Republic  Trough,  by  H.  L.  Smyth.  1895.  4^.  608  pp.  35 
pi.  and  atlas  of  39  sheets  folio.     Price  $5.75. 

XXIX.  Geology  of  Old  Hampshire  County,  Massachusetts,  comprising  Franklin,  Hampshire,  and 
Hampden  Counties,  by  Benjamin  Kendall  Emerson.     1898.     i"^'.     xxi,  790  pp.     35  pi.     Price  $1.90. 

XXX.  Fossil  Medusic,  by  Charles  Doolittle  Walcott.     1898.    4^'.     ix,201pp.     47  pi.     Price  $1.50. 

XXXI.  Geology  of  the  Aspen  Mining  District,  Colorado,  with  Atlas,  by  Josiah  Edward  Spurr. 
1898.     i°.    XXXV,  260  pp.     43  pi.  and  atlas  of  30  sheets  folio.     Price  $3.60. 

III  press: 

XXXII.  Geology  of  the  Yellowstone  National  Park,  Part  II,  Descriptive  Geology,  Petrography, 
aud  Paleontology,  by  Arnold  Hague,  J.  P.  Iddings,  W.  Harvey  Weed,  Charles  D.  Walcott,  G.  H.  Girty, 
T.  W.  Stanton,  and 'F.  H.  Kuowlton.     1899.     4-.     xvii,  893  pp.     121  pi.     Price . 

XXXV.  The  Later  Extinct  Floras  of  North  America,  by  John  Strong  Newberry;  edited  by 
Arthur  Hollick.     1898.     4'=.     xviii,  295  pp.     68  pi.     Price  $1.25. 


ADVEKTISEJIENT.  Ill 

In  prepaialhn: 

XXXIII.  (ieolofjy  of  tli«  NaiTiigJiiisctt  Basin,  1)y  N.  S.  Shaler,  .1.  H.  WooilwoitU.  ami  Aiij;ii8t  1'. 
Koei'ste. 

XXXIV.  Tlio  Glacial  (iravels  of  Maine  and  their  Associated  Deposits,  by  George  II.  Stone. 
XXX\I.  Till'  Crystal   Falls    Iron-Iioarinj;   District  of  Michij;an,   l)y  .1."  Morjrau  Clcuients  and 

Henry  I.loyil  Sniytli :  witli  a  C'liapirr  on  the  iStnrgeou  Kiver  Tongue,  liy  William  .Shirley  I'.ayloy. 
X.\.\\'1I.   I'lora  of  the  Lower  Coal  Measures  of  Jlissonri.  liv  David  White. 
XXXVIII.  The  Illinois  (ilacial  Lobe,  by  Frank  Leverett. 
— Flora  of  the  Laramie  and  Allied  Formations,  by  Frank  Hall  Knowlton. 

BULLI'yiTNS. 

1.  t)u  llyiiersthene-Amlesite  and  on  Trieliuie  Pyroxene  in  Augitic  Rocks,  by  WUirman  Cross, 
with  a  (ieological  Sketeli  of  Uulialo  I'eaks,  Colorado,  by  S.  V.  Emmons.  1«S3.  S  .  i2  pp.  2  pi, 
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2.  (iold  and  Silver  Conversion  Tables,  giving  the  Coining  Values  of  Troy  Ounces  of  Fine  Metal, 
etc.,  coni|iuted  by  Albert  Williams,  jr,      1><X3.     8-.      ^  W-     I'rice  5  cents. 

3.  On  the  Fossil  Faunas  of  the  Upper  Devonian,  along  the  Meridian  of  70^  30  ,  from  Tompkins 
County,  \.  v.,  to  Bradford  County,  I'a.,  by  Henry  S.  Williams.     18X4.     X'.     36  pp.     Price  5  cents. 

I.  On  Mesozoi(^  F'ossils,  by  Charles  A.  White.     1884.     8-.     36  pp.     il  pi.     Price  5  cents. 

a.  A  Dictionary  of  Altitudes  in  the  I'nited  States,  compiled  by  Henry  Gannett.  1884.  8-".  325 
pp.     Price  20  cents. 

6.  Elevations  in  the  Dominion  of  Canada,  by  . I.  AV.  Spencer.     1884.     8-.     43  pp.     Price  5  cents. 

7.  Mapoteca  (Jeologica  Anu'ricaiia.  A  Catalogue  of  (ieological  Maps  of  America  (Xorth  ami 
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1884.     8^.     184  i>p.     I'rice  lU  cents. 

8.  On  Secondary  Enlargements  of  Mineral  Fragments  in  Certain  Rocks,  by  R.  D.  Irviu"-  and 
O.K.  VanHise.      1884.     8^.     56  pp.      6  pi.      Price  10  cents. 

9.  A  Report  of  Work  done  in  the  Washington  Laboratory  during  the  Fiscal  Year  1883-84.  F.  W. 
Clarke,  Chief  Chemist;  T.  M.Chatard,  Assistant  Chennst.      1884.      8^.      40  pp.      Price  5  eeuts. 

10.  On  the  Cambrian  Faumis  of  North  America.  Preliminary  Studies,  by  Charles  Doolittle 
W'lcott.      18s4.      X-.      74  pp.      10  pi.      Price  5  cents. 

II.  On  the  (,)miternary  and  Recent  Mollnsca  of  the  Great  Basin;  with  Description  of  New 
Forms,  by  R.  Ellsworth  Call.  Introduced  bv  a  Sketch  of  the  Quaternary  Lakes  of  the  Great  Basin 
by  6.  K.  Gilbert.      1884.     S^'.     66  pp.     6  pi.      Price  5  cents. 

12.  A  Crystallographic  Study  of  the  Thinolite  of  Lake  Lahontan,  by  Edward  S.  Dana.  1884.  8^. 
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13.  Boundaries  of  the  United  States  and  of  the  Several  States  and  Territories,  with  a  Historical 
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14.  The  Electrical  and  Magnetic  Properties  of  the  Iron-Carburets,  by  Carl  Barns  and  Vincent 
Strouhal.     1885.     S"^.    238  pp.     Price  15  cents. 

15.  On  the  Mesozoic  and  Cenozoic  PakMuitology  of  California,  by  Charles  A.  White.  1885.  8'^. 
33  pp.     Price  5  cents. 

16.  <1n  the  Higher  I  )e\-oniau  Faunas  of  Ontario  County,  New  York,  by  John  M.  Clarke.  1885.  8^. 
86  pp.     3  pi.     Price  5  cents. 

17.  On  the  De\elopment  of  Crystallization  in  the  Igneous  Rocks  of  Washoe,  Nevada,  with  Notes 
on  the  Geology  of  the  District,  by  Arnold  Hague  and  Joseph  P.  Iddings.  1885.  8^.  44  pp.  Price  5 
cents. 

18.  On  Marine  Eocene,  Fresh-Water  Miocene,  and  other  Fossil  Mollnsca  of  Western  North 
America,  by  Charles  A.  White.     1885.    8"^.     26  pp.     3  pi.     Price  5  cents. 

19.  Noteson  the  Stratigra])hy  of  California,  by  (JeorgeF.  Becker.    1885.    8^'.    28  pp.    Price  5  cents. 

20.  Contributions  to  the  Mineralogv  of  the  Rockv  Mountains,  by  Whitman  Cross  and  W.  F.  Hille- 
brand.     1885.     8-.     114  i)p.     1  pi.     Price' 10  cents. 

21.  The  Lignites  of  the  (ireat  Sioux  Reservation;  a  Report  on  the  Region  between  the  Grand 
and  Morean  Rivers,  Dakota,  by  Bailey  Willis.     1885.     8"^.     16  pp.     5  pi.     Price  5  cents. 

22.  On  New  Cretaceou.s  Fossils  from  California,  by  Charles  A.  White.  1885.  8^.  25  i>p.  5  jd. 
Price  5  cents. 

23.  Observations  on  the  Junction  between  the  Eastern  Sandstone  and  the  Keweenaw  Series  on 
Keweenaw  Point,  Lake  Superior,  by  R.  D.  Irving  and  T.  C.  Chamberlin.  1885.  8^.  124  pp.  17  pi. 
Price  15  cents. 

24.  List  of  Marine  Mollnsca,  comprising  the  Quaternary  Fossils  and  Recent  Forms  from  American 
Localities  between  Cape  Hatteras  and  Cape  Roque,  incdudiug  the  Bermudas,  bv  William  Healev  Dall 
1885.     8°.     336  pp.     Price  25  cents. 

25.  The  Present  Technical  Condition  of  the  Steel  Indnstrv  of  the  United  States,  bv  Phineas 
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26.  Copper  Smelting,  by  Henry  M.  Howe.     1885.     8^.     107  pp.     Price  10  cents. 

27.  Report  of  Work  done  in  the  Division  of  Chemistry  and  Phvsics.  mainlvduring  the  Fiscal  Year 
1884-'85.     1886.     8^^.     80  pp.     Price  10  cents. 

28.  The  Gabbros  and  Associated  Hornlilende  Rocks  occurring  in  the  Neighborhood  of  Baltimore, 
Maryland,  by  (ieorge  Huntington  Williams.     1886.     8"^.     78  pp.     4  pi.    Price  10  cents. 

MON  XXXII 57 


IV  ADVERTISEMENT. 

2it.  On  tlie  Fresh-Water  In  vertebrates  of  the  Nortli  American  Jurassic,  hy  Charles  A.  White.  1886, 
H'^ .     41  pj).      4  1)1.     Price  .5  cents. 

30.  (Second  Coutributiou  to  tin-  Studies  on  the  Cambrian  Faunas  i>f  North  America,  by  Charles 
Dodlittle  Walcott.     188t).     8^.     369  i pp.      33  pi.     Price  25  cents. 

31.  Systematic  Keview  of  our  Present  Knowledf;e  of  Ft>s8il  Insects,  including  Myriapods  and 
Arachnids,  l>y  Samuel  Hubbard  Scudder.     1886.     8-.     128  ]ip.     Price  15  ceuts. 

32.  Lists  and  Analyses  of  the  iliueral  Springs  of  the  Fnited  States;  a  Prelinuuarv  Study,  by 
Albert  C.  Peale.     188(i.     8-.     235  pp.     Priie  20  cents. 

33.  Notes  on  the  Geology  of  Northern  Calilbrnia,l>y, I.  S.Diller.     1886.    8-.    23  pp.     Price  5  ceuts. 

34.  On  the  Relation  of  the  Laramie  Molluseau  Fauna  to  that  of  the  Succeeding  Fresh-Water  Eoceue 
and  Other  Groups,  by  Charles  A.  White.     1886.     8 -.     54  pp.     5  jd.     Price  10  ceuts. 

35.  Pliysieal  Properties  of  the  Irou-Carburcts,  by  Carl  Barus  and  A^iuceut  Strouhal.  1886.  8  . 
62  pp.     Price  10  cents. 

36.  Snbsidi-uceof  FineSolidParticlesiuLiiiuids,  by  CarlHarns.     1886.     8^.    .58pp.     PricelOcents. 

37.  Types  of  the  Laramie  Flora,  liy  Lester  F.  Ward.     1887.     8'^.     354  j)  p.     .57  pi.     Price  25  cents. 

38.  I'eridotiteofElliottCouuty,  Kentucky, by. I.  S.  Diller.     1887.     8-.    31pp.     Ipl.    Priceocents. 

39.  The  Fpper  Beaches  and  Deltas  of  the  Glacial  Lake  Agassiz,  1)V  Warren  rpluim.  1887.  8^. 
84  pp.     Ipl.     I'rice  10  cents. 

40.  Changes  in  Ki\er  Courses  iu  Washington  Territory  due  to  Glaciatiou,  by  Bailey  Willis.  1887. 
8^'.     10  PJ).     4  pi.      Price  5  cents. 

41.  ("In  the  Fossi',  Faunas  of  the  Upper  Devonian — the  Genesee  Section,  New  York,  by  Henry  S. 
Williams.     1887.     8^.     121pp.     4  ]il.     Price  15  cents. 

42.  Report  of  Work  done  iu  the  Division  of  Chemistryand  Physics,  uniinly  during  the  Fiscal  Year 
1885-86.     F.W.Clarke.  Chief  Chemi.st.     1887.     8-.     1.52  ]ip.     Ipl.     Price  15  ceuts. 

43.  Tertiary  and  Cretaceous  Strata  of  t\u'  Tuscaloosa,  Tombigl>ee,  and  Alal)ania  Rivers,  by  Eugeue 
A.  Sudth  au<l  Lawrence  C.  .Johnson.     1887.     8^.     189  pp.     21  pi.     Price  15  cents. 

44.  Bibliography  of  North  American  Geology  for  1886,  by  Nelson  H.  Dartou.  1887.  8^.  35  ])p. 
Price  5  cents. 

45.  The  Present  Coudition  of  Knowledge  of  the  (iecdogy  of  Texas,  by  Robert  T.  Hill.  1887.  8^. 
94  pp.     Price  10  ceuts. 

46.  Nature  and  Origin  of  Dejposits  of  Phosphate  of  Linu;,  by  R.  A.  F.  Penrose,  Jr.,  with  an  Intro- 
duction by  N.  S.  Shaler.     1888.     .s--.     143  p|i.     Price  15  cents. 

47.  .\ualyses  of  Waters  of  the  Yellowstone  National  Park,  with  an  Account  of  the  Methods  of 
Analysis  employed.  l>y  Frank  Austin  Gooch  aud  .James  Edward  Whitfield.  1888.  8"^.  84  pp.  Price 
10  ceuts. 

48.  On  the  Form  ,(nd  Position  of  tlie  Sea  Level,  by  Robert  Simpson  Woodward.  1888.  8-.  88 
pp.     Price  10  cents. 

49.  Latitudes  and  Longitudes  of  Certain  I'oints  iu  Mi.ssouri,  Kansas,  aud  New  Jlexico,  by  Robert 
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50.  Formulas  au<l  Tables  to  Facilitate  the  Construction  aud  Use  of  Maps,  by  Robert  Simpson 
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51.  Ou  luvertclprate  Fossils  from  the  Pacific  Coast,  by  Charles  Abiathar  White.  1889.  8^.  102 
pp.     14  pi.     Price  15  ceuts. 

52.  Subaiuial  Decay  of  Rocks  and  Origin  of  the  Rett  Color  of  Certain  Formatious,  liy  Israel 
Cook  Russell.     1889.     8^.'    65  pp.     5  pi.     PricelOcents. 

53.  The  Geology  of  Nautucket.  by  Nathaniel  .Southgate  Shaler.  1889.  8^^.  55  pp.  1(1  )d.  Price 
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54.  Ou  the  Thermo-Electric  Measurement  of  High  Temperatures,  by  Carl  Barns.  1889.  8"^. 
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55.  Report  of  Work  done  iu  the  Division  of  Chemistry  aud  Physics,  mainly  during  the  Fiscal 
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56.  Fossil  Wood  and  Lignite  of  the  I'otomac  Formation,  by  Frank  Hall  Knowltou.  1889.  8". 
72  pp.     7 1)1.     PricelOcents. 

57.  A  Geological  Reconuoissance  iu  Southwestern  Kansas,  by  Robert  Hay.  1890.  8^.  49  pp. 
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58.  The  Glacial  Boundary  in  Western  Pennsylvania,  Ohio,  Kentucky,  Indiana,  and  Illinois,  by 
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.59.  The  Ga1>bros  and  Associated  Rocks  in  Delaware,  by  Frederick  D.  Chester.  1890.  8"^.  45 
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60.  Report  of  Work  done  iu  the  Division  of  Chemistry  and  Physics,  nnxiuly  during  the  Fiscal 
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61.  Contributions  to  the  Mineralogy  of  the  Pacific  Coast,  by  William  Harlow  Melville  and  Wal- 
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62.  The  Greenstone  Schist  Areas  of  the  Mi-uominec  and  Maniuette  Regions  of  Michigan,  a  Con- 
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with  an  Introduction  by  Roland  Duer  Irying.     1890.     8^.     241  pp.     16  pi.     Price  30  ceuts. 

63.  A  Jiibliography  of  Paleozoic  Crnsta<'ea  from  1698  to  1889.  including  a  List  of  North  Amer- 
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64.  A  Report  of  Work  done  in  the  Divisiou  of  Chemistry  ami  Pliysics,  mainly  during  tlie  Fiscal 
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74.  The  Minerals  of  North  (_'arolina,  by  Frederick  Angiistns  Genth,  1891,  8^,  119  pp.  I'rice 
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76.  A  Dictionary  of  Altitndes  in  the  United  State.s  (Second  Edition K  compiled  by  Henry  Gannett, 
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78.  A  Report  of  Work  done  in  the  Division  of  Chemistry  and  Physics,  mainly  during  the  Fiscal 
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79.  A  Late  Volcanic  Eruption  in  Xorthern  California  ,'ind  its  Peculiar  Lava,  by  .J.  S.  Diller. 

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85.  Correlation  Papers — The  Newark  System,  by  Israel  Cook  Rnssell,  1892,  8-.  344  pp.  13  pi. 
Price  25  cents, 

8(5,  Correlation  Paper.s — Archean  and  Algonkian,  by  C,  R.  Van  Hise,  1892,  8  .  549  pp.  12  pi. 
Price  25  cents. 

87.  A  S.ynopsis  of  American  Fossil.  Brachiopoda,  including  Bibliography  and  Synonymy,  by 
Charles  Schiichert.     1897.     8.     464  pp.     Price  30  cents.  '  '  ■         ■     .■ 

88.  The  Cretaceons  Foramiiiifera  of  Nlmv  .Jersey,  by  Ruins  JIather  Kagg,  .Ir,  1898,  8°.  89  pp. 
6  pi.     Price  10  cents, 

89.  Some  Lava  Flows  of  the  Western  Slope  of  the  Sierra  Nevada,  Califoriria,  by  F,  Leslie 
Kansome.     1898.     S  ,     74  pp.     11  j)l.     Price  15  cents, 

90.  A  Report  of  Work  done  in  the  Division  of  Chemistry  and  Physics,  maiulv  during  the  Fiscal 
Year  1890-"91.     F,  W,  Clarke,  Chief  Chemist,     1892,     8^,     77  pp.     Price  10  cents. 

91.  Record  of  North  American  Geology  for  1890,  by  Nelson  Horatio  Darton,  1891.  8^,  88  pp. 
Price  10  cents, 

92.  The  Compressibility  of  Liquids,  by  Carl  Barns.     1892,     8'=,     96  jip.     29  pi.     Price  10  cents. 

93.  Some  Insects  of  Special  Interest  from  Florissant,  Colorado,  and  Other  Points  in  the  Tertiaries 
of  Colorado  and  Utah,  by  Samuel  Hubbard  Sendder.     1892,     8"^.     35  iiji.     3  jil.     Price  5  cents. 

94.  The  Mechaui.sm  of  Solid  Viscosity,  by  Carl  Barns.      1892.     8^-.     138  pji.     Price  15  cents. 

95.  Earthquakes  in  California  in  1890  anil  1891.  by  ICdward  Singleton  Holilen.  1892.  8^.  31pp. 
Price  5  cents. 

9().  The  Volume  Therniodynaniics  of  Liquids,  by  Carl  Barns.     1892.     8-.     100  p)i.     Price  10  cents, 

97.  The  Mesozoic  Echinodermata  of  the  United  States,  by  W,B,  Clark,  1893,  ^'-.  207  pp.  50  pi. 
Price  20  cents. 

98.  Flora  of  the  Outlying  Carboniferous  Basins  of  Southwestern  Missouri,  by  Da^dd  White. 
1893.     8^,     139  pp.     5  pi.     Price  15  cents, 

99.  Record  of  North  American  Geology  for  1891,  by  Nelson  Horatio  Daiton.  1892.  8'-\  73  jip. 
Price  10  cents. 

100.  Bibliography  and  Index  of  the  Publications  of  the  U.  S.  Geological  Survey,  1879-1892,  by 
Philip  Creveling  Warinan.     1893.     8°.     495  pp.     Price  25  cents. 

101.  Insect  Fauna  of  the  Rhode  Island  Coal  Field,  by  Samuel  Hubbard  Sendder.  1893.  8*^. 
27  pp.     2  pi.     Price  5  cents. 

102.  A  Catalogue  and  Bibliography  of  North  American  Mesozoic  Invertelirata,  by  Cornelius 
Breckinridge  Boyle,     1892,     8-,     315  ]ip,  '  Price  25  cents. 


VI  ADVERTISEMENT. 

103.  High  Temperatuif  AVovk  in  I-jin'ous  Fusion  ;iu(l  I'.lmllition,  cliiefiv  iu  Relation  to  Pressure, 
by  Carl  Barns.     1S93.     8S     57  ])p.     9  pL     Price  10  cents. 

101.  tilaeiation  of  the  Vellowstone  Valley  uortli  of  the  Park,  liy  Walter  Harrey  Weed.  1893.  8^. 
41  pp.     4  ]il.     Price  5  cents. 

105.  The  Larauiie  and  the  dverlyinn  Livingstone^  Fonuatlou  iu  Montana,  by  Walter  Harvey 
Weed,  with  Report  ou  Flora,  by  Frauli  Hall  Kuowlton.     1893.     8-.     68  pp.     t>  jil.     Price  10  cents. 

10().  The  Colorado  Formation  and  its  Invertebrate  Fauna,  by']'.  \V.  Stanton.  1893.  8-.  288 
)ip.     45  pi.     Price  20  cents. 

107.  Tlie  Trap  Dikes  of  the  Lalce  Cluimplaiu  Region,  by  .Tames  Furman  Kemp  and  Vernon 
Freeman  Marster.s.     1893.     8.     62  pp.     4  pi.     Price  10  cents. 

108.  A  Geological  Kecounoissance  in  Central  Washington,  by  Israel  Cook  Russell.  1893.  8-^. 
108  pp.     12  ]d.     Price  15  cents. 

109.  The  Krujitive  an<l  Sedimentary  Rocks  on  Pigeon  Point,  Miunesota,  and  their  Contact  Phe- 
nomena, by  William  Sliirley  Bayley.     1893.     8'^.     121pp.     1()  x)l.     Pi'ice  15  cents. 

110.  The  Paleozoic  Section  in  the  Vicinity  of  Three  Forks,  Montana,  by  Albert  Charles  Peale. 
893.     8^'.     56  pp.     6  pi.     Price  10  cents. 

111.  (ieology  of  the  Hig  Stone  (Jap  Coal  Fields  of  A'irninia  and  Kentucky,  by  Marins  R.  Camp- 
bell.    1893.     8-.    'l06pp.     6'pl.     Price  15  cents.  '   ' 

112.  Earth(|uakes  in  California  iu  1892,  l)y  Charles  D.  Perrine.     1893.    8^.    57i)p.    Price  10  cents. 

113.  A  Report  of  Work  <lonc  in  tlie  Diyision  of  Chemistry  during  the  Fiscal  Years  1891-92  and 
1892-93.     F.  W.  Clarke,  Chief  Chemist.     1893.     8-,     115  pp.     Price  1.5  cents. 

114.  Eartluinakes  in  Cililbrnia  in  1893.  by  Charles  D.  Perrine.    1894.    S-".    23  pp.    Price  5  cents. 

115.  A  (ieographic  Dictionary  of  Rhode  Island,  by  Henry  Gannett.  1894.  S°.  31  pp.  Price 
5  <'ents. 

116.  A  Geographic  Dictionary  of  Massachusetts,  by  Henry  (iannett.  1894.  8"^.  126  pp.  Price 
15  cents. 

117.  A  Geographic  Dictionary  of  Connecticut,  by  Henry  (Jannett.  1894.  8-.  67  pp.  Price  10 
cents. 

118.  A  (ieograjihie  Dictionary  of  Ne\y  .Jersey,  by  Henry  Gannett.  1894.  8^.  131pp.  Price  15 
cents. 

119.  A  Geological  Keconmii.ss^ince  in  Xorfliwest  Wyoming,  by  George  Homaus  Eldridge.  1894. 
8^.     72  pp.     Price  10  cents. 

120.  The  Devonian  System  of  Eastern  Pennyshania  and  New  York,  by  Charles  S.  Prosser.  1894. 
8^.     81pp.     2  pi.     Price  10  cents. 

121.  A  Bibliography  of  North  American  Paleontology,  by  Charles  Rollin  Keyes.  1894.  8-.  251 
pp.     Price  20  cents. 

122.  Results  of  Primary  Triangulatiou,  by  Henry  Gannett.  1894.  8  .  412  pp.  17  pi.  Price 
25  cents. 

123.  A  Dictionary  of  Geographic  Positions,  by  Henry  Gannett.  1895.  8'-.  183  pp.  1  pi.  Price 
15  cents. 

124.  Revision  of  North  American  Fossil  Cockroaches,  by  Samuel  Hubb:ird  Scndder.  1895.  8^. 
176  pp.     12  pi.     Price  15  cents. 

125.  The  Constitution  of  the  Silicates,  by  Frank  Wigglesworth  Clarke.  1895.  8-'.  109  pp. 
Price  15  cents. 

126.  A  Mineralogical  Lexicon  of  Franklin,  Hampshire,  and  Hampden  counties,  Massachnsetts, 
by  Benjamin  Kendall  l^nierson.     1895.     S^.     180  pp.     I  pi.     Price  15  cents. 

127.  Catalogue  and  Index  of  Contributions  to  North  American  Geology,  1732-1891,  by  Nelson 
Horatio  Darton.     1896.     8-.     1045  pp.     Price  60  cents. 

128.  The  Bear  River  I'ormatiou  and  its  Characteristic  Fauna,  by  Charles  A.  White.  1895.  8°. 
108  pj).     11  pi.     Price  15  cents. 

129.  Earthquakes  iu  California  in  1894,  by  Charles  D.  Perrine.    1895.     8^.     25  pp.     Price  5  cents. 

130.  Bibliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  1892  anil  1893".  by  Fred  Boughton  Weeks.     1896.     8-.     210  pp.     Price  20  cents. 

131.  Report  of  Progress  of  the  Division  of  Hydrography  for  the  Calendar  Years  1893  and  1894, 
by  Frederick  Haynes  Newell,  To]iographer  in  Charge.     1895.     8-.     126  p]>.     Price  15  cents. 

132.  The  Disseminated  Lead  Ores  of  Southeastern  Missouri,  by  Arthur  Winslow.  1896.  8°. 
31  pp.     Price  5  cents. 

133.  Contributions  to  the  Cretaceous  Paleontologv  of  the  Pacific  Coast:  The  F^auna  of  the 
Knoxville  Beds,  by  T.  W.  Stanton.     1895.     8^.     132  pp.     20  pi.     Price  15  cents. 

134.  The  Cambrian  Rocks  of  Pennsylvania,  by  Charles  Doolittle  Walcott.  1896.  8".  43  pp. 
15  pi.     Price  5  cents.  ' 

135.  Bibliography  and  In<lex  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Year  1X94,  by  F.  B.  Weeks.     1896.     8.     141pp.     Price  15  cents. 

136.  Volcanic  Rocks  of  South  Mountain,  Pennsylvania,  by  Florence  Basconi.  1896.  8-.  124  pp. 
28  pi.     Price  15  cents. 

137.  The  Geology  of  the  F'ort  Riley  Military  Reservation  and  Vicinity,  Kansas,  by  Robert  Hay. 
1896.     8'-.     35  pp.     8  pi.     Price  5  cents. 

138.  Artesian-Well  Prospects  in  the  Atlantic  Coastal  Plain  Region,  by  N.  H.  Darton.  1896.  8*^. 
228  pp.     19  pi.     Price  20  cents. 

139.  Geology  of  the  Castle  Mountain  Mining  District,  Montana,  by  W.  H.  Weed  and  L.  V.  Pirs- 
sou.     1896.     8-.     164  pp.     17  pi.     Price  15  cents. 

140.  Report  of  Progress  of  the  Divisicm  of  Hydrogr.aphy  for  the  Calendar  Year  1895,  by  Frederick 
Haynes  Newell,  Hydrographer  in  Charge,     1896.     8^.     3.56  pp.     Price  25  cents. 


ADVKKTISKMENT.  VII 

111.  The  Kocoiie  Deposits  of  the  Middle  Atlantic  Slope  iu  Delawair,  Marvland,  and  Virginia, 
by  William  l!iillo(d<  Clark.     18!l(i.     S.     167  pp.     40  pi.     Trice  l.">  cents, 

M'J.  A  liricl'  ('(intriliiition  to  the  tieoloyy  and  Paleontiilogy  of  Nortliwcsterii  l.ciiiisiaii.i.  liy 
T.  Wayland  Van};han.      IMlKi.     S-.     lio  pp.     1  pi.     Trice  lO  cents. 

lis.  \  Hililiography  of  Clays  .-ind  the  Ceramic  Arts,  l>y  .lnhn  ('.  T.raiiiur.  ISiM!,  S  .  Ill  pji. 
Price  1.5  cents. 

144.  'I'ho  Moraines  of  the  Mi.ssonri  Coloau  ami  their  .Attendant  lieposit.s,  liv  .lames  Kdwanl  Todd. 
1890.     8^.     71  p]).     -Jl  ]\\.     Trice  1(1  cents. 

14.").  The  Totomar  Torniation  iu  \'ir};inia,  liy  \V.  M.  Fontaine.  1896.  8  .  149  pp.  1'  pi.  Trice 
l.T  cents. 

146.  Hibliojjrapliy  and  Index  of  Nortli  American  (ieology,  Paleontolosv,  Petrology,  and  Miuer- 
alogy  lor  tlie  Year  181C),  by  K.  li.  Weeks.     1896.     8.     130  jij).     Price  1.5  cents'. 

147.  ICartlninakes  iu  California  in  189.j,  by  Charles  1).  Perriue,  A.ssistant  Astronomer  in  Charge 
of  Karth(|uako  I  Ibservations  at  tlie  Lick  Dbservatory.     1896.     8  .     23  p]).     Trice  5  cents. 

1 18.  Aualvscsof  Kocks.  with  a  Chapter  on  Anaivtical  Jlethods,  Laboratory  of  the  United  .States 
Geological  .'Guryev,  1880  to  1896,  by  F.  W.  Clarke  and  W.  F.  Hillebrand.  1897!  8-.  306  pp.  Trice 
20  cents. 

149.  Ulbliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Year  1.^96.  by  Fred  Houghton  Weeks.     1.^97.     8^.     152  iip.     Price  15  lents.  ' 

1.50.  Tlie  Fducational  Series  of  Koclc  .Specimens  collected  and  distributed  by  the  United  .States 
Geidogical  Siiryey,  by  .loseph  Silas  Diller.     180!S.     8-.     398  pp.     47  pi.     Price  25  cents. 

151.  '['he  Lower  Cretaceous  Gryi>haas  of  the  Texas  Region,  by  R.  T.  Hill  and  T.  Wavlaiid 
Vaughau.     1898.     8  .     139  jip.     25  pi.     Price  15  cents. 

152.  A  Catalogue  of  tlie  Cretaceous  and  Tertiary  Plants  of  Xortli  America,  by  F.  H.  Knowlton. 
1898.     8'^.     247  pp.     Trice  20  cents. 

153.  A  Bibliographic  Index  ol  North  American  Carboniferous  Invertebrates,  by  Stuart  Weller. 
1898.     S\     6.53  pp.     Trice  35  cents. 

1.54.  A  Gazetteer  of  Kansas,  by  Henry  Gannett.     1898.     8-^.     246  pp.     6  pi.     Price  20  cents. 

1.55.  Eartlii|uakes  in  California  in  1896  and  1897,  by  Charles  1).  Terrine,  Assistant  Astronomer 
in  Charge  of  Earthcjuake  Observations  at  th<' Lick  Obseryatory.     18118.     8-.     47  pp.     Trice  5  ceuts. 

15(5.  Bibliogra]iliy  and  Index  of  North  American  (ieology,  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Y'ear  1897,  by  Fred  Houghton  Weeks.     1898.     8"-.     130  PI).     Trice  15  cents. 
/«  preparation: 

1.57.  The  Gneisses,  Gabbro-Sehists,  an<l  Associated  Kocks  of  .Southeastern  Minnesota,  by  C.  W. 
Hall. 

158.  The  Moraines  oi'  South  Hakota  and  their  Attendant  Deposits,  by  J.  E.  Todd. 

1.59.  The  Geology  of  Eastern  Berkshire  (ouuty,  Massachusetts,  by  B.  K.  Emerson. 

160.  A  iJictionary  of  Altitudes  in  the  United  States  (Third  Edition),  compiled  by  Henry 
Gannett. 

WATER-SUPPLY  AND  IRRIGATION  PATERS. 

By  act  of  Congress  approved  June  11,  1896,  the  following  proyisiou  was  made : 
"  I'roridcd,  That  hereafter  the  reports  of  the  Geolo'ical  Survej-  iu  relation  to  the  gauging  of 
streams  and  to  the  methods  of  utilizing  the  water  resources  may  be  prin  ed  in  octavo  form,  not  to 
exceed  one  hundred  pa.'es  in  length  and  live  thousand  copies  in  number;  one  thousand  copies  of  ^yIlich 
shall  be  for  the  otticial  use  of  the  (Jeological  Survey,  one  thousand  live  hundred  copies  shall  be  deliv- 
ered to  the  Senate,  and  two  thousand  five  hundred  copies  shall  be  delivered  to  the  House  of  Repre- 
seutatives.  ibr  distril>ution.' 

Under  this  law  the  following  ])apers  have  been  issued  : 

1.  Pumping  Water  lor  Irrigation,  by  Hcrl)ert  JI.  ''  ilson.     1896.     8-.     57  pp.     9  pi. 

2.  Irrigation  near  Thceuix,  Arizona,  by  Arthur  T.  Davis.     1897.     8^.     97  p]i.     31  pi. 

3.  Sewage  Irrigation,  by  George  W.  Rafter.     1.^97.     8.     100  jip.     4  ]il. 

4.  A  Recimnoissance  in  southeastern  AVashington,  by  Israel  Cook  Russell.    1897.    8  . 

5.  Irrigation  Tractiei- on  I  he  Great  Plains,  by  Elias  Brans(U»  Cowgill.     1897.     S^. 

6.  Underground  Waters  of  Southwestern  Kansas,  by  Er.-ismus  Ha  worth.    1897.    S-. 

7.  Seepage  Waters  of  Northern  Utah,  by  Samuel  Fortier.     1897.     8-.     50  pp.     S\)\. 

8.  Wimlmills  1or  Irrigation,  by  Edward  Charles  Murphy.     1897.     8^^.     49  pp.     8  pi. 

9.  Irrig.ition  near  Greeley,  Colorado,  by  David  lioyd.     1897.     8^.     90  pp.     21  pi. 

10.  Irrig.ition  in  Mcsilla  V.iUev,  New  Mexiio.  by  F.  C.  Barker.     1898.     8-.     51  ]ip.     11  pi. 

11.  River  Heights  for  1896,  by' Arthur  T.  Davis.'    1897.     8-.     100  pp. 

12.  Water  Resources  of  Southeastern  Nebraska,  by  Nelson  H.  Darton.     1898.     8-.     55  pp.     21  pi. 

13.  Irrigation  Systems  in  Texas,  by  William  Ferguson  Huts(m.     1898.     8\     67  pp.     10  id. 

14.  New  Tests  of  Certain  Tumps  and  Water-Lifts  used  in  Irrigation,  by  Ozni  T.  Hood.     1889.     8-^. 
91  pp.     1  pi. 

15.  Operations  at  River  Stations.  1897,  Part  I.     1898.     8.     100  pp. 

16.  Operations  at  River  Stations.  1897.  Part  II.     1898.     8-.     101-200  pp. 

17.  Irrigation  near  Bakerslield,  California,  by  C.  E.  Grunsky.     1898.     8^.     96  pp.     16  pi. 

18.  Irrigation  near  Fresno,  California,  by  C.E.  (Jrunsky.     1898.     8-.     94  pp.     14  pi. 

19.  Irrigation  near  Merced,  California,  by  C.  E.  Grunskv.     1899.     8*^.     59  pp.     U  pi. 

20.  Experiments  with  Windmills,  by  T.  O.  Perry.     1899.     8^.     97  pp.     12  pi. 

21.  Wells  of  Northern  Indiana,  by  Frank  Leverett.      1899.     8^.     82  pp.     2  pi. 

22.  Sewage  Irrigation,  Tart  II,  bv  George  W.  Rafter.     1899.     8'^.     100  pji.     7  jd. 

23.  Water-Right  Problems  of  Bighorn  iilountains.  by  Elwood  Mead.     1899.     8-.     62  pp.     7  pi. 


,    96  pp. 

.     7  pi. 

39  pp. 

12  pk 

65  pp. 

12i>l. 

VIII 


ADVERTISEMEKT. 


Ill  presK: 

24.  Water   Resources   of  the    State   of   New   ^'ork,    Part   I,    by   George   W.    Rafter.     1899.    8°. 
99  pp.     13  pi. 

25.  Water  Resources   of  the  State  of  New   York,   Part  II,   by  Cieorge  W.   Rafter.     1899.     8°. 
101-200  pp.     12  pi. 

26.  Wells  of  Soutliern  Indiana  (Contiiiuatiiiu  uf  Nil.  21),  by  Frank  Leverett.     1899.     8-.     64  pp. 

Ill  preparation: 

27.  Oi)eratious  at  River  Stations,  1898,  Part  I. 

28.  Operations  at  River  Statious,  1898,  Part  II. 

29.  Wells  an<l  Windmills  in  Nebraska,  by  Edwin  H.  Barbunr. 

30.  Water  Resources  of  the  Lower  Peninsula  of  Miehigau,  by  Alfred  E.  Lane. 


TOPOGRAPHIC  MAP  OF  THE  UNITED  STATES. 

AVheu,  in  1882,  the  Geological  Survey  was  directed  by  law  to  make  a  geologic  map  of  the  United 
States  there  was  in  existence  no  suitable  topographic  map  to  serve  as  .a  base  for  the  geologic  map. 
The  jireparatiou  of  such  a  topographic  map  wiis  thci'<'forc  immediately  begun.  Abouc  one-lifth  of  the 
area  of  the  country,  excluding  Alaska,  has  now  been  thus  mapped.  The  map  is  published  in  atlas 
sheets,  each  sheet"  representing  a  small  quadrangular  district,  as  explained  under  the  next  head- 
ing. The  separate  sheets  are  sold  at  5  cents  each  wln-u  fewer  than  100  copies  are  purchased,  but  when 
thev  are  ordered  in  lots  of  100  or  more  copies,  whether  of  the  same  sheet  or  of  different  sheets,  the 
price  is  2  cents  each.  The  mapped  areas  are  widely  scattered,  nearly  every  State  being  represented. 
About  900  sheets  have  been  engraved  and  printed;  they  are  tabulated  by  States  in  the  Survey's 
■'  List  of  Publications,'  a  pamphlet  which  may  be  had  on  application. 

The  map  sheets  represent  a  great  variety  of  topographic  features,  and  with  the  aid  of  descriptive 
text  they  can  be  used  to  illustrate  ti>pographic  forms.  This  has  led  to  the  projection  of  an  educational 
series  of  topographic  folios,  for  use  wherever  geography  is  taught  in  high  schools,  academies,  and 
colleges      Of  this  series  the  first  folio  has  been  issued,  viz : 

1.  Physiograpliic  types,  by  Henry  (iaunett,  1X9S,  folio,  consisting  of  the  following  sheets  and  4 
pages  of  descriptiNo  text:  Fargo  (N.  Dak.-Mmn.),  a  region  in  youth  ;  Charleston  ( W.Va.),  a  region  in 
maturity  ;  Caldwell  (Kans. ),  aregiou  in  old  age;  Palmyra  (Va. ),  a  rejuveualcd  region  ;  Mount  Shasta, 
(Cal.),  a  young  volcanic  mountain;  Eagle  (Wis.),  moraines;  Sun  Prairie  (Wis. ),  drumlins;  Donald- 
sonville  (La. ), river  Hood  plains;  Boothbay  (Me.),  a  tiord  coast;  Atlantic  City  (N.  J.),  a  barrier-beach 
coast. 

GEOLOGIC  ATLAS  OF  THE  UNITED  STATES. 

The  Geologic  Atlas  of  the  United  States  is  the  tiual  form  of  publication  of  the  topographic  and 
geologic  maps.  The  atlas  is  issued  in  parts,  progressively  as  the  surveys  are  extended,  and  is  designed 
ultimately  to  cover  the  entire  country. 

Under  the  plan  adopted  the  entire  area  of  the  country  is  divideil  into  small  rectangular  districts 
(designated  iiiiadranifUs),  bounded  by  certain  meridians  aud  parallels.  The  unit  of  survey  is  also  the 
unit  of  publication,  and  the  maps  aud  descriptions  of  each  rectangular  district  are  issued  as  a  folio  of 
the  Geologic  Atlas. 

Kach  folio  contains  topographic,  geologic,  economic,  and  structural  maps,  together  with  textual 
descriptions  ami  explanations,  and  is  designated  by  the  name  of  a  princijial  town  or  of  a  prominent 
natural  feature  within  the  district. 

Two  forms  of  issue  have  been  adopted,  a  "library  edition''  and  a  "Held  edition."  In  both  the 
sheets  are  bound  between  heavy  paper  covers,  but  the  library  copies  are  permanently  bound,  while 
the  sheets  and  covers  of  the  field  copies  are  only  temporarily  wired  together. 

Under  the  law  a  copy  of  each  folio  is  sent  to  certain  public  libraries  .and  educational  institu- 
tions. The  remainder  are  sold  at  2.")  cents  each,  except  such  as  contain  an  unusual  amount  of  matter, 
whicli  are  priced  accordingly.  Prepayment  is  obligatory.  The  folios  ready  for  distribution  are  listed 
below. 


No. 

Xamo  of  sheet. 

State. 

Limiting  meridians. 

Limiting  parallels. 

Area,  in 
aqnaro 
miles. 

Price, 

iu 
cents. 

1 

Livingston 

Montana'- 

110°-111° 
1                          85°-85o  30' 

120°  30'-121= 
84°  3U'-85° 

121f-121°  ;10' 
850-85°  30' 

105°-105°  30' 

85°  :iO'-86° 

106°  45'-107°  15' 

I                            77°  30'-7S° 

120=  30'-1-Jlo 

82°  30'-8;i° 

45°-46° 

34°  30'-35° 

38°  30'-39o 
35°  30'-36o 
38°  30'-39° 
35°-35°  30' 
38°  30'-39° 
35°-35°  30' 
38°  45'-39° 

30°-39o  30' 

38=-38°  30' 

;i6°  :iO'-37° 

3,354 

980 

932 
969 
932 
976 
932 
975 
465 

925 

938 

957 

25 
25 

3 
4 

5 
6 

Placerville 

Kingston 

Sacramento 

\  Tennessee 

Cilifornia 

Tennessee 

Californi:i 

Tenuessee 

Colcnaiio 

Tennessee 

Coluraiio 

25 
25 
25 
25 

7 

Pikes  Peak  (out  of  stock) 

25 

25 

n 

Anthracite-Cresteil  liiitte 

Harpers  Ferry 

Jackson  

EstillviUe 

50 

10 

11 

12 

MVest  Virginia.. 
[Maryland 

California 

[Virginia 

Kenlurky 

Tennessee 

25 
25 
25 

ADVERTISEMENT. 


IX 


No. 


Naiiie  I'f  slu'ot. 


Frt'derickaburg. 

Staunton 

Lnssen  l*riik.... 

Kuoxville 

MarysviUu 

Snnirtsvjllo 


Clevebind 

PikeviUe 

ilcMiunville. 


23     Noniiiii  . 


Tliree  Forks 

Louduu 


24 
25 

2G 

27 

28 


29  i  NerjuliiCitv. 


If  Yellowstone 
\     tional  I'ark, 


/Alaryliuul 

1  Vir;riiiij» 

I  \'ii-y,ini;i 

iWi'Mf  \'ir;;inia. 

C'alil'oruia 

iTeuiicflsi-e 

\North  Carolina 

Calit'oruia 

California 

{Alalmiua.- 
Georgiii . . . 
Teunt-'ssee 
Tennessee 
Tennessee 
Tomiessee 
fMarvlaml. 
\Virginia .. 
Montana. . 
Tennessee 
/Virginia 


::;) 


California  . 


AVyoming 


32 

33 
34 
35 
36 


Pocubontas |\ West  Virginia . 

Morristo wn Tennessee 

.(Virginia 

Piedmont ■/Maryland 

'    ilWest  Virginia. 

(Nevada  City. 
Grass  \'alleV. 
Banner  Hill  . 
(Oallatin  .. 
Na-  1  Canyon... 
1 Shoshone. 

[Lake _, 

Pyramid  Peak ;  California 

T^'      11-  f  Virginia 

^''■*^"^^*" \Weit  Virginia.. 

Briceville Tennessee 

Bnckliannon West  Virginia    . 

Gadsden |  Alabama 

Pueblo Colorado 

Do\mieville California 

Butte  Special 1  Montana 

Trnckee !  California 

"Wartbiirg ■  Tennessee 

Sonora I  California 

Nueces ,  Texas  

Bid-well  Bar ,  (.'alifnrnia 

rr  11  (Virginia 

T-'™"'^11 '\\Ve»tTirgima.. 

Boise I  Idaho 

Kicbiuonil ,  Kentucky 

Londim ,  Kenliu-ky 

Teumile  District  Special \  Colorado 

Roseburg i  Oi'egou 


I.iniitiliir  iniu'idians 


79^-7!P  30' 

l-21o_122o 

830  30'-84'= 

121°  :!0'-122o 
1210-1210  30' 

850  30'-86o 

84O'30'-»5o 
850-860  30' 
S50  30'-8CO 

TOO  30'--7o 

1110-1120 
840-810  30' 
810-810  30' 
830-830  30' 


(121 J  00'  25"-121o  03'  45" 
\rn°  01'  3o"-121o  05'  04" 
ll20o  57/  05"-121o  00'  '.'S" 


120O-120O  30' 

790-790  30' 

84°-840  30' 

80O-80O  30' 

860-81)0  30' 

1040  30'-105o 

1200  30'-121o 

1120  29'  30"-112o  36'  42" 

1200-120°  30' 

840  30'-85o 

120O-120O  30' 

lOOO-lOOO  30' 

1210-1210  30' 

>  810  30'-82o 

1I60-11C0  3D' 

840-840  30' 

S40-840  30' 

106O  8'-106o  16' 

1230-1230  30' 


Liniitiu^  ]>nrallol8. 


380-38O  30' 

3SO-38°  30' 

40°-41° 

35°  30'-36o 

390-390  30' 
390-390  30' 


Area,  iu 
square 
milee. 


Price, 

tu 
cents. 


390  13' 
390  10' 
390  13' 


390-390  30'  925 

50"-39'  17'  16"  11.05 

22"-39o  13'  50"  12.09 

50"-39o  17'  16"  11.05 


3,412 


938  ' 

938 

3,634 

925 

925 
925 


25 
25 
25 


350-350  30' 
350  30'-36o 
350  30'-36o 

975 
909 
969 

25 
25 
2."> 

380-380  30' 

938 

25 

450-460 
350  30'-36o 

3,354 
969 

50 
25 

370-370  30' 

951 

25 

30O-30O  30' 

963 

25 

932  25 

38°  30'-39°  932  25 

36°-36°  30'  963  '   25 

38°  30'-39o  932  25 

340-340  30'  986  '    25 

380-380  30'  938  50 

390  30'-4UO  919  25 

450  59'  28"-46o  02'  54"  22.80  ;    50 

390-390  30'  925  25 

36°-363  30'  963  23 

37°  30'-38°  944  ,    25 

29°  30'-30o  1,035  \         25 

390  30'-40o  918  25 

370-370  30'  950  25 

430  30'-44o  804  1    25 

370  30'-38°  944  '    25 

37°-37°  30'  95D  25 

390  22'  30"-39°  30'  30"  55  25 

430-430  30'  871  ,    25 


STATISTICAL  PAPEK.S. 

Mineral  Resources  of  tlie  United  .States  [18X2].  hy  Albert  AVilliauis,  jr.  1883.  8-'.  xvii,  813  pp. 
Price  50  cents. 

Mineral  Resources  of  the  Tniteil  State.s.  1883  ;iu(l  1SX4,  liv  Albert  Williams,  jr.  1885.  8^.  xiv, 
1016  pp.     Price  60  cents. 

Mineral  Resources  of  the  United  States,  1885.  Division  of  Mining  Statistics  and  Technologv. 
1886.     8".     vii,  576  p]).     Price  40  cents. 

Mineral  Resources  of  the  United  States,  1886,  by  David  T.  Day.  1887.  8^.  viii,  813  pp.  Price 
(50  cents. 

Mineral  Resources  of  the  United  States,  1887,  by  David  T.  Day.  1888.  8-.  vii,  832  i)p.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  1888,  by  David  T.  Day.  1890.  ,8.  vii,  652  pp.  Price 
■  50  cents. 

Mineral  Resources  of  the  United  States,  1889  and  1890,  by  David  T.  Day.  1892.  S\  viii,  671  pp. 
Price  50  cents. 

ilineral  Re,sourecs  of  the  United  States,  1891,  by  David  T.  Day.  1893.  8^.  vii,  630  pp.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  1892,  by  David  T,  Day.  1893.  8^.  vii,  850  pp.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  189.3,  by  David  T.  Day.  1894.  8-.  viii,  810  pp.  Price 
50  cents. 


I 


X  ADVERTISEMENT. 

On  March  2, 1893,  the  following  provision  was  iuclnileil  in  an  act  of  Congress: 

■•I'rovidid.  That  hereafter  the  report  of  the  mineral  resonrces  of  the  United  States  shall  he 
issued  as  a  part  of  the  report  of  the  Ilireetor  of  the  Geological  yurvej'." 

In  compliance  with  this  legislation  the  following  reports  have  been  published: 

Mineral  Kesonrees  of  the  Tnitcd  .States,  1894,  David  T.  Day,  Chief  of  Division.  1895.  8^-.  xv, 
fU6  pp.,  23  pi. ;  xis,  I'.io  pp.,  (i  pi.     Being  Parts  III  and  IV  of  the  Sixteenth  Annual  Report. 

Mineral  Kesourees  of  the  United  States,  189.5,  David  T.  Day,  Chief  of  Division.  1896.  8°. 
xxiii,  i542  pp.,  8  pi.  and  maps;  iii,  .543-1058  pp.,  9-13  pi.  Being  Part  III  (in  2  vols.)  of  the  Seventeenth 
Annual  Report. 

Mineral  Resources  of  the  I'uited  States,  1896,  David  T,  Day,  Chief  of  Division.  1897.  8". 
xii,  642  pp..  1  pi. ;  643-1400  pp.     Being  Part  V  (in  2  vols. )  of  the  Nineteenth  Annual  Report. 

Jlineral  Resources  of  the  United  States,  1897,  David  T.  Day,  Chief  of  Division.  1898.  8°. 
viii,  651  pp.,  11  pi. ;  viii,  706  pp.     Being  Part  VI  (in  2  vols.)  of  the  Nineteenth  Annual  Report. 

The  money  received  from  the  sale  .of  the  Survey  iiul)lieations  is  dejjosited  in  the  Treasury,  and 
the  Secret  ary  of  that  Department  declines  to  receive  Ijauk  i-liecks.  (b-afts,  or  jiostage  stamps ;  all  remit- 
tances, therefore,  must  lie  by  M<)^"^;v  order,  made  payable  to  the  Director  of  the  United  States 
(ieiilogieal  Survey,  or  in  currexcv — thi'  exact  amount.  Correspondence  relating  to  the  publiciitions 
of  the  .Suvvi'y  should  be  ad<lvesst'd  to 

The  Direct< >r, 

U.NlTEi)  States  Geological  Si'KVEY, 
Wasiiinuton,  D.  C,  Jpi-il,  lt<99.  Washington,  D.  C. 


[Tiiko  lIiiH  loaf  out  and  paHlo  tlm  si'|iarati-(l  tilU's  iijioii  tliroe  of  your  cjita- 
loK"*'  t-ards.  TIio  lirMl.  and  sfcoud  tilloa  m-cd  no  adilition  :  over  the  third  write 
thut  subject  iinilor  wliicli  you  would  jdaco  the  t)0olt  in  your  library.] 


LIBRARY  CATALOGITE  SLIPS. 

TJuited  States.     Department  of  the  interior.     {U.  S.  tieoloijical  Kurveij.) 

I)i!])art.mcnt  of  tho  interior  |  —  |  Moiiosiaplis  |  of  ttio  |  United 
Status  s'-ologioal  .survey  |  Volume  XXXII  |  Part  II  |  [Seal  of 
tho  (lepartnient]  |  Wasliiiigtoii  |  government  itrinting  ofiicci  |  1X99 

Second  title:  United  States  gcologieal  survey  |  Charles  D. 
Waleott,  director  |  —  |  Geology  |  of  the  |  Yellowstone  national 
park  I  —  I  Part  II  |  Descriptive  geology,  jietrography,  and  pale- 
ontology I  by  I  Arnold  Hague,  J.  P.  Id(ling.s,  W.  H.  Weed  |  and  | 
C.  D.  Waleott,  (!.  II.  Girty,  T.  W.  Stanton,  and  F.  II.  Knowltou  | 
[Vignette]  | 

Washington  |  government  printing  office  |  1899 

4°.    xvii,893pp.    121  pi. 


Hague  (Arnold)  aiHl  others. 

United    States   geological    survey    |    Charles   D.  Waleott,   di- 
rector I  —  I  Geology  |  of  the   |  Yellowstone   national  park  |  —  | 
Part  II  I  Descriptive  geology,  petrography,  and  p.aleontology  | 
C  by  I  Arnold  Hague,  ,J.  P.  Idiiings,  W.  H.  Weed   |  ami  |  C.  D.  Wal- 

g  cott,  G.  H.  Girty,   T.  W.  Stanton,  and  F.  H.  Knowlton   |    [Vig- 

^  uette]  I 

Washington  |  government  printing  oflice  |  1899 
4".    xvii,  893  pp.    121  pi. 

[TTnitko  Rtate.s.    Departmi'nt  o/   Ikr  interior.     {U.   S.   f/enlogicai  survey.) 
Monograpb  XXXII.] 


United   States   geological    .survey   |    Charles    D.   Waleott,   di- 
rector  I  —  I  Geology  |  of  the  |   Yellowstone  national  park   |  —  | 
Part  II  I  Descriptive  geology,  petrography,  and  paleontology  | 
by  I  Arnold   Hague,  .1.  P.  Iddings,  W.  H.  Weed   |   and   [  CD.  Wal- 
eott, G.  11.  Girty,   T.  W.   Stanton,   and  F.  H.  Knowlton    |    [Vig- 
nette] I 

Washington  |  governincnt  printing  oDice  |  lSfl9 

4°.    xvii,  893  pp.     121  pi. 

[Uniti-iI)  States.    lii-jiarlmnit   of    tin'  intniur.      {II.   S.  genioijical  eurvry. 
Monograpb  XXXH.] 


MON  XXXII .58 


